diff --git a/doc/sphinx/Clusters_from_Scratch/active-active.rst b/doc/sphinx/Clusters_from_Scratch/active-active.rst
index 391f9b30cd..ac8a26a13c 100644
--- a/doc/sphinx/Clusters_from_Scratch/active-active.rst
+++ b/doc/sphinx/Clusters_from_Scratch/active-active.rst
@@ -1,346 +1,346 @@
.. index::
single: storage; active/active
Convert Storage to Active/Active
--------------------------------
The primary requirement for an Active/Active cluster is that the data
required for your services is available, simultaneously, on both
machines. Pacemaker makes no requirement on how this is achieved; you
could use a Storage Area Network (SAN) if you had one available, but
since DRBD supports multiple Primaries, we can continue to use it here.
.. index::
single: GFS2
single: DLM
single: filesystem; GFS2
Install Cluster Filesystem Software
###################################
The only hitch is that we need to use a cluster-aware filesystem. The
one we used earlier with DRBD, xfs, is not one of those. Both OCFS2
and GFS2 are supported; here, we will use GFS2.
On both nodes, install the GFS2 command-line utilities required by
cluster filesystems:
.. code-block:: none
# yum install -y gfs2-utils
Additionally, install Distributed Lock Manager (DLM) on both nodes.
To do so, download the RPM from the `CentOS composes artifacts tree `_,
onto your nodes and then run the following
command:
.. code-block:: none
# rpm -i dlm-4.1.0-1.el8.x86_64.rpm
Configure the Cluster for the DLM
#################################
The DLM control daemon needs to run on both nodes, so we'll start by creating a
resource for it (using the **ocf:pacemaker:controld** resource script), and clone
it:
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib dlm_cfg
[root@pcmk-1 ~]# pcs -f dlm_cfg resource create dlm \
ocf:pacemaker:controld op monitor interval=60s
[root@pcmk-1 ~]# pcs -f dlm_cfg resource clone dlm clone-max=2 clone-node-max=1
[root@pcmk-1 ~]# pcs resource status
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
* WebSite (ocf::heartbeat:apache): Started pcmk-2
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-2 ]
* Slaves: [ pcmk-1 ]
* WebFS (ocf::heartbeat:Filesystem): Started pcmk-2
[root@pcmk-1 ~]# pcs resource config
Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2)
Attributes: cidr_netmask=24 ip=192.168.122.120
Operations: monitor interval=30s (ClusterIP-monitor-interval-30s)
start interval=0s timeout=20s (ClusterIP-start-interval-0s)
stop interval=0s timeout=20s (ClusterIP-stop-interval-0s)
Resource: WebSite (class=ocf provider=heartbeat type=apache)
Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status
Operations: monitor interval=1min (WebSite-monitor-interval-1min)
start interval=0s timeout=40s (WebSite-start-interval-0s)
stop interval=0s timeout=60s (WebSite-stop-interval-0s)
Clone: WebData-clone
Meta Attrs: clone-max=2 clone-node-max=1 notify=true promotable=true promoted-max=1 promoted-node-max=1
Resource: WebData (class=ocf provider=linbit type=drbd)
Attributes: drbd_resource=wwwdata
Operations: demote interval=0s timeout=90 (WebData-demote-interval-0s)
monitor interval=60s (WebData-monitor-interval-60s)
notify interval=0s timeout=90 (WebData-notify-interval-0s)
promote interval=0s timeout=90 (WebData-promote-interval-0s)
reload interval=0s timeout=30 (WebData-reload-interval-0s)
start interval=0s timeout=240 (WebData-start-interval-0s)
stop interval=0s timeout=100 (WebData-stop-interval-0s)
Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
Attributes: device=/dev/drbd1 directory=/var/www/html fstype=xfs
Operations: monitor interval=20s timeout=40s (WebFS-monitor-interval-20s)
start interval=0s timeout=60s (WebFS-start-interval-0s)
stop interval=0s timeout=60s (WebFS-stop-interval-0s)
Activate our new configuration, and see how the cluster responds:
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib-push dlm_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.1.0-3.el8-7c3f660707) - partition with quorum
* Last updated: Wed Jul 13 10:57:20 2021
* Last change: Wed Jul 13 10:57:15 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 7 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
* WebFS (ocf::heartbeat:Filesystem): Started pcmk-1
* Clone Set: dlm-clone [dlm]:
* Started: [ pcmk-1 pcmk-2 ]
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Create and Populate GFS2 Filesystem
###################################
Before we do anything to the existing partition, we need to make sure it
is unmounted. We do this by telling the cluster to stop the WebFS resource.
This will ensure that other resources (in our case, Apache) using WebFS
are not only stopped, but stopped in the correct order.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource disable WebFS
[root@pcmk-1 ~]# pcs resource
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Stopped
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
* WebFS (ocf::heartbeat:Filesystem): Stopped (disabled)
* Clone Set: dlm-clone [dlm]:
* Started: [ pcmk-1 pcmk-2 ]
You can see that both Apache and WebFS have been stopped, and that **pcmk-1**
is currently running the promoted instance for the DRBD device.
Now we can create a new GFS2 filesystem on the DRBD device.
.. WARNING::
This will erase all previous content stored on the DRBD device. Ensure
you have a copy of any important data.
.. IMPORTANT::
Run the next command on whichever node has the DRBD Primary role.
Otherwise, you will receive the message:
.. code-block:: none
/dev/drbd1: Read-only file system
.. code-block:: none
[root@pcmk-2 ~]# mkfs.gfs2 -p lock_dlm -j 2 -t mycluster:web /dev/drbd1
It appears to contain an existing filesystem (xfs)
This will destroy any data on /dev/drbd1
Are you sure you want to proceed? [y/n] y
Discarding device contents (may take a while on large devices): Done
Adding journals: Done
Building resource groups: Done
Creating quota file: Done
Writing superblock and syncing: Done
Device: /dev/drbd1
Block size: 4096
Device size: 0.50 GB (131059 blocks)
Filesystem size: 0.50 GB (131055 blocks)
Journals: 2
Journal size: 8MB
Resource groups: 4
Locking protocol: "lock_dlm"
Lock table: "mycluster:web"
UUID: 19712677-7206-4660-a079-5d17341dd720
The ``mkfs.gfs2`` command required a number of additional parameters:
-* ``-p lock_dlm`` specifies that we want to use the kernel's DLM.
+* ``-p lock_dlm`` specifies that we want to use DLM-based locking.
* ``-j 2`` indicates that the filesystem should reserve enough
space for two journals (one for each node that will access the filesystem).
* ``-t mycluster:web`` specifies the lock table name. The format for this
field is ``:``. For ``CLUSTERNAME``, we need to use the
same value we specified originally with ``pcs cluster setup --name`` (which is
also the value of **cluster_name** in ``/etc/corosync/corosync.conf``). If
you are unsure what your cluster name is, you can look in
``/etc/corosync/corosync.conf`` or execute the command
- ``pcs cluster corosync pcmk-1 | grep cluster_name``.
+ ``pcs cluster corosync | grep cluster_name``.
Now we can (re-)populate the new filesystem with data
(web pages). We'll create yet another variation on our home page.
.. code-block:: none
[root@pcmk-1 ~]# mount /dev/drbd1 /mnt
[root@pcmk-1 ~]# cat <<-END >/mnt/index.html
My Test Site - GFS2
END
[root@pcmk-1 ~]# chcon -R --reference=/var/www/html /mnt
[root@pcmk-1 ~]# umount /dev/drbd1
[root@pcmk-1 ~]# drbdadm verify wwwdata
Reconfigure the Cluster for GFS2
################################
With the WebFS resource stopped, let's update the configuration.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource config WebFS
Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
Attributes: device=/dev/drbd1 directory=/var/www/html fstype=xfs
Meta Attrs: target-role=Stopped
Operations: monitor interval=20s timeout=40s (WebFS-monitor-interval-20s)
start interval=0s timeout=60s (WebFS-start-interval-0s)
stop interval=0s timeout=60s (WebFS-stop-interval-0s)
The fstype option needs to be updated to **gfs2** instead of **xfs**.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource update WebFS fstype=gfs2
[root@pcmk-1 ~]# pcs resource config WebFS
Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
Attributes: device=/dev/drbd1 directory=/var/www/html fstype=gfs2
Meta Attrs: target-role=Stopped
Operations: monitor interval=20s timeout=40s (WebFS-monitor-interval-20s)
start interval=0s timeout=60s (WebFS-start-interval-0s)
stop interval=0s timeout=60s (WebFS-stop-interval-0s)
GFS2 requires that DLM be running, so we also need to set up new colocation
and ordering constraints for it:
.. code-block:: none
[root@pcmk-1 ~]# pcs constraint colocation add WebFS with dlm-clone INFINITY
[root@pcmk-1 ~]# pcs constraint order dlm-clone then WebFS
Adding dlm-clone WebFS (kind: Mandatory) (Options: first-action=start then-action=start)
We also need to update the **no-quorum-policy** property to **freeze**. By
default, the value of **no-quorum-policy** is set to **stop**, indicating that
once quorum is lost, all the resources on the remaining partition will
immediately be stopped. Typically this default is the safest and most optimal
option, but unlike most resources, GFS2 requires quorum to function. When
quorum is lost both the applications using the GFS2 mounts and the GFS2 mount
itself cannot be correctly stopped. Any attempts to stop these resources
without quorum will fail, which will ultimately result in the entire cluster
being fenced every time quorum is lost.
To address this situation, set **no-quorum-policy** to **freeze** when GFS2 is
in use. This means that when quorum is lost, the remaining partition will do
nothing until quorum is regained.
.. code-block:: none
[root@pcmk-1 ~]# pcs property set no-quorum-policy=freeze
.. index::
pair: filesystem; clone
Clone the Filesystem Resource
#############################
Now that we have a cluster filesystem ready to go, we can configure the cluster
so both nodes mount the filesystem.
Clone the filesystem resource in a new configuration.
Notice how pcs automatically updates the relevant constraints again.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib active_cfg
[root@pcmk-1 ~]# pcs -f active_cfg resource clone WebFS
[root@pcmk-1 ~]# pcs -f active_cfg constraint
[root@pcmk-1 ~]# pcs -f active_cfg constraint
Location Constraints:
Resource: WebSite
Enabled on:
Node: pcmk-1 (score:50)
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
promote WebData-clone then start WebFS-clone (kind:Mandatory)
start WebFS-clone then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
WebFS-clone with WebData-clone (score:INFINITY) (with-rsc-role:Master)
WebSite with WebFS-clone (score:INFINITY)
Ticket Constraints:
Tell the cluster that it is now allowed to promote both instances to be DRBD
Primary.
.. code-block:: none
[root@pcmk-1 ~]# pcs -f active_cfg resource update WebData-clone promoted-max=2
Finally, load our configuration to the cluster, and re-enable the WebFS resource
(which we disabled earlier).
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib-push active_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs resource enable WebFS
After all the processes are started, the status should look similar to this.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource
[root@pcmk-1 ~]# pcs resource
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 pcmk-2 ]
* Clone Set: dlm-clone [dlm]:
* Started: [ pcmk-1 pcmk-2 ]
* Clone Set: WebFS-clone [WebFS]:
* Started: [ pcmk-1 pcmk-2 ]
Test Failover
#############
Testing failover is left as an exercise for the reader.
With this configuration, the data is now active/active. The website
administrator could change HTML files on either node, and the live website will
show the changes even if it is running on the opposite node.
If the web server is configured to listen on all IP addresses, it is possible
to remove the constraints between the WebSite and ClusterIP resources, and
clone the WebSite resource. The web server would always be ready to serve web
pages, and only the IP address would need to be moved in a failover.
diff --git a/doc/sphinx/Clusters_from_Scratch/active-passive.rst b/doc/sphinx/Clusters_from_Scratch/active-passive.rst
index 72a6e9e12c..ee4a9b2ad3 100644
--- a/doc/sphinx/Clusters_from_Scratch/active-passive.rst
+++ b/doc/sphinx/Clusters_from_Scratch/active-passive.rst
@@ -1,285 +1,315 @@
Create an Active/Passive Cluster
--------------------------------
.. index::
pair: resource; IP address
Add a Resource
##############
-Our first resource will be a unique IP address that the cluster can bring up on
-either node. Regardless of where any cluster service(s) are running, end
-users need a consistent address to contact them on. Here, I will choose
-192.168.122.120 as the floating address, give it the imaginative name ClusterIP
-and tell the cluster to check whether it is running every 30 seconds.
+Our first resource will be a floating IP address that the cluster can bring up
+on either node. Regardless of where any cluster service(s) are running, end
+users need to be able to communicate with them at a consistent address. Here,
+we will use **192.168.122.120** as the floating IP address, give it the
+imaginative name **ClusterIP**, and tell the cluster to check whether it is
+still running every 30 seconds.
.. WARNING::
- The chosen address must not already be in use on the network.
- Do not reuse an IP address one of the nodes already has configured.
+ The chosen address must not already be in use on the network, on a cluster
+ node or elsewhere. Do not reuse an IP address one of the nodes already has
+ configured.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource create ClusterIP ocf:heartbeat:IPaddr2 \
ip=192.168.122.120 cidr_netmask=24 op monitor interval=30s
Another important piece of information here is **ocf:heartbeat:IPaddr2**.
This tells Pacemaker three things about the resource you want to add:
* The first field (**ocf** in this case) is the standard to which the resource
- script conforms and where to find it.
+ agent conforms and where to find it.
-* The second field (**heartbeat** in this case) is standard-specific; for OCF
- resources, it tells the cluster which OCF namespace the resource script is in.
+* The second field (**heartbeat** in this case) is known as the provider.
+ Currently, this field is supported only for OCF resources. It tells Pacemaker
+ which OCF namespace the resource script is in.
-* The third field (**IPaddr2** in this case) is the name of the resource script.
+* The third field (**IPaddr2** in this case) is the name of the resource agent,
+ the executable file responsible for starting, stopping, monitoring, and
+ possibly promoting and demoting the resource.
To obtain a list of the available resource standards (the **ocf** part of
**ocf:heartbeat:IPaddr2**), run:
.. code-block:: none
[root@pcmk-1 ~]# pcs resource standards
lsb
ocf
service
systemd
To obtain a list of the available OCF resource providers (the **heartbeat**
part of **ocf:heartbeat:IPaddr2**), run:
.. code-block:: none
[root@pcmk-1 ~]# pcs resource providers
heartbeat
openstack
pacemaker
Finally, if you want to see all the resource agents available for
a specific OCF provider (the **IPaddr2** part of **ocf:heartbeat:IPaddr2**), run:
.. code-block:: none
[root@pcmk-1 ~]# pcs resource agents ocf:heartbeat
apache
aws-vpc-move-ip
aws-vpc-route53
awseip
awsvip
azure-events
.
. (skipping lots of resources to save space)
.
symlink
tomcat
vdo-vol
VirtualDomain
Xinetd
Now, verify that the IP resource has been added, and display the cluster's
status to see that it is now active:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:22:10 2021
* Last change: Tue Jan 26 19:20:28 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 1 resource instance configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Perform a Failover
##################
Since our ultimate goal is high availability, we should test failover of
our new resource before moving on.
First, find the node on which the IP address is running.
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:22:10 2021
* Last change: Tue Jan 26 19:20:28 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 1 resource instance configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
You can see that the status of the **ClusterIP** resource
is **Started** on a particular node (in this example, **pcmk-1**).
Shut down Pacemaker and Corosync on that machine to trigger a failover.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster stop pcmk-1
pcmk-1: Stopping Cluster (pacemaker)...
pcmk-1: Stopping Cluster (corosync)...
.. NOTE::
- A cluster command such as ``pcs cluster stop `` can be run from any
- node in the cluster, not just the affected node.
+ A cluster command such as ``pcs cluster stop `` can be run from
+ any node in the cluster, not just the node where the cluster services will
+ be stopped. Running ``pcs cluster stop`` without a ```` stops the
+ cluster services on the local host. The same is true for ``pcs cluster
+ start`` and many other such commands.
Verify that pacemaker and corosync are no longer running:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Error: error running crm_mon, is pacemaker running?
Could not connect to the CIB: Transport endpoint is not connected
crm_mon: Error: cluster is not available on this node
Go to the other node, and check the cluster status.
.. code-block:: none
- [root@pcmk-1 ~]# pcs status
+ [root@pcmk-2 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:25:26 2021
* Last change: Tue Jan 26 19:20:28 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 1 resource instance configured
Node List:
* Online: [ pcmk-2 ]
* OFFLINE: [ pcmk-1 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Notice that **pcmk-1** is **OFFLINE** for cluster purposes (its **pcsd** is still
active, allowing it to receive ``pcs`` commands, but it is not participating in
the cluster).
Also notice that **ClusterIP** is now running on **pcmk-2** -- failover happened
automatically, and no errors are reported.
.. topic:: Quorum
If a cluster splits into two (or more) groups of nodes that can no longer
- communicate with each other (aka. *partitions*), *quorum* is used to prevent
- resources from starting on more nodes than desired, which would risk
- data corruption.
+ communicate with each other (a.k.a. *partitions*), *quorum* is used to
+ prevent resources from starting on more nodes than desired, which would
+ risk data corruption.
A cluster has quorum when more than half of all known nodes are online in
the same partition, or for the mathematically inclined, whenever the following
- equation is true:
+ inequality is true:
.. code-block:: none
total_nodes < 2 * active_nodes
For example, if a 5-node cluster split into 3- and 2-node paritions,
the 3-node partition would have quorum and could continue serving resources.
If a 6-node cluster split into two 3-node partitions, neither partition
would have quorum; pacemaker's default behavior in such cases is to
stop all resources, in order to prevent data corruption.
Two-node clusters are a special case. By the above definition,
a two-node cluster would only have quorum when both nodes are
- running. This would make the creation of a two-node cluster pointless,
- but corosync has the ability to treat two-node clusters as if only one node
- is required for quorum.
+ running. This would make the creation of a two-node cluster pointless.
+ However, corosync has the ability to require only one node for quorum in a
+ two-node cluster.
The ``pcs cluster setup`` command will automatically configure **two_node: 1**
in ``corosync.conf``, so a two-node cluster will "just work".
- If you are using a different cluster shell, you will have to configure
+ .. NOTE::
+
+ You might wonder, "What if the nodes in a two-node cluster can't
+ communicate with each other? Wouldn't this **two_node: 1** setting
+ create a split-brain scenario, in which each node has quorum separately
+ and they both try to manage the same cluster resources?"
+
+ As long as fencing is configured, there is no danger of this. If the
+ nodes lose contact with each other, each node will try to fence the
+ other node. Resource management is disabled until fencing succeeds;
+ neither node is allowed to start, stop, promote, or demote resources.
+
+ After fencing succeeds, the surviving node can safely recover any
+ resources that were running on the fenced node.
+
+ If the fenced node boots up and rejoins the cluster, it does not have
+ quorum until it can communicate with the surviving node at least once.
+ This prevents "fence loops," in which a node gets fenced, reboots,
+ rejoins the cluster, and fences the other node. This protective
+ behavior is controlled by the **wait_for_all: 1** option, which is
+ enabled automatically when **two_node: 1** is configured.
+
+ If you are using a different cluster shell, you may have to configure
``corosync.conf`` appropriately yourself.
Now, simulate node recovery by restarting the cluster stack on **pcmk-1**, and
check the cluster's status. (It may take a little while before the cluster
gets going on the node, but it eventually will look like the below.)
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster start pcmk-1
pcmk-1: Starting Cluster...
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:28:30 2021
* Last change: Tue Jan 26 19:28:27 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 1 resource instance configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
.. index:: stickiness
Prevent Resources from Moving after Recovery
############################################
In most circumstances, it is highly desirable to prevent healthy
resources from being moved around the cluster. Moving resources almost
always requires a period of downtime. For complex services such as
databases, this period can be quite long.
To address this, Pacemaker has the concept of resource *stickiness*,
which controls how strongly a service prefers to stay running where it
is. You may like to think of it as the "cost" of any downtime. By
default, [#]_ Pacemaker assumes there is zero cost associated with moving
resources and will do so to achieve "optimal" [#]_ resource placement.
We can specify a different stickiness for every resource, but it is
often sufficient to change the default.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource defaults update resource-stickiness=100
Warning: Defaults do not apply to resources which override them with their own defined values
[root@pcmk-1 ~]# pcs resource defaults
Meta Attrs: rsc_defaults-meta_attributes
resource-stickiness=100
.. [#] Pacemaker may be built such that a positive resource-stickiness is
automatically added to resource defaults. You can check your
configuration to see if this is present.
-.. [#] Pacemaker's definition of optimal may not always agree with that of a
- human's. The order in which Pacemaker processes lists of resources and
+.. [#] Pacemaker's default definition of "optimal" may not always agree with
+ yours. The order in which Pacemaker processes lists of resources and
nodes creates implicit preferences in situations where the administrator
has not explicitly specified them.
diff --git a/doc/sphinx/Clusters_from_Scratch/ap-configuration.rst b/doc/sphinx/Clusters_from_Scratch/ap-configuration.rst
index ea1e042522..a2d72f36a1 100644
--- a/doc/sphinx/Clusters_from_Scratch/ap-configuration.rst
+++ b/doc/sphinx/Clusters_from_Scratch/ap-configuration.rst
@@ -1,366 +1,368 @@
Configuration Recap
-------------------
Final Cluster Configuration
###########################
.. code-block:: none
[root@pcmk-1 ~]# pcs resource
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 pcmk-2 ]
* Clone Set: dlm-clone [dlm]:
* Started: [ pcmk-1 pcmk-2 ]
* Clone Set: WebFS-clone [WebFS]:
* Started: [ pcmk-1 pcmk-2 ]
.. code-block:: none
[root@pcmk-1 ~]# pcs resource op defaults
Meta Attrs: op_defaults-meta_attributes
timeout=240s
.. code-block:: none
[root@pcmk-1 ~]# pcs stonith
* ipmi-fencing (stonith:fence_ipmilan): Started pcmk-1
.. code-block:: none
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
promote WebDataClone then start WebFS-clone (kind:Mandatory)
start WebFS-clone then start WebSite (kind:Mandatory)
start dlm-clone then start WebFS-clone (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
WebFS-clone with WebDataClone (score:INFINITY) (with-rsc-role:Master)
WebSite with WebFS-clone (score:INFINITY)
WebFS-clone with dlm-clone (score:INFINITY)
Ticket Constraints:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: pcmk-1 (version 1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Fri Jul 16 09:00:56 2021
Last change: Wed Jul 14 11:06:25 2021 by root via cibadmin on pcmk-1
2 nodes configured
11 resources configured
Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ipmi-fencing (stonith:fence_ipmilan): Stopped
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 pcmk-2 ]
* Clone Set: dlm-clone [dlm]:
* Started: [ pcmk-1 pcmk-2 ]
* Clone Set: WebFS-clone [WebFS]:
* Started: [ pcmk-1 pcmk-2 ]
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib --config
.. code-block:: xml
Node List
#########
.. code-block:: none
[root@pcmk-1 ~]# pcs status nodes
Pacemaker Nodes:
Online: pcmk-1 pcmk-2
Standby:
Standby with resource(s) running:
Maintenance:
Offline:
Pacemaker Remote Nodes:
Online:
Standby:
Standby with resource(s) running:
Maintenance:
Offline:
Cluster Options
###############
.. code-block:: none
[root@pcmk-1 ~]# pcs property
Cluster Properties:
cluster-infrastructure: corosync
cluster-name: mycluster
dc-version: 2.1.0-3.el8-7c3f660707
have-watchdog: false
no-quorum-policy: freeze
stonith-enabled: true
The output shows state information automatically obtained about the cluster, including:
* **cluster-infrastructure** - the cluster communications layer in use
* **cluster-name** - the cluster name chosen by the administrator when the cluster was created
* **dc-version** - the version (including upstream source-code hash) of Pacemaker
used on the Designated Controller, which is the node elected to determine what
actions are needed when events occur
The output also shows options set by the administrator that control the way the cluster operates, including:
* **stonith-enabled=true** - whether the cluster is allowed to use STONITH resources
Resources
#########
Default Options
_______________
.. code-block:: none
[root@pcmk-1 ~]# pcs resource defaults
resource-stickiness: 100
This shows cluster option defaults that apply to every resource that does not
explicitly set the option itself. Above:
-* **resource-stickiness** - Specify the aversion to moving healthy resources to other machines
+* **resource-stickiness** - Specify how strongly a resource prefers to remain
+ on its current node. Alternatively, you can view this as the level of
+ aversion to moving healthy resources to other machines.
Fencing
_______
.. code-block:: none
[root@pcmk-1 ~]# pcs stonith status
* impi-fencing (stonith:fence_ipmilan): Started pcmk-1
[root@pcmk-1 ~]# pcs stonith config
Resource: ipmi-fencing (class=stonith type=fence_ipmilan)
Attributes: ipaddr=10.0.0.1 login=testuser passwd=acd123 pcmk_host_list="pcmk-1 pcmk-2"
Operations: monitor interval=60s (ipmi-fencing-monitor-interval-60s)
Service Address
_______________
Users of the services provided by the cluster require an unchanging
address with which to access it.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource config ClusterIP
Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2)
Attributes: cidr_netmask=24 ip=192.168.122.120
Meta Attrs: resource-stickiness=0
Operations: monitor interval=30s (ClusterIP-monitor-interval-30s)
start interval=0s timeout=20s (ClusterIP-start-interval-0s)
stop interval=0s timeout=20s (ClusterIP-stop-interval-0s)
DRBD - Shared Storage
_____________________
Here, we define the DRBD service and specify which DRBD resource (from
/etc/drbd.d/\*.res) it should manage. We make it a promotable clone resource
and, in order to have an active/active setup, allow both instances to be
promoted at the same time. We also set the notify option so that the cluster
will tell DRBD agent when its peer changes state.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource show WebData-clone
Clone: WebData-clone
Meta Attrs: clone-max=2 clone-node-max=1 notify=true promotable=true promoted-max=2 promoted-node-max=1
Resource: WebData (class=ocf provider=linbit type=drbd)
Attributes: drbd_resource=wwwdata
Operations: demote interval=0s timeout=90 (WebData-demote-interval-0s)
monitor interval=60s (WebData-monitor-interval-60s)
notify interval=0s timeout=90 (WebData-notify-interval-0s)
promote interval=0s timeout=90 (WebData-promote-interval-0s)
reload interval=0s timeout=30 (WebData-reload-interval-0s)
start interval=0s timeout=240 (WebData-start-interval-0s)
stop interval=0s timeout=100 (WebData-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebData-clone
Resource: WebData-clone
colocation-WebFS-WebDataClone-INFINITY
order-WebDataClone-WebFS-mandatory
Cluster Filesystem
__________________
The cluster filesystem ensures that files are read and written correctly.
We need to specify the block device (provided by DRBD), where we want it
mounted and that we are using GFS2. Again, it is a clone because it is
intended to be active on both nodes. The additional constraints ensure
that it can only be started on nodes with active DLM and DRBD instances.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource show WebFS-clone
Clone: WebFS-clone
Resource: WebFS (class=ocf provider=heartbeat type=Filesystem)
Attributes: device=/dev/drbd1 directory=/var/www/html fstype=gfs2
Operations: monitor interval=20 timeout=40 (WebFS-monitor-interval-20)
notify interval=0s timeout=60 (WebFS-notify-interval-0s)
start interval=0s timeout=60 (WebFS-start-interval-0s)
stop interval=0s timeout=60 (WebFS-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebFS-clone
Resource: WebFS-clone
colocation-WebFS-WebDataClone-INFINITY
colocation-WebSite-WebFS-INFINITY
colocation-WebFS-dlm-clone-INFINITY
order-WebDataClone-WebFS-mandatory
order-WebFS-WebSite-mandatory
order-dlm-clone-WebFS-mandatory
Apache
______
Lastly, we have the actual service, Apache. We need only tell the cluster
where to find its main configuration file and restrict it to running on
a node that has the required filesystem mounted and the IP address active.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource show WebSite
Resource: WebSite (class=ocf provider=heartbeat type=apache)
Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status
Operations: monitor interval=1min (WebSite-monitor-interval-1min)
start interval=0s timeout=40s (WebSite-start-interval-0s)
stop interval=0s timeout=60s (WebSite-stop-interval-0s)
[root@pcmk-1 ~]# pcs constraint ref WebSite
Resource: WebSite
colocation-WebSite-ClusterIP-INFINITY
colocation-WebSite-WebFS-INFINITY
order-ClusterIP-WebSite-mandatory
order-WebFS-WebSite-mandatory
diff --git a/doc/sphinx/Clusters_from_Scratch/apache.rst b/doc/sphinx/Clusters_from_Scratch/apache.rst
index 6b955b244a..3ba5b72d1b 100644
--- a/doc/sphinx/Clusters_from_Scratch/apache.rst
+++ b/doc/sphinx/Clusters_from_Scratch/apache.rst
@@ -1,452 +1,477 @@
.. index::
single: Apache HTTP Server
Add Apache HTTP Server as a Cluster Service
-------------------------------------------
Now that we have a basic but functional active/passive two-node cluster,
we're ready to add some real services. We're going to start with
-Apache HTTP Server because it is a feature of many clusters and relatively
+Apache HTTP Server because it is a feature of many clusters and is relatively
simple to configure.
Install Apache
##############
Before continuing, we need to make sure Apache is installed on both
-hosts. We also need the wget tool in order for the cluster to be able to check
-the status of the Apache server.
+hosts. We will also allow the cluster to use the **wget** tool (this is the
+default, but **curl** is also supported) to check the status of the Apache
+server. We'll install **httpd** (Apache) and **wget** now.
.. code-block:: none
# yum install -y httpd wget
# firewall-cmd --permanent --add-service=http
# firewall-cmd --reload
.. IMPORTANT::
Do **not** enable the httpd service. Services that are intended to
be managed via the cluster software should never be managed by the OS.
It is often useful, however, to manually start the service, verify that
it works, then stop it again, before adding it to the cluster. This
allows you to resolve any non-cluster-related problems before continuing.
Since this is a simple example, we'll skip that step here.
Create Website Documents
########################
We need to create a page for Apache to serve. On |CFS_DISTRO| |CFS_DISTRO_VER|, the
-default Apache document root is /var/www/html, so we'll create an index file
-there. For the moment, we will simplify things by serving a static site
+default Apache document root is ``/var/www/html``, so we'll create an index
+file there. For the moment, we will simplify things by serving a static site
and manually synchronizing the data between the two nodes, so run this command
on both nodes:
.. code-block:: none
# cat <<-END >/var/www/html/index.html
My Test Site - $(hostname)
END
.. index::
single: Apache HTTP Server; status URL
-Enable the Apache status URL
+Enable the Apache Status URL
############################
-In order to monitor the health of your Apache instance, and recover it if
-it fails, the resource agent used by Pacemaker assumes the server-status
-URL is available. On both nodes, enable the URL with:
+Pacemaker uses the **apache** resource agent to monitor the health of your
+Apache instance via the ``server-status`` URL, and to recover the instance if
+it fails. On both nodes, configure this URL as follows:
.. code-block:: none
# cat <<-END >/etc/httpd/conf.d/status.conf
SetHandler server-status
Require local
END
.. NOTE::
If you are using a different operating system, server-status may already be
enabled or may be configurable in a different location. If you are using
a version of Apache HTTP Server less than 2.4, the syntax will be different.
.. index::
pair: Apache HTTP Server; resource
Configure the Cluster
#####################
At this point, Apache is ready to go, and all that needs to be done is to
add it to the cluster. Let's call the resource WebSite. We need to use
-an OCF resource script called apache in the heartbeat namespace [#]_.
+an OCF resource agent called apache in the heartbeat namespace [#]_.
The script's only required parameter is the path to the main Apache
configuration file, and we'll tell the cluster to check once a
minute that Apache is still running.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource create WebSite ocf:heartbeat:apache \
configfile=/etc/httpd/conf/httpd.conf \
statusurl="http://localhost/server-status" \
op monitor interval=1min
-By default, the operation timeout for all resources' start, stop, and monitor
-operations is 20 seconds. In many cases, this timeout period is less than
-a particular resource's advised timeout period. For the purposes of this
+By default, the operation timeout for all resources' start, stop, monitor, and
+other operations is 20 seconds. In many cases, this timeout period is less than
+a particular resource's advised timeout period. For the purposes of this
tutorial, we will adjust the global operation timeout default to 240 seconds.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource op defaults update timeout=240s
Warning: Defaults do not apply to resources which override them with their own defined values
[root@pcmk-1 ~]# pcs resource op defaults
timeout: 240s
.. NOTE::
In a production cluster, it is usually better to adjust each resource's
- start, stop, and monitor timeouts to values that are appropriate to
- the behavior observed in your environment, rather than adjust
+ start, stop, and monitor timeouts to values that are appropriate for
+ the behavior observed in your environment, rather than adjusting
the global default.
+.. NOTE::
+
+ If you use a tool like ``pcs`` to create a resource, its operations may be
+ automatically configured with explicit timeout values that override the
+ Pacemaker built-in default value of 20 seconds. If the resource agent's
+ metadata contains suggested values for the operation timeouts in a
+ particular format, ``pcs`` reads those values and adds them to the
+ configuration at resource creation time.
+
After a short delay, we should see the cluster start Apache.
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:38:22 2021
* Last change: Tue Jan 26 19:38:19 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
* WebSite (ocf::heartbeat:apache): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Wait a moment, the WebSite resource isn't running on the same host as our
IP address!
.. NOTE::
If, in the ``pcs status`` output, you see the WebSite resource has
failed to start, then you've likely not enabled the status URL correctly.
You can check whether this is the problem by running:
.. code-block:: none
wget -O - http://localhost/server-status
If you see **Not Found** or **Forbidden** in the output, then this is likely the
problem. Ensure that the **** block is correct.
.. index::
single: constraint; colocation
single: colocation constraint
Ensure Resources Run on the Same Host
#####################################
To reduce the load on any one machine, Pacemaker will generally try to
spread the configured resources across the cluster nodes. However, we
can tell the cluster that two resources are related and need to run on
-the same host (or not at all). Here, we instruct the cluster that
-WebSite can only run on the host that ClusterIP is active on.
+the same host (or else one of them should not run at all, if they cannot run on
+the same node). Here, we instruct the cluster that WebSite can only run on the
+host where ClusterIP is active.
To achieve this, we use a *colocation constraint* that indicates it is
-mandatory for WebSite to run on the same node as ClusterIP. The
+mandatory for WebSite to run on the same node as ClusterIP. The
"mandatory" part of the colocation constraint is indicated by using a
-score of INFINITY. The INFINITY score also means that if ClusterIP is not
+score of INFINITY. The INFINITY score also means that if ClusterIP is not
active anywhere, WebSite will not be permitted to run.
.. NOTE::
If ClusterIP is not active anywhere, WebSite will not be permitted to run
anywhere.
+.. NOTE::
+
+ INFINITY is the default score for a colocation constraint. If you don't
+ specify a score, INFINITY will be used automatically.
+
.. IMPORTANT::
Colocation constraints are "directional", in that they imply certain
things about the order in which the two resources will have a location
chosen. In this case, we're saying that **WebSite** needs to be placed on the
same machine as **ClusterIP**, which implies that the cluster must know the
location of **ClusterIP** before choosing a location for **WebSite**.
.. code-block:: none
[root@pcmk-1 ~]# pcs constraint colocation add WebSite with ClusterIP INFINITY
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:45:11 2021
* Last change: Tue Jan 26 19:44:30 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
* WebSite (ocf::heartbeat:apache): Started pcmk-2
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
.. index::
single: constraint; ordering
single: ordering constraint
Ensure Resources Start and Stop in Order
########################################
Like many services, Apache can be configured to bind to specific
IP addresses on a host or to the wildcard IP address. If Apache
binds to the wildcard, it doesn't matter whether an IP address
is added before or after Apache starts; Apache will respond on
that IP just the same. However, if Apache binds only to certain IP
address(es), the order matters: If the address is added after Apache
starts, Apache won't respond on that address.
To be sure our WebSite responds regardless of Apache's address configuration,
we need to make sure ClusterIP not only runs on the same node,
-but starts before WebSite. A colocation constraint only ensures the
-resources run together, not the order in which they are started and stopped.
+but also starts before WebSite. A colocation constraint ensures only that the
+resources run together; it doesn't affect order in which the resources are
+started or stopped.
-We do this by adding an ordering constraint. By default, all order constraints
-are mandatory, which means that the recovery of ClusterIP will also trigger the
-recovery of WebSite.
+We do this by adding an ordering constraint. By default, all order constraints
+are mandatory. This means, for example, that if ClusterIP needs to stop, then
+WebSite must stop first (or already be stopped); and if WebSite needs to start,
+then ClusterIP must start first (or already be started). This also implies that
+the recovery of ClusterIP will trigger the recovery of WebSite, causing it to
+be restarted.
.. code-block:: none
[root@pcmk-1 ~]# pcs constraint order ClusterIP then WebSite
Adding ClusterIP WebSite (kind: Mandatory) (Options: first-action=start then-action=start)
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
+.. NOTE::
+
+ The default action in an order constraint is **start**. If you don't
+ specify an action, as in the example above, **pcs** automatically uses the
+ **start** action.
+
.. index::
single: constraint; location
single: location constraint
Prefer One Node Over Another
############################
Pacemaker does not rely on any sort of hardware symmetry between nodes,
so it may well be that one machine is more powerful than the other.
In such cases, you may want to host the resources on the more powerful node
when it is available, to have the best performance -- or you may want to host
the resources on the **less** powerful node when it's available, so you don't
have to worry about whether you can handle the load after a failover.
To do this, we create a location constraint.
In the location constraint below, we are saying the WebSite resource
prefers the node pcmk-1 with a score of 50. Here, the score indicates
how strongly we'd like the resource to run at this location.
.. code-block:: none
[root@pcmk-1 ~]# pcs constraint location WebSite prefers pcmk-1=50
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Resource: WebSite
Enabled on: pcmk-1 (score:50)
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:46:52 2021
* Last change: Tue Jan 26 19:46:40 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
* WebSite (ocf::heartbeat:apache): Started pcmk-2
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Wait a minute, the resources are still on pcmk-2!
Even though WebSite now prefers to run on pcmk-1, that preference is
(intentionally) less than the resource stickiness (how much we
preferred not to have unnecessary downtime).
To see the current placement scores, you can use a tool called crm_simulate.
.. code-block:: none
[root@pcmk-1 ~]# crm_simulate -sL
Current cluster status:
Online: [ pcmk-1 pcmk-2 ]
ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
WebSite (ocf::heartbeat:apache): Started pcmk-2
Allocation scores:
native_color: ClusterIP allocation score on pcmk-1: 50
native_color: ClusterIP allocation score on pcmk-2: 200
native_color: WebSite allocation score on pcmk-1: -INFINITY
native_color: WebSite allocation score on pcmk-2: 100
Transition Summary:
.. index::
single: resource; moving manually
Move Resources Manually
#######################
There are always times when an administrator needs to override the
cluster and force resources to move to a specific location. In this example,
we will force the WebSite to move to pcmk-1.
We will use the **pcs resource move** command to create a temporary constraint
with a score of INFINITY. While we could update our existing constraint,
using **move** allows to easily get rid of the temporary constraint later.
If desired, we could even give a lifetime for the constraint, so it would
expire automatically -- but we don't do that in this example.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource move WebSite pcmk-1
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Resource: WebSite
Enabled on: pcmk-1 (score:50)
Enabled on: pcmk-1 (score:INFINITY) (role: Started)
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:49:27 2021
* Last change: Tue Jan 26 19:49:10 2021 by root via crm_resource on pcmk-1
* 2 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Once we've finished whatever activity required us to move the
-resources to pcmk-1 (in our case nothing), we can then allow the cluster
-to resume normal operation by removing the new constraint. Due to our first
-location constraint and our default stickiness, the resources will remain on
-pcmk-1.
+resources to pcmk-1 (in our case nothing), the new constraint is no longer
+needed, and so we can remove it. Due to our first location constraint and our
+default stickiness, the resources will remain on pcmk-1.
We will use the **pcs resource clear** command, which removes all temporary
constraints previously created by **pcs resource move** or **pcs resource ban**.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource clear WebSite
Removing constraint: cli-prefer-WebSite
[root@pcmk-1 ~]# pcs constraint
Location Constraints:
Resource: WebSite
Enabled on: pcmk-1 (score:50)
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
Ticket Constraints:
Note that the INFINITY location constraint is now gone. If we check the cluster
status, we can also see that (as expected) the resources are still active
on pcmk-1.
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Tue Jan 26 19:50:52 2021
* Last change: Tue Jan 26 19:50:24 2021 by root via crm_resource on pcmk-1
* 2 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
To remove the constraint with the score of 50, we would first get the
-constraint's ID using **pcs constraint --full**, then remove it with
-**pcs constraint remove** and the ID. We won't show those steps here,
+constraint's ID using ``pcs constraint --full``, then remove it with
+``pcs constraint remove`` and the ID. We won't show those steps here,
but feel free to try it on your own, with the help of the pcs man page
if necessary.
.. [#] Compare the key used here, **ocf:heartbeat:apache**, with the one we
- used earlier for the IP address, **ocf:heartbeat:IPaddr2**
+ used earlier for the IP address, **ocf:heartbeat:IPaddr2**.
diff --git a/doc/sphinx/Clusters_from_Scratch/cluster-setup.rst b/doc/sphinx/Clusters_from_Scratch/cluster-setup.rst
index 8aeb39cfb0..13b7fed1f2 100644
--- a/doc/sphinx/Clusters_from_Scratch/cluster-setup.rst
+++ b/doc/sphinx/Clusters_from_Scratch/cluster-setup.rst
@@ -1,295 +1,296 @@
Set up a Cluster
----------------
Simplify Administration With a Cluster Shell
############################################
In the dark past, configuring Pacemaker required the administrator to
read and write XML. In true UNIX style, there were also a number of
different commands that specialized in different aspects of querying
and updating the cluster.
In addition, the various components of the cluster stack (corosync, pacemaker,
etc.) had to be configured separately, with different configuration tools and
formats.
All of that has been greatly simplified with the creation of higher-level tools,
whether command-line or GUIs, that hide all the mess underneath.
Command-line cluster shells take all the individual aspects required for
managing and configuring a cluster, and pack them into one simple-to-use
command-line tool.
They even allow you to queue up several changes at once and commit
them all at once.
Two popular command-line shells are ``pcs`` and ``crmsh``. Clusters from Scratch is
based on ``pcs`` because it comes with CentOS, but both have similar
functionality. Choosing a shell or GUI is a matter of personal preference and
what comes with (and perhaps is supported by) your choice of operating system.
Install the Cluster Software
############################
Fire up a shell on both nodes and run the following to activate the High
Availability repo.
.. code-block:: none
# dnf config-manager --set-enabled ha
.. IMPORTANT::
This document will show commands that need to be executed on both nodes
with a simple ``#`` prompt. Be sure to run them on each node individually.
Now, we'll install pacemaker, pcs, and some other command-line tools that will
make our lives easier:
.. code-block:: none
# yum install -y pacemaker pcs psmisc policycoreutils-python3
.. NOTE::
This document uses ``pcs`` for cluster management. Other alternatives,
such as ``crmsh``, are available, but their syntax
will differ from the examples used here.
Configure the Cluster Software
##############################
.. index::
single: firewall
Allow cluster services through firewall
_______________________________________
On each node, allow cluster-related services through the local firewall:
.. code-block:: none
# firewall-cmd --permanent --add-service=high-availability
success
# firewall-cmd --reload
success
.. NOTE ::
If you are using iptables directly, or some other firewall solution besides
firewalld, simply open the following ports, which can be used by various
clustering components: TCP ports 2224, 3121, and 21064, and UDP port 5405.
If you run into any problems during testing, you might want to disable
the firewall and SELinux entirely until you have everything working.
This may create significant security issues and should not be performed on
machines that will be exposed to the outside world, but may be appropriate
during development and testing on a protected host.
To disable security measures:
.. code-block:: none
[root@pcmk-1 ~]# setenforce 0
[root@pcmk-1 ~]# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config
[root@pcmk-1 ~]# systemctl mask firewalld.service
[root@pcmk-1 ~]# systemctl stop firewalld.service
[root@pcmk-1 ~]# iptables --flush
Enable pcs Daemon
_________________
Before the cluster can be configured, the pcs daemon must be started and enabled
to start at boot time on each node. This daemon works with the pcs command-line interface
-to manage synchronizing the corosync configuration across all nodes in the cluster.
+to manage synchronizing the corosync configuration across all nodes in the
+cluster, among other functions.
Start and enable the daemon by issuing the following commands on each node:
.. code-block:: none
# systemctl start pcsd.service
# systemctl enable pcsd.service
Created symlink from /etc/systemd/system/multi-user.target.wants/pcsd.service to /usr/lib/systemd/system/pcsd.service.
-The installed packages will create a **hacluster** user with a disabled password.
+The installed packages will create an **hacluster** user with a disabled password.
While this is fine for running ``pcs`` commands locally,
the account needs a login password in order to perform such tasks as syncing
the corosync configuration, or starting and stopping the cluster on other nodes.
This tutorial will make use of such commands,
so now we will set a password for the **hacluster** user, using the same password
on both nodes:
.. code-block:: none
# passwd hacluster
Changing password for user hacluster.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
.. NOTE::
Alternatively, to script this process or set the password on a
different machine from the one you're logged into, you can use
the ``--stdin`` option for ``passwd``:
.. code-block:: none
[root@pcmk-1 ~]# ssh pcmk-2 -- 'echo mysupersecretpassword | passwd --stdin hacluster'
Configure Corosync
__________________
On either node, use ``pcs host auth`` to authenticate as the **hacluster** user:
.. code-block:: none
[root@pcmk-1 ~]# pcs host auth pcmk-1 pcmk-2
Username: hacluster
Password:
pcmk-2: Authorized
pcmk-1: Authorized
Next, use ``pcs cluster setup`` on the same node to generate and synchronize the
corosync configuration:
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster setup mycluster pcmk-1 pcmk-2
No addresses specified for host 'pcmk-1', using 'pcmk-1'
No addresses specified for host 'pcmk-2', using 'pcmk-2'
Destroying cluster on hosts: 'pcmk-1', 'pcmk-2'...
pcmk-2: Successfully destroyed cluster
pcmk-1: Successfully destroyed cluster
Requesting remove 'pcsd settings' from 'pcmk-1', 'pcmk-2'
pcmk-1: successful removal of the file 'pcsd settings'
pcmk-2: successful removal of the file 'pcsd settings'
Sending 'corosync authkey', 'pacemaker authkey' to 'pcmk-1', 'pcmk-2'
pcmk-1: successful distribution of the file 'corosync authkey'
pcmk-1: successful distribution of the file 'pacemaker authkey'
pcmk-2: successful distribution of the file 'corosync authkey'
pcmk-2: successful distribution of the file 'pacemaker authkey'
Sending 'corosync.conf' to 'pcmk-1', 'pcmk-2'
pcmk-1: successful distribution of the file 'corosync.conf'
pcmk-2: successful distribution of the file 'corosync.conf'
Cluster has been successfully set up.
If you received an authorization error for either of those commands, make
sure you configured the **hacluster** user account on each node
with the same password.
The final corosync.conf configuration on each node should look
something like the sample in :ref:`sample-corosync-configuration`.
Explore pcs
###########
Start by taking some time to familiarize yourself with what ``pcs`` can do.
.. code-block:: none
[root@pcmk-1 ~]# pcs
Usage: pcs [-f file] [-h] [commands]...
Control and configure pacemaker and corosync.
Options:
-h, --help Display usage and exit.
-f file Perform actions on file instead of active CIB.
Commands supporting the option use the initial state of
the specified file as their input and then overwrite the
file with the state reflecting the requested
operation(s).
A few commands only use the specified file in read-only
mode since their effect is not a CIB modification.
--debug Print all network traffic and external commands run.
--version Print pcs version information. List pcs capabilities if
--full is specified.
--request-timeout Timeout for each outgoing request to another node in
seconds. Default is 60s.
--force Override checks and errors, the exact behavior depends on
the command. WARNING: Using the --force option is
strongly discouraged unless you know what you are doing.
Commands:
cluster Configure cluster options and nodes.
resource Manage cluster resources.
stonith Manage fence devices.
constraint Manage resource constraints.
property Manage pacemaker properties.
acl Manage pacemaker access control lists.
qdevice Manage quorum device provider on the local host.
quorum Manage cluster quorum settings.
booth Manage booth (cluster ticket manager).
status View cluster status.
config View and manage cluster configuration.
pcsd Manage pcs daemon.
host Manage hosts known to pcs/pcsd.
node Manage cluster nodes.
alert Manage pacemaker alerts.
client Manage pcsd client configuration.
dr Manage disaster recovery configuration.
tag Manage pacemaker tags.
As you can see, the different aspects of cluster management are separated
into categories. To discover the functionality available in each of these
categories, one can issue the command ``pcs help``. Below is an
example of all the options available under the status category.
.. code-block:: none
[root@pcmk-1 ~]# pcs status help
Usage: pcs status [commands]...
View current cluster and resource status
Commands:
[status] [--full] [--hide-inactive]
View all information about the cluster and resources (--full provides
more details, --hide-inactive hides inactive resources).
resources [--hide-inactive]
Show status of all currently configured resources. If --hide-inactive
is specified, only show active resources.
cluster
View current cluster status.
corosync
View current membership information as seen by corosync.
quorum
View current quorum status.
qdevice [--full] []
Show runtime status of specified model of quorum device provider. Using
--full will give more detailed output. If is specified,
only information about the specified cluster will be displayed.
booth
Print current status of booth on the local node.
nodes [corosync | both | config]
View current status of nodes from pacemaker. If 'corosync' is
specified, view current status of nodes from corosync instead. If
'both' is specified, view current status of nodes from both corosync &
pacemaker. If 'config' is specified, print nodes from corosync &
pacemaker configuration.
pcsd []...
Show current status of pcsd on nodes specified, or on all nodes
configured in the local cluster if no nodes are specified.
xml
View xml version of status (output from crm_mon -r -1 -X).
Additionally, if you are interested in the version and supported cluster stack(s)
available with your Pacemaker installation, run:
.. code-block:: none
[root@pcmk-1 ~]# pacemakerd --features
Pacemaker 2.0.5-4.el8 (Build: ba59be7122)
Supporting v3.6.1: generated-manpages agent-manpages ncurses libqb-logging libqb-ipc systemd nagios corosync-native atomic-attrd acls cibsecrets
diff --git a/doc/sphinx/Clusters_from_Scratch/fencing.rst b/doc/sphinx/Clusters_from_Scratch/fencing.rst
index 14fe088b06..b45919e45f 100644
--- a/doc/sphinx/Clusters_from_Scratch/fencing.rst
+++ b/doc/sphinx/Clusters_from_Scratch/fencing.rst
@@ -1,237 +1,240 @@
.. index:: fencing
Configure Fencing
-----------------
What is Fencing?
################
Fencing protects your data from being corrupted, and your application from
becoming unavailable, due to unintended concurrent access by rogue nodes.
Just because a node is unresponsive doesn't mean it has stopped
accessing your data. The only way to be 100% sure that your data is
safe, is to use fencing to ensure that the node is truly
offline before allowing the data to be accessed from another node.
Fencing also has a role to play in the event that a clustered service
cannot be stopped. In this case, the cluster uses fencing to force the
whole node offline, thereby making it safe to start the service
elsewhere.
Fencing is also known as STONITH, an acronym for "Shoot The Other Node In The
Head", since the most popular form of fencing is cutting a host's power.
In order to guarantee the safety of your data [#]_, fencing is enabled by default.
.. NOTE::
It is possible to tell the cluster not to use fencing, by setting the
- **stonith-enabled** cluster option to false:
+ **stonith-enabled** cluster property to false:
.. code-block:: none
[root@pcmk-1 ~]# pcs property set stonith-enabled=false
[root@pcmk-1 ~]# crm_verify -L
However, this is completely inappropriate for a production cluster. It tells
the cluster to simply pretend that failed nodes are safely powered off. Some
vendors will refuse to support clusters that have fencing disabled. Even
disabling it for a test cluster means you won't be able to test real failure
scenarios.
.. index::
single: fencing; device
Choose a Fence Device
#####################
The two broad categories of fence device are power fencing, which cuts off
power to the target, and fabric fencing, which cuts off the target's access to
some critical resource, such as a shared disk or access to the local network.
Power fencing devices include:
* Intelligent power switches
* IPMI
* Hardware watchdog device (alone, or in combination with shared storage used
as a "poison pill" mechanism)
Fabric fencing devices include:
* Shared storage that can be cut off for a target host by another host (for
example, an external storage device that supports SCSI-3 persistent
reservations)
* Intelligent network switches
Using IPMI as a power fencing device may seem like a good choice. However,
if the IPMI shares power and/or network access with the host (such as most
onboard IPMI controllers), a power or network failure will cause both the
host and its fencing device to fail. The cluster will be unable to recover,
and must stop all resources to avoid a possible split-brain situation.
Likewise, any device that relies on the machine being active (such as
SSH-based "devices" sometimes used during testing) is inappropriate,
because fencing will be required when the node is completely unresponsive.
+(Fence agents like ``fence_ilo_ssh``, which connects via SSH to an HP iLO but
+not to the cluster node, are fine.)
Configure the Cluster for Fencing
#################################
#. Install the fence agent(s). To see what packages are available, run
``yum search fence-``. Be sure to install the package(s) on all cluster nodes.
#. Configure the fence device itself to be able to fence your nodes and accept
fencing requests. This includes any necessary configuration on the device and
on the nodes, and any firewall or SELinux changes needed. Test the
communication between the device and your nodes.
#. Find the name of the correct fence agent: ``pcs stonith list``
#. Find the parameters associated with the device:
``pcs stonith describe ``
#. Create a local copy of the CIB: ``pcs cluster cib stonith_cfg``
#. Create the fencing resource: ``pcs -f stonith_cfg stonith create [STONITH_DEVICE_OPTIONS]``
Any flags that do not take arguments, such as ``--ssl``, should be passed as ``ssl=1``.
-#. Enable fencing in the cluster: ``pcs -f stonith_cfg property set stonith-enabled=true``
+#. Ensure fencing is enabled in the cluster:
+ ``pcs -f stonith_cfg property set stonith-enabled=true``
#. If the device does not know how to fence nodes based on their cluster node
name, you may also need to set the special **pcmk_host_map** parameter. See
``man pacemaker-fenced`` for details.
#. If the device does not support the **list** command, you may also need
to set the special **pcmk_host_list** and/or **pcmk_host_check**
parameters. See ``man pacemaker-fenced`` for details.
#. If the device does not expect the victim to be specified with the
**port** parameter, you may also need to set the special
**pcmk_host_argument** parameter. See ``man pacemaker-fenced`` for details.
#. Commit the new configuration: ``pcs cluster cib-push stonith_cfg``
#. Once the fence device resource is running, test it (you might want to stop
the cluster on that machine first):
``stonith_admin --reboot ``
Example
#######
For this example, assume we have a chassis containing four nodes
and a separately powered IPMI device active on 10.0.0.1. Following the steps
above would go something like this:
Step 1: Install the **fence-agents-ipmilan** package on both nodes.
Step 2: Configure the IP address, authentication credentials, etc. in the IPMI device itself.
Step 3: Choose the **fence_ipmilan** STONITH agent.
Step 4: Obtain the agent's possible parameters:
.. code-block:: none
[root@pcmk-1 ~]# pcs stonith describe fence_ipmilan
fence_ipmilan - Fence agent for IPMI
fence_ipmilan is an I/O Fencing agentwhich can be used with machines controlled by IPMI.This agent calls support software ipmitool (http://ipmitool.sf.net/). WARNING! This fence agent might report success before the node is powered off. You should use -m/method onoff if your fence device works correctly with that option.
Stonith options:
auth: IPMI Lan Auth type.
cipher: Ciphersuite to use (same as ipmitool -C parameter)
hexadecimal_kg: Hexadecimal-encoded Kg key for IPMIv2 authentication
ip: IP address or hostname of fencing device
ipport: TCP/UDP port to use for connection with device
lanplus: Use Lanplus to improve security of connection
method: Method to fence
password: Login password or passphrase
password_script: Script to run to retrieve password
plug: IP address or hostname of fencing device (together with --port-as-ip)
privlvl: Privilege level on IPMI device
target: Bridge IPMI requests to the remote target address
username: Login name
quiet: Disable logging to stderr. Does not affect --verbose or --debug-file or logging to syslog.
verbose: Verbose mode. Multiple -v flags can be stacked on the command line (e.g., -vvv) to increase
verbosity.
verbose_level: Level of debugging detail in output. Defaults to the number of --verbose flags specified
on the command line, or to 1 if verbose=1 in a stonith device configuration (i.e., on
stdin).
debug_file: Write debug information to given file
delay: Wait X seconds before fencing is started
disable_timeout: Disable timeout (true/false) (default: true when run from Pacemaker 2.0+)
ipmitool_path: Path to ipmitool binary
login_timeout: Wait X seconds for cmd prompt after login
port_as_ip: Make "port/plug" to be an alias to IP address
power_timeout: Test X seconds for status change after ON/OFF
power_wait: Wait X seconds after issuing ON/OFF
shell_timeout: Wait X seconds for cmd prompt after issuing command
retry_on: Count of attempts to retry power on
use_sudo: Use sudo (without password) when calling 3rd party software
sudo_path: Path to sudo binary
pcmk_host_map: A mapping of host names to ports numbers for devices that do not support host names. Eg.
node1:1;node2:2,3 would tell the cluster to use port 1 for node1 and ports 2 and 3 for
node2
pcmk_host_list: A list of machines controlled by this device (Optional unless pcmk_host_check=static-
list).
pcmk_host_check: How to determine which machines are controlled by the device. Allowed values: dynamic-
list (query the device via the 'list' command), static-list (check the pcmk_host_list
attribute), status (query the device via the 'status' command), none (assume every
device can fence every machine)
pcmk_delay_max: Enable a random delay for stonith actions and specify the maximum of random delay. This
prevents double fencing when using slow devices such as sbd. Use this to enable a
random delay for stonith actions. The overall delay is derived from this random delay
value adding a static delay so that the sum is kept below the maximum delay.
pcmk_delay_base: Enable a base delay for stonith actions and specify base delay value. This prevents
double fencing when different delays are configured on the nodes. Use this to enable a
static delay for stonith actions. The overall delay is derived from a random delay
value adding this static delay so that the sum is kept below the maximum delay.
pcmk_action_limit: The maximum number of actions can be performed in parallel on this device Cluster
property concurrent-fencing=true needs to be configured first. Then use this to
specify the maximum number of actions can be performed in parallel on this device.
-1 is unlimited.
Default operations:
monitor: interval=60s
Step 5: ``pcs cluster cib stonith_cfg``
Step 6: Here are example parameters for creating our fence device resource:
.. code-block:: none
[root@pcmk-1 ~]# pcs -f stonith_cfg stonith create ipmi-fencing fence_ipmilan \
pcmk_host_list="pcmk-1 pcmk-2" ipaddr=10.0.0.1 login=testuser \
passwd=acd123 op monitor interval=60s
[root@pcmk-1 ~]# pcs -f stonith_cfg stonith
* ipmi-fencing (stonith:fence_ipmilan): Stopped
Steps 7-10: Enable fencing in the cluster:
.. code-block:: none
[root@pcmk-1 ~]# pcs -f stonith_cfg property set stonith-enabled=true
[root@pcmk-1 ~]# pcs -f stonith_cfg property
Cluster Properties:
cluster-infrastructure: corosync
cluster-name: mycluster
dc-version: 2.0.5-4.el8-ba59be7122
have-watchdog: false
stonith-enabled: true
Step 11: ``pcs cluster cib-push stonith_cfg --config``
Step 12: Test:
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster stop pcmk-2
[root@pcmk-1 ~]# stonith_admin --reboot pcmk-2
After a successful test, login to any rebooted nodes, and start the cluster
(with ``pcs cluster start``).
.. [#] If the data is corrupt, there is little point in continuing to
make it available.
diff --git a/doc/sphinx/Clusters_from_Scratch/index.rst b/doc/sphinx/Clusters_from_Scratch/index.rst
index f9546cf018..74fe2503af 100644
--- a/doc/sphinx/Clusters_from_Scratch/index.rst
+++ b/doc/sphinx/Clusters_from_Scratch/index.rst
@@ -1,49 +1,49 @@
Clusters from Scratch
=====================
*Step-by-Step Instructions for Building Your First High-Availability Cluster*
Abstract
--------
This document provides a step-by-step guide to building a simple high-availability
cluster using Pacemaker.
The example cluster will use:
* |CFS_DISTRO| |CFS_DISTRO_VER| as the host operating system
-* Corosync to provide messaging and membership services,
-* Pacemaker 2
-* DRBD as a cost-effective alternative to shared storage,
+* Corosync to provide messaging and membership services
+* Pacemaker 2 as the cluster resource manager
+* DRBD as a cost-effective alternative to shared storage
* GFS2 as the cluster filesystem (in active/active mode)
Given the graphical nature of the install process, a number of screenshots are
-included. However the guide is primarily composed of commands, the reasons for
-executing them and their expected outputs.
+included. However, the guide is primarily composed of commands, the reasons for
+executing them, and their expected outputs.
Table of Contents
-----------------
.. toctree::
:maxdepth: 3
:numbered:
intro
installation
cluster-setup
verification
fencing
active-passive
apache
shared-storage
active-active
ap-configuration
ap-corosync-conf
ap-reading
Index
-----
* :ref:`genindex`
* :ref:`search`
diff --git a/doc/sphinx/Clusters_from_Scratch/installation.rst b/doc/sphinx/Clusters_from_Scratch/installation.rst
index c0e9c55bd4..565f8fe7f0 100644
--- a/doc/sphinx/Clusters_from_Scratch/installation.rst
+++ b/doc/sphinx/Clusters_from_Scratch/installation.rst
@@ -1,424 +1,431 @@
Installation
------------
Install |CFS_DISTRO| |CFS_DISTRO_VER|
################################################################################################
Boot the Install Image
______________________
Download the latest |CFS_DISTRO| |CFS_DISTRO_VER| DVD ISO by navigating to
the `CentOS Mirrors List `_,
selecting a download mirror which is close to you, and finally selecting the
.iso file that has "dvd" in its name.
Use the image to boot a virtual machine, or burn it to a DVD or USB drive and
boot a physical server from that.
After starting the installation, select your language and keyboard layout at
the welcome screen.
.. figure:: images/WelcomeToCentos.png
:align: center
:alt: Installation Welcome Screen
|CFS_DISTRO| |CFS_DISTRO_VER| Installation Welcome Screen
Installation Options
____________________
At this point, you get a chance to tweak the default installation options.
.. figure:: images/InstallationSummary.png
:align: center
:alt: Installation Summary Screen
|CFS_DISTRO| |CFS_DISTRO_VER| Installation Summary Screen
Click on the **SOFTWARE SELECTION** section (try saying that 10 times quickly). The
default environment, **Server with GUI**, does have add-ons with much of the software
we need, but we will change the environment to a **Minimal Install** here, so that we
can see exactly what software is required later, and press **Done**.
.. figure:: images/SoftwareSelection.png
:align: center
:alt: Software Selection Screen
|CFS_DISTRO| |CFS_DISTRO_VER| Software Selection Screen
Configure Network
_________________
-In the **NETWORK & HOSTNAME** section:
+In the **NETWORK & HOST NAME** section:
- Edit **Host Name:** as desired. For this example, we will use
**pcmk-1.localdomain** and then press **Apply**.
-- Select your network device, press **Configure...**, and use the **Manual** method to
- assign a fixed IP address. For this example, we'll use 192.168.122.101 under
- **IPv4 Settings** (with an appropriate netmask, gateway and DNS server).
+- Select your network device, press **Configure...**, select the **IPv4
+ Settings** tab, and select **Manual** from the **Method** dropdown menu. Then
+ assign the machine a fixed IP address with an appropriate netmask, gateway,
+ and DNS server. For this example, we'll use **192.168.122.101** for the
+ address, **24** for the netmask, and **192.168.122.1** for the gateway and
+ DNS server.
- Press **Save**.
- Flip the switch to turn your network device on, and press **Done**.
.. figure:: images/NetworkAndHostName.png
:align: center
:alt: Editing network settings
|CFS_DISTRO| |CFS_DISTRO_VER| Network Interface Screen
.. IMPORTANT::
Do not accept the default network settings.
Cluster machines should never obtain an IP address via DHCP, because
DHCP's periodic address renewal will interfere with corosync.
Configure Disk
______________
By default, the installer's automatic partitioning will use LVM (which allows
us to dynamically change the amount of space allocated to a given partition).
-However, it allocates all free space to the ``/`` (aka. **root**) partition, which
-cannot be reduced in size later (dynamic increases are fine).
+However, it allocates all free space to the ``/`` (a.k.a. **root**) partition,
+which cannot be reduced in size later (dynamic increases are fine).
In order to follow the DRBD and GFS2 portions of this guide, we need to reserve
space on each machine for a replicated volume.
-Enter the **INSTALLATION DESTINATION** section, ensure the hard drive you want to
-install to is selected, select **Custom** to be the **Storage Configuration**, and
-press **Done**.
+Enter the **INSTALLATION DESTINATION** section and select the disk where you
+want to install the OS. Then under **Storage Configuration**, select **Custom**
+and press **Done**.
-In the **MANUAL PARTITIONING** screen that comes next, click the option to create
-mountpoints automatically. Select the ``/`` mountpoint, and reduce the desired
-capacity by 3GiB or so. Select **Modify...** by the volume group name, and change
-the **Size policy:** to **As large as possible**, to make the reclaimed space
-available inside the LVM volume group. We'll add the additional volume later.
+On the **MANUAL PARTITIONING** screen that comes next, click the option to create
+mountpoints automatically. Select the ``/`` mountpoint and reduce the **Desired
+Capacity** down to 4 GiB or so. (The installer will not allow you to proceed if
+the / filesystem is too small to install all required packages.) Then select
+**Modify…** next to the volume group name, and change the **Size policy** to
+**As large as possible**, to make the reclaimed space available inside the LVM
+volume group. We’ll add the additional volume later.
.. figure:: images/ManualPartitioning.png
:align: center
:alt: Manual Partitioning Screen
|CFS_DISTRO| |CFS_DISTRO_VER| Manual Partitioning Screen
Press **Done**, then **Accept changes**.
Configure Time Synchronization
______________________________
It is highly recommended to enable NTP on your cluster nodes. Doing so
ensures all nodes agree on the current time and makes reading log files
significantly easier.
|CFS_DISTRO| will enable NTP automatically. If you want to change any time-related
settings (such as time zone or NTP server), you can do this in the
**TIME & DATE** section.
Root Password
______________________________
In order to continue to the next step, a **Root Password** must be set.
.. figure:: images/RootPassword.png
:align: center
:alt: Root Password Screen
|CFS_DISTRO| |CFS_DISTRO_VER| Root Password Screen
-Press **Done** (depending on the password you chose, you may need to do so twice).
+Press **Done**. (Depending on the password you chose, you may need to do so
+twice.)
Finish Install
______________
Select **Begin Installation**. Once it completes, **Reboot System**
as instructed. After the node reboots, you'll see a login prompt on
the console. Login using **root** and the password you created earlier.
.. figure:: images/ConsolePrompt.png
:align: center
:alt: Console Prompt
|CFS_DISTRO| |CFS_DISTRO_VER| Console Prompt
.. NOTE::
From here on, we're going to be working exclusively from the terminal.
Configure the OS
################
Verify Networking
_________________
Ensure that the machine has the static IP address you configured earlier.
.. code-block:: none
[root@pcmk-1 ~]# ip addr
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp1s0: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:32:cf:a9 brd ff:ff:ff:ff:ff:ff
inet 192.168.122.101/24 brd 192.168.122.255 scope global noprefixroute enp1s0
valid_lft forever preferred_lft forever
inet6 fe80::c3e1:3ba:959:fa96/64 scope link noprefixroute
valid_lft forever preferred_lft forever
.. NOTE::
If you ever need to change the node's IP address from the command line, follow
these instructions, replacing **${device}** with the name of your network device:
.. code-block:: none
[root@pcmk-1 ~]# vi /etc/sysconfig/network-scripts/ifcfg-${device} # manually edit as desired
[root@pcmk-1 ~]# nmcli dev disconnect ${device}
[root@pcmk-1 ~]# nmcli con reload ${device}
[root@pcmk-1 ~]# nmcli con up ${device}
This makes **NetworkManager** aware that a change was made on the config file.
Next, ensure that the routes are as expected:
.. code-block:: none
[root@pcmk-1 ~]# ip route
default via 192.168.122.1 dev enp1s0 proto static metric 100
192.168.122.0/24 dev enp1s0 proto kernel scope link src 192.168.122.101 metric 100
If there is no line beginning with **default via**, then you may need to add a line such as
``GATEWAY="192.168.122.1"``
to the device configuration using the same process as described above for
changing the IP address.
Now, check for connectivity to the outside world. Start small by
testing whether we can reach the gateway we configured.
.. code-block:: none
[root@pcmk-1 ~]# ping -c 1 192.168.122.1
PING 192.168.122.1 (192.168.122.1) 56(84) bytes of data.
64 bytes from 192.168.122.1: icmp_seq=1 ttl=64 time=0.492 ms
--- 192.168.122.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.492/0.492/0.492/0.000 ms
Now try something external; choose a location you know should be available.
.. code-block:: none
[root@pcmk-1 ~]# ping -c 1 www.clusterlabs.org
PING mx1.clusterlabs.org (95.217.104.78) 56(84) bytes of data.
64 bytes from mx1.clusterlabs.org (95.217.104.78): icmp_seq=1 ttl=54 time=134 ms
--- mx1.clusterlabs.org ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 133.987/133.987/133.987/0.000 ms
Login Remotely
______________
The console isn't a very friendly place to work from, so we will now
switch to accessing the machine remotely via SSH where we can
use copy and paste, etc.
From another host, check whether we can see the new host at all:
.. code-block:: none
[gchin@gchin ~]$ ping -c 1 192.168.122.101
PING 192.168.122.101 (192.168.122.101) 56(84) bytes of data.
64 bytes from 192.168.122.101: icmp_seq=1 ttl=64 time=0.344 ms
--- 192.168.122.101 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.344/0.344/0.344/0.000 ms
Next, login as root via SSH.
.. code-block:: none
[gchin@gchin ~]$ ssh root@192.168.122.101
The authenticity of host '192.168.122.101 (192.168.122.101)' can't be established.
ECDSA key fingerprint is SHA256:NBvcRrPDLIt39Rf0Tz4/f2Rd/FA5wUiDOd9bZ9QWWjo.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '192.168.122.101' (ECDSA) to the list of known hosts.
root@192.168.122.101's password:
Last login: Tue Jan 10 20:46:30 2021
[root@pcmk-1 ~]#
Apply Updates
_____________
Apply any package updates released since your installation image was created:
.. code-block:: none
[root@pcmk-1 ~]# yum update
.. index::
single: node; short name
Use Short Node Names
____________________
During installation, we filled in the machine's fully qualified domain
name (FQDN), which can be rather long when it appears in cluster logs and
status output. See for yourself how the machine identifies itself:
.. code-block:: none
[root@pcmk-1 ~]# uname -n
pcmk-1.localdomain
We can use the `hostnamectl` tool to strip off the domain name:
.. code-block:: none
[root@pcmk-1 ~]# hostnamectl set-hostname $(uname -n | sed s/\\..*//)
Now, check that the machine is using the correct name:
.. code-block:: none
[root@pcmk-1 ~]# uname -n
pcmk-1
You may want to reboot to ensure all updates take effect.
Repeat for Second Node
######################
-Repeat the Installation steps so far, so that you have two
+Repeat the installation steps so far, so that you have two
nodes ready to have the cluster software installed.
For the purposes of this document, the additional node is called
pcmk-2 with address 192.168.122.102.
Configure Communication Between Nodes
#####################################
Configure Host Name Resolution
______________________________
Confirm that you can communicate between the two new nodes:
.. code-block:: none
[root@pcmk-1 ~]# ping -c 3 192.168.122.102
PING 192.168.122.102 (192.168.122.102) 56(84) bytes of data.
64 bytes from 192.168.122.102: icmp_seq=1 ttl=64 time=1.22 ms
64 bytes from 192.168.122.102: icmp_seq=2 ttl=64 time=0.795 ms
64 bytes from 192.168.122.102: icmp_seq=3 ttl=64 time=0.751 ms
--- 192.168.122.102 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2054ms
rtt min/avg/max/mdev = 0.751/0.923/1.224/0.214 ms
Now we need to make sure we can communicate with the machines by their
name. If you have a DNS server, add additional entries for the two
machines. Otherwise, you'll need to add the machines to ``/etc/hosts``
-on both nodes. Below are the entries for my cluster nodes:
+on both nodes. The entries for your cluster nodes should look something like
+the following:
.. code-block:: none
[root@pcmk-1 ~]# grep pcmk /etc/hosts
192.168.122.101 pcmk-1.clusterlabs.org pcmk-1
192.168.122.102 pcmk-2.clusterlabs.org pcmk-2
We can now verify the setup by again using ping:
.. code-block:: none
[root@pcmk-1 ~]# ping -c 3 pcmk-2
PING pcmk-2.clusterlabs.org (192.168.122.102) 56(84) bytes of data.
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=1 ttl=64 time=0.295 ms
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=2 ttl=64 time=0.616 ms
64 bytes from pcmk-2.clusterlabs.org (192.168.122.102): icmp_seq=3 ttl=64 time=0.809 ms
--- pcmk-2.clusterlabs.org ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2043ms
rtt min/avg/max/mdev = 0.295/0.573/0.809/0.212 ms
.. index:: SSH
Configure SSH
_____________
SSH is a convenient and secure way to copy files and perform commands
remotely. For the purposes of this guide, we will create a key without a
password (using the -N option) so that we can perform remote actions
without being prompted.
.. WARNING::
Unprotected SSH keys (those without a password) are not recommended for
servers exposed to the outside world. We use them here only to simplify
the demo.
Create a new key and allow anyone with that key to log in:
.. index::
single: SSH; key
.. topic:: Creating and Activating a New SSH Key
.. code-block:: none
[root@pcmk-1 ~]# ssh-keygen -f ~/.ssh/id_rsa -N ""
Generating public/private rsa key pair.
Your identification has been saved in /root/.ssh/id_rsa
Your public key has been saved in /root/.ssh/id_rsa.pub
The key fingerprint is:
SHA256:h5AFPmXsGU4woOxRLYHW9lnU2wIQVOxpSRrsXbo/AX8 root@pcmk-1
The key's randomart image is:
+---[RSA 3072]----+
| o+*BX*. |
| .oo+.+*O o |
| .+. +=% O o |
| . . =o%.o . |
| . .S+.. |
| ..o E |
| . o |
| o |
| . |
+----[SHA256]-----+
[root@pcmk-1 ~]# cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
Install the key on the other node:
.. code-block:: none
[root@pcmk-1 ~]# ssh-copy-id pcmk-2
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
The authenticity of host 'pcmk-2 (192.168.122.102)' can't be established.
ED25519 key fingerprint is SHA256:QkJnJ3fmszY7kAuuZ7wxUC5CC+eQThSCF13XYWnZJPo.
This host key is known by the following other names/addresses:
~/.ssh/known_hosts:1: 192.168.122.102
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@pcmk-2's password:
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'pcmk-2'"
and check to make sure that only the key(s) you wanted were added.
Test that you can now run commands remotely, without being prompted:
.. code-block:: none
[root@pcmk-1 ~]# ssh pcmk-2 -- uname -n
pcmk-2
Finally, repeat this same process on the other node. For convenience, you can
also generate an SSH key on your administrative machine and use **ssh-copy-id**
to copy it to both cluster nodes.
diff --git a/doc/sphinx/Clusters_from_Scratch/intro.rst b/doc/sphinx/Clusters_from_Scratch/intro.rst
index fb0de2816a..ecd192c567 100644
--- a/doc/sphinx/Clusters_from_Scratch/intro.rst
+++ b/doc/sphinx/Clusters_from_Scratch/intro.rst
@@ -1,29 +1,29 @@
Introduction
------------
-The Scope of this Document
+The Scope of This Document
##########################
Computer clusters can be used to provide highly available services or
resources. The redundancy of multiple machines is used to guard
against failures of many types.
This document will walk through the installation and setup of simple
clusters using the |CFS_DISTRO| distribution, version |CFS_DISTRO_VER|.
The clusters described here will use Pacemaker and Corosync to provide
resource management and messaging. Required packages and modifications
to their configuration files are described along with the use of the
-Pacemaker command line tool for generating the XML used for cluster
+**pcs** command line tool for generating the XML used for cluster
control.
Pacemaker is a central component and provides the resource management
required in these systems. This management includes detecting and
-recovering from the failure of various nodes, resources and services
+recovering from the failure of various nodes, resources, and services
under its control.
When more in-depth information is required, and for real-world usage,
please refer to the `Pacemaker Explained `_
manual.
.. include:: ../shared/pacemaker-intro.rst
diff --git a/doc/sphinx/Clusters_from_Scratch/shared-storage.rst b/doc/sphinx/Clusters_from_Scratch/shared-storage.rst
index 4ed84ece19..b719fc87bd 100644
--- a/doc/sphinx/Clusters_from_Scratch/shared-storage.rst
+++ b/doc/sphinx/Clusters_from_Scratch/shared-storage.rst
@@ -1,621 +1,621 @@
.. index::
pair: storage; DRBD
Replicate Storage Using DRBD
----------------------------
Even if you're serving up static websites, having to manually synchronize
the contents of that website to all the machines in the cluster is not
ideal. For dynamic websites, such as a wiki, it's not even an option. Not
everyone can afford network-attached storage, but somehow the data needs
to be kept in sync.
Enter DRBD, which can be thought of as network-based RAID-1 [#]_.
Install the DRBD Packages
#########################
DRBD itself is included in the upstream kernel [#]_, but we do need some
utilities to use it effectively.
CentOS does not ship these utilities, so we need to enable a third-party
repository to get them. Supported packages for many OSes are available from
DRBD's maker `LINBIT `_, but here we'll use the free
`ELRepo `_ repository.
On both nodes, import the ELRepo package signing key, and enable the
repository:
.. code-block:: none
# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
# rpm -Uvh https://www.elrepo.org/elrepo-release-8.el8.elrepo.noarch.rpm
Retrieving https://www.elrepo.org/elrepo-release-8.el8.elrepo.noarch.rpm
Verifying... ################################# [100%]
Preparing... ################################# [100%]
Updating / installing...
1:elrepo-release-8.2-1.el8.elrepo ################################# [100%]
Now, we can install the DRBD kernel module and utilities:
.. code-block:: none
# yum install -y kmod-drbd90 drbd90-utils
DRBD will not be able to run under the default SELinux security policies.
If you are familiar with SELinux, you can modify the policies in a more
fine-grained manner, but here we will simply exempt DRBD processes from SELinux
control:
.. code-block:: none
# yum install -y policycoreutils-python-utils
# semanage permissive -a drbd_t
We will configure DRBD to use port 7789, so allow that port from each host to
the other:
.. code-block:: none
[root@pcmk-1 ~]# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" \
source address="192.168.122.102" port port="7789" protocol="tcp" accept'
success
[root@pcmk-1 ~]# firewall-cmd --reload
success
.. code-block:: none
[root@pcmk-2 ~]# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" \
source address="192.168.122.101" port port="7789" protocol="tcp" accept'
success
[root@pcmk-2 ~]# firewall-cmd --reload
success
.. NOTE::
In this example, we have only two nodes, and all network traffic is on the same LAN.
In production, it is recommended to use a dedicated, isolated network for cluster-related traffic,
so the firewall configuration would likely be different; one approach would be to
add the dedicated network interfaces to the trusted zone.
.. NOTE::
If the ``firewall-cmd --add-rich-rule`` command fails with **Error:
INVALID_RULE: unknown element**, ensure that there is no space at the
beginning of the second line of the command.
Allocate a Disk Volume for DRBD
###############################
DRBD will need its own block device on each node. This can be
a physical disk partition or logical volume, of whatever size
you need for your data. For this document, we will use a 512MiB logical volume,
which is more than sufficient for a single HTML file and (later) GFS2 metadata.
.. code-block:: none
[root@pcmk-1 ~]# vgdisplay | grep -e Name -e Free
VG Name cs_pcmk-1
Free PE / Size 3583 / <14.00 GiB
[root@pcmk-1 ~]# lvcreate --name drbd-demo --size 512M cs_pcmk-1
Logical volume "drbd-demo" created.
[root@pcmk-1 ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
drbd-demo centos_pcmk-1 -wi-a----- 512.00m
root centos_pcmk-1 -wi-ao---- 3.00g
swap centos_pcmk-1 -wi-ao---- 1.00g
Repeat for the second node, making sure to use the same size:
.. code-block:: none
[root@pcmk-1 ~]# ssh pcmk-2 -- lvcreate --name drbd-demo --size 512M cs_pcmk-2
Logical volume "drbd-demo" created.
Configure DRBD
##############
There is no series of commands for building a DRBD configuration, so simply
run this on both nodes to use this sample configuration:
.. code-block:: none
# cat </etc/drbd.d/wwwdata.res
resource wwwdata {
protocol C;
meta-disk internal;
device /dev/drbd1;
syncer {
verify-alg sha1;
}
net {
allow-two-primaries;
}
on pcmk-1 {
disk /dev/cs_pcmk-1/drbd-demo;
address 192.168.122.101:7789;
}
on pcmk-2 {
disk /dev/cs_pcmk-2/drbd-demo;
address 192.168.122.102:7789;
}
}
END
.. IMPORTANT::
- Edit the file to use the hostnames, IP addresses and logical volume paths
+ Edit the file to use the hostnames, IP addresses, and logical volume paths
of your nodes if they differ from the ones used in this guide.
.. NOTE::
Detailed information on the directives used in this configuration (and
other alternatives) is available in the
`DRBD User's Guide
`_.
The **allow-two-primaries** option would not normally be used in
an active/passive cluster. We are adding it here for the convenience
of changing to an active/active cluster later.
Initialize DRBD
###############
With the configuration in place, we can now get DRBD running.
These commands create the local metadata for the DRBD resource,
ensure the DRBD kernel module is loaded, and bring up the DRBD resource.
Run them on one node:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm create-md wwwdata
initializing activity log
initializing bitmap (16 KB) to all zero
Writing meta data...
New drbd meta data block successfully created.
[root@pcmk-1 ~]# modprobe drbd
[root@pcmk-1 ~]# drbdadm up wwwdata
--== Thank you for participating in the global usage survey ==--
The server's response is:
you are the 801th user to install this version
- We can confirm DRBD's status on this node:
+We can confirm DRBD's status on this node:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm status
wwwdata role:Secondary
disk:Inconsistent
pcmk-2 connection:Connecting
Because we have not yet initialized the data, this node's data
is marked as **Inconsistent**. Because we have not yet initialized
the second node, the pcmk-2 connection is **Connecting** (waiting for connection).
Now, repeat the above commands on the second node, starting with creating
wwwdata.res. After giving it time to connect, when we check the status of the first
node, it shows:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm status
wwwdata role:Secondary
disk:Inconsistent
pcmk-2 role:Secondary
peer-disk:Inconsistent
You can see that **pcmk-2 connection:Connecting** longer appears in the
output, meaning the two DRBD nodes are communicating properly, and both
nodes are in **Secondary** role with **Inconsistent** data.
To make the data consistent, we need to tell DRBD which node should be
considered to have the correct data. In this case, since we are creating
a new resource, both have garbage, so we'll just pick pcmk-1
and run this command on it:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm primary --force wwwdata
.. NOTE::
If you are using a different version of DRBD, the required syntax may be different.
See the documentation for your version for how to perform these commands.
If we check the status of both nodes immediately, we'll see something like this:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm status
wwwdata role:Primary
disk:UpToDate
pcmk-1 role:Secondary
peer-disk:UpToDate
[root@pcmk-2 ~]# drbdadm status
wwwdata role:Secondary
disk:UpToDate
pcmk-1 role:Primary
peer-disk:Inconsistent
We can see that the first node has the **Primary** role, its partner node has
the **Secondary** role, the first node's data is now considered **UpToDate**,
the partner node's data is still **Inconsistent**.
After a while, the sync should finish, and you'll see something like:
.. code-block:: none
[root@pcmk-1 ~]# drbdadm status
wwwdata role:Primary
disk:UpToDate
pcmk-1 role:Secondary
peer-disk:UpToDate
[root@pcmk-2 ~]# drbdadm status
wwwdata role:Secondary
disk:UpToDate
pcmk-1 role:Primary
peer-disk:UpToDate
Both sets of data are now **UpToDate**, and we can proceed to creating
and populating a filesystem for our WebSite resource's documents.
Populate the DRBD Disk
######################
On the node with the primary role (pcmk-1 in this example),
create a filesystem on the DRBD device:
.. code-block:: none
[root@pcmk-1 ~]# mkfs.xfs /dev/drbd1
meta-data=/dev/drbd1 isize=512 agcount=4, agsize=32765 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=1
data = bsize=4096 blocks=131059, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=1368, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Discarding blocks...Done.
.. NOTE::
In this example, we create an xfs filesystem with no special options.
In a production environment, you should choose a filesystem type and
options that are suitable for your application.
Mount the newly created filesystem, populate it with our web document,
give it the same SELinux policy as the web document root,
then unmount it (the cluster will handle mounting and unmounting it later):
.. code-block:: none
[root@pcmk-1 ~]# mount /dev/drbd1 /mnt
[root@pcmk-1 ~]# cat <<-END >/mnt/index.html
My Test Site - DRBD
END
[root@pcmk-1 ~]# chcon -R --reference=/var/www/html /mnt
[root@pcmk-1 ~]# umount /dev/drbd1
Configure the Cluster for the DRBD device
#########################################
One handy feature ``pcs`` has is the ability to queue up several changes
into a file and commit those changes all at once. To do this, start by
populating the file with the current raw XML config from the CIB.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib drbd_cfg
Using pcs's ``-f`` option, make changes to the configuration saved
in the ``drbd_cfg`` file. These changes will not be seen by the cluster until
the ``drbd_cfg`` file is pushed into the live cluster's CIB later.
Here, we create a cluster resource for the DRBD device, and an additional *clone*
resource to allow the resource to run on both nodes at the same time.
.. code-block:: none
[root@pcmk-1 ~]# pcs -f drbd_cfg resource create WebData ocf:linbit:drbd \
drbd_resource=wwwdata op monitor interval=60s
[root@pcmk-1 ~]# pcs -f drbd_cfg resource promotable WebData \
promoted-max=1 promoted-node-max=1 clone-max=2 clone-node-max=1 \
notify=true
[root@pcmk-1 ~]# pcs resource status
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
[root@pcmk-1 ~]# pcs resource config
Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2)
Attributes: cidr_netmask=24 ip=192.168.122.120
Operations: monitor interval=30s (ClusterIP-monitor-interval-30s)
start interval=0s timeout=20s (ClusterIP-start-interval-0s)
stop interval=0s timeout=20s (ClusterIP-stop-interval-0s)
Resource: WebSite (class=ocf provider=heartbeat type=apache)
Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status
Operations: monitor interval=1min (WebSite-monitor-interval-1min)
start interval=0s timeout=40s (WebSite-start-interval-0s)
stop interval=0s timeout=60s (WebSite-stop-interval-0s)
After you are satisfied with all the changes, you can commit
them all at once by pushing the drbd_cfg file into the live CIB.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib-push drbd_cfg --config
CIB updated
Let's see what the cluster did with the new configuration:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Wed Feb 3 09:04:23 2021
* Last change: Wed Feb 3 09:04:18 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 4 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
We can see that **WebData-clone** (our DRBD device) is running as promoted
(DRBD's primary role) on **pcmk-1** and unpromoted (DRBD's secondary role) on
**pcmk-2**.
.. IMPORTANT::
The resource agent should load the DRBD module when needed if it's not already
loaded. If that does not happen, configure your operating system to load the
module at boot time. For |CFS_DISTRO| |CFS_DISTRO_VER|, you would run this on both
nodes:
.. code-block:: none
# echo drbd >/etc/modules-load.d/drbd.conf
Configure the Cluster for the Filesystem
########################################
Now that we have a working DRBD device, we need to mount its filesystem.
In addition to defining the filesystem, we also need to
tell the cluster where it can be located (only on the DRBD Primary)
and when it is allowed to start (after the Primary was promoted).
We are going to take a shortcut when creating the resource this time.
Instead of explicitly saying we want the **ocf:heartbeat:Filesystem** script, we
are only going to ask for **Filesystem**. We can do this because we know there is only
one resource script named **Filesystem** available to pacemaker, and that pcs is smart
enough to fill in the **ocf:heartbeat:** portion for us correctly in the configuration.
If there were multiple **Filesystem** scripts from different OCF providers, we would need
to specify the exact one we wanted.
Once again, we will queue our changes to a file and then push the
new configuration to the cluster as the final step.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib fs_cfg
[root@pcmk-1 ~]# pcs -f fs_cfg resource create WebFS Filesystem \
device="/dev/drbd1" directory="/var/www/html" fstype="xfs"
Assumed agent name 'ocf:heartbeat:Filesystem' (deduced from 'Filesystem')
[root@pcmk-1 ~]# pcs -f fs_cfg constraint colocation add \
WebFS with WebData-clone INFINITY with-rsc-role=Master
[root@pcmk-1 ~]# pcs -f fs_cfg constraint order \
promote WebData-clone then start WebFS
Adding WebData-clone WebFS (kind: Mandatory) (Options: first-action=promote then-action=start)
We also need to tell the cluster that Apache needs to run on the same
machine as the filesystem and that it must be active before Apache can
start.
.. code-block:: none
[root@pcmk-1 ~]# pcs -f fs_cfg constraint colocation add WebSite with WebFS INFINITY
[root@pcmk-1 ~]# pcs -f fs_cfg constraint order WebFS then WebSite
Adding WebFS WebSite (kind: Mandatory) (Options: first-action=start then-action=start)
Review the updated configuration.
.. code-block:: none
[root@pcmk-1 ~]# pcs -f fs_cfg constraint
Location Constraints:
Resource: WebSite
Enabled on:
Node: pcmk-1 (score:50)
Ordering Constraints:
start ClusterIP then start WebSite (kind:Mandatory)
promote WebData-clone then start WebFS (kind:Mandatory)
start WebFS then start WebSite (kind:Mandatory)
Colocation Constraints:
WebSite with ClusterIP (score:INFINITY)
WebFS with WebData-clone (score:INFINITY) (with-rsc-role:Master)
WebSite with WebFS (score:INFINITY)
Ticket Constraints:
[root@pcmk-1 ~]# pcs resource status
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
[root@pcmk-1 ~]# pcs resource config
Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2)
Attributes: cidr_netmask=24 ip=192.168.122.120
Operations: monitor interval=30s (ClusterIP-monitor-interval-30s)
start interval=0s timeout=20s (ClusterIP-start-interval-0s)
stop interval=0s timeout=20s (ClusterIP-stop-interval-0s)
Resource: WebSite (class=ocf provider=heartbeat type=apache)
Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status
Operations: monitor interval=1min (WebSite-monitor-interval-1min)
start interval=0s timeout=40s (WebSite-start-interval-0s)
stop interval=0s timeout=60s (WebSite-stop-interval-0s)
Clone: WebData-clone
Meta Attrs: clone-max=2 clone-node-max=1 notify=true promotable=true promoted-max=1 promoted-node-max=1
Resource: WebData (class=ocf provider=linbit type=drbd)
Attributes: drbd_resource=wwwdata
Operations: demote interval=0s timeout=90 (WebData-demote-interval-0s)
monitor interval=60s (WebData-monitor-interval-60s)
notify interval=0s timeout=90 (WebData-notify-interval-0s)
promote interval=0s timeout=90 (WebData-promote-interval-0s)
reload interval=0s timeout=30 (WebData-reload-interval-0s)
start interval=0s timeout=240 (WebData-start-interval-0s)
stop interval=0s timeout=100 (WebData-stop-interval-0s)
After reviewing the new configuration, upload it and watch the
cluster put it into effect.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib-push fs_cfg --config
CIB updated
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Wed Feb 3 09:17:24 2021
* Last change: Wed Feb 3 09:17:19 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 5 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
* WebFS (ocf::heartbeat:Filesystem): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Test Cluster Failover
#####################
Previously, we used ``pcs cluster stop pcmk-1`` to stop all cluster
services on **pcmk-1**, failing over the cluster resources, but there is another
way to safely simulate node failure.
We can put the node into *standby mode*. Nodes in this state continue to
run corosync and pacemaker but are not allowed to run resources. Any resources
found active there will be moved elsewhere. This feature can be particularly
useful when performing system administration tasks such as updating packages
used by cluster resources.
Put the active node into standby mode, and observe the cluster move all
the resources to the other node. The node's status will change to indicate that
it can no longer host resources, and eventually all the resources will move.
.. code-block:: none
[root@pcmk-1 ~]# pcs node standby pcmk-1
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Wed Feb 3 09:18:45 2021
* Last change: Wed Feb 3 09:18:35 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 5 resource instances configured
Node List:
* Node pcmk-1: standby
* Online: [ pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-2
* WebSite (ocf::heartbeat:apache): Started pcmk-2
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-2 ]
* Stopped: [ pcmk-1 ]
* WebFS (ocf::heartbeat:Filesystem): Started pcmk-2
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Once we've done everything we needed to on pcmk-1 (in this case nothing,
-we just wanted to see the resources move), we can allow the node to be a
-full cluster member again.
+we just wanted to see the resources move), we can unstandby the node, making it
+eligible to host resources again.
.. code-block:: none
[root@pcmk-1 ~]# pcs node unstandby pcmk-1
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Wed Feb 3 09:19:47 2021
* Last change: Wed Feb 3 09:19:29 2021 by root via cibadmin on pcmk-1
* 2 nodes configured
* 5 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* ClusterIP (ocf::heartbeat:IPaddr2): Started pcmk-1
* WebSite (ocf::heartbeat:apache): Started pcmk-1
* Clone Set: WebData-clone [WebData] (promotable):
* Masters: [ pcmk-1 ]
* Slaves: [ pcmk-2 ]
* WebFS (ocf::heartbeat:Filesystem): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Notice that **pcmk-1** is back to the **Online** state, and that the cluster resources
stay where they are due to our resource stickiness settings configured earlier.
.. [#] See http://www.drbd.org for details.
.. [#] Since version 2.6.33
diff --git a/doc/sphinx/Clusters_from_Scratch/verification.rst b/doc/sphinx/Clusters_from_Scratch/verification.rst
index b7fa20ea7e..af1438f290 100644
--- a/doc/sphinx/Clusters_from_Scratch/verification.rst
+++ b/doc/sphinx/Clusters_from_Scratch/verification.rst
@@ -1,215 +1,216 @@
Start and Verify Cluster
------------------------
Start the Cluster
#################
Now that corosync is configured, it is time to start the cluster.
The command below will start corosync and pacemaker on both nodes
in the cluster. If you are issuing the start command from a different
node than the one you ran the ``pcs host auth`` command on earlier, you
must authenticate on the current node you are logged into before you will
be allowed to start the cluster.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster start --all
pcmk-1: Starting Cluster...
pcmk-2: Starting Cluster...
.. NOTE::
An alternative to using the ``pcs cluster start --all`` command
is to issue either of the below command sequences on each node in the
cluster separately:
.. code-block:: none
# pcs cluster start
Starting Cluster...
or
.. code-block:: none
# systemctl start corosync.service
# systemctl start pacemaker.service
.. IMPORTANT::
In this example, we are not enabling the corosync and pacemaker services
- to start at boot. If a cluster node fails or is rebooted, you will need to run
- ``pcs cluster start `` (or ``--all``) to start the cluster on it.
- While you could enable the services to start at boot, requiring a manual start
- of cluster services gives you the opportunity to do a post-mortem investigation
- of a node failure before returning it to the cluster.
+ to start at boot. If a cluster node fails or is rebooted, you will need to
+ run ``pcs cluster start [ | --all]`` to start the cluster on it.
+ While you can enable the services to start at boot (for example, using
+ ``pcs cluster enable [ | --all]``), requiring a manual start of
+ cluster services gives you the opportunity to do a post-mortem
+ investigation of a node failure before returning it to the cluster.
Verify Corosync Installation
############################
First, use ``corosync-cfgtool`` to check whether cluster communication is happy:
.. code-block:: none
[root@pcmk-1 ~]# corosync-cfgtool -s
Printing link status.
Local node ID 1
LINK ID 0
addr = 192.168.122.101
status:
nodeid 1: localhost
nodeid 2: connected
We can see here that everything appears normal with our fixed IP
address (not a 127.0.0.x loopback address) listed as the **addr**, and **localhost** and **connected** for the statuses of nodeid 1 and nodeid 2, respectively.
If you see something different, you might want to start by checking
-the node's network, firewall and SELinux configurations.
+the node's network, firewall, and SELinux configurations.
Next, check the membership and quorum APIs:
.. code-block:: none
[root@pcmk-1 ~]# corosync-cmapctl | grep members
runtime.members.1.config_version (u64) = 0
runtime.members.1.ip (str) = r(0) ip(192.168.122.101)
runtime.members.1.join_count (u32) = 1
runtime.members.1.status (str) = joined
runtime.members.2.config_version (u64) = 0
runtime.members.2.ip (str) = r(0) ip(192.168.122.102)
runtime.members.2.join_count (u32) = 1
runtime.members.2.status (str) = joined
[root@pcmk-1 ~]# pcs status corosync
Membership information
----------------------
Nodeid Votes Name
1 1 pcmk-1 (local)
2 1 pcmk-2
You should see both nodes have joined the cluster.
Verify Pacemaker Installation
#############################
Now that we have confirmed that Corosync is functional, we can check
the rest of the stack. Pacemaker has already been started, so verify
the necessary processes are running:
.. code-block:: none
[root@pcmk-1 ~]# ps axf
PID TTY STAT TIME COMMAND
2 ? S 0:00 [kthreadd]
...lots of processes...
17121 ? SLsl 0:01 /usr/sbin/corosync -f
17133 ? Ss 0:00 /usr/sbin/pacemakerd
17134 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-based
17135 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-fenced
17136 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-execd
17137 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-attrd
17138 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-schedulerd
17139 ? Ss 0:00 \_ /usr/libexec/pacemaker/pacemaker-controld
If that looks OK, check the ``pcs status`` output:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
WARNINGS:
No stonith devices and stonith-enabled is not false
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
* Last updated: Wed Jan 20 07:54:02 2021
* Last change: Wed Jan 20 07:48:25 2021 by hacluster via crmd on pcmk-2
* 2 nodes configured
* 0 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* No resources
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Finally, ensure there are no start-up errors from corosync or pacemaker (aside
from messages relating to not having STONITH configured, which are OK at this
point):
.. code-block:: none
[root@pcmk-1 ~]# journalctl -b | grep -i error
.. NOTE::
- Other operating systems may report startup errors in other locations,
- for example ``/var/log/messages``.
+ Other operating systems may report startup errors in other locations
+ (for example, ``/var/log/messages``).
Repeat these checks on the other node. The results should be the same.
Explore the Existing Configuration
##################################
For those who are not of afraid of XML, you can see the raw cluster
configuration and status by using the ``pcs cluster cib`` command.
.. topic:: The last XML you'll see in this document
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib
.. code-block:: xml
Before we make any changes, it's a good idea to check the validity of
the configuration.
.. code-block:: none
[root@pcmk-1 ~]# crm_verify -L -V
error: unpack_resources: Resource start-up disabled since no STONITH resources have been defined
error: unpack_resources: Either configure some or disable STONITH with the stonith-enabled option
error: unpack_resources: NOTE: Clusters with shared data need STONITH to ensure data integrity
Errors found during check: config not valid
As you can see, the tool has found some errors. The cluster will not start any
resources until we configure STONITH.
diff --git a/doc/sphinx/shared/pacemaker-intro.rst b/doc/sphinx/shared/pacemaker-intro.rst
index 49ad93361b..e4473b05b9 100644
--- a/doc/sphinx/shared/pacemaker-intro.rst
+++ b/doc/sphinx/shared/pacemaker-intro.rst
@@ -1,196 +1,196 @@
What Is Pacemaker?
####################
Pacemaker is a high-availability *cluster resource manager* -- software that
runs on a set of hosts (a *cluster* of *nodes*) in order to preserve integrity
and minimize downtime of desired services (*resources*). [#]_ It is maintained
by the `ClusterLabs `_ community.
Pacemaker's key features include:
* Detection of and recovery from node- and service-level failures
* Ability to ensure data integrity by fencing faulty nodes
* Support for one or more nodes per cluster
* Support for multiple resource interface standards (anything that can be
scripted can be clustered)
* Support (but no requirement) for shared storage
* Support for practically any redundancy configuration (active/passive, N+1,
etc.)
* Automatically replicated configuration that can be updated from any node
* Ability to specify cluster-wide relationships between services,
- such as ordering, colocation and anti-colocation
+ such as ordering, colocation, and anti-colocation
* Support for advanced service types, such as *clones* (services that need to
be active on multiple nodes), *promotable clones* (clones that can run in
one of two roles), and containerized services
* Unified, scriptable cluster management tools
.. note:: **Fencing**
*Fencing*, also known as *STONITH* (an acronym for Shoot The Other Node In
The Head), is the ability to ensure that it is not possible for a node to be
running a service. This is accomplished via *fence devices* such as
intelligent power switches that cut power to the target, or intelligent
network switches that cut the target's access to the local network.
Pacemaker represents fence devices as a special class of resource.
A cluster cannot safely recover from certain failure conditions, such as an
unresponsive node, without fencing.
Cluster Architecture
____________________
At a high level, a cluster can be viewed as having these parts (which together
are often referred to as the *cluster stack*):
* **Resources:** These are the reason for the cluster's being -- the services
that need to be kept highly available.
* **Resource agents:** These are scripts or operating system components that
start, stop, and monitor resources, given a set of resource parameters.
These provide a uniform interface between Pacemaker and the managed
services.
* **Fence agents:** These are scripts that execute node fencing actions,
given a target and fence device parameters.
* **Cluster membership layer:** This component provides reliable messaging,
membership, and quorum information about the cluster. Currently, Pacemaker
supports `Corosync `_ as this layer.
* **Cluster resource manager:** Pacemaker provides the brain that processes
and reacts to events that occur in the cluster. These events may include
nodes joining or leaving the cluster; resource events caused by failures,
maintenance, or scheduled activities; and other administrative actions.
To achieve the desired availability, Pacemaker may start and stop resources
and fence nodes.
* **Cluster tools:** These provide an interface for users to interact with the
cluster. Various command-line and graphical (GUI) interfaces are available.
Most managed services are not, themselves, cluster-aware. However, many popular
open-source cluster filesystems make use of a common *Distributed Lock
Manager* (DLM), which makes direct use of Corosync for its messaging and
membership capabilities and Pacemaker for the ability to fence nodes.
.. image:: ../shared/images/pcmk-stack.png
:alt: Example cluster stack
:align: center
Pacemaker Architecture
______________________
Pacemaker itself is composed of multiple daemons that work together:
* pacemakerd
* pacemaker-attrd
* pacemaker-based
* pacemaker-controld
* pacemaker-execd
* pacemaker-fenced
* pacemaker-schedulerd
.. image:: ../shared/images/pcmk-internals.png
:alt: Pacemaker software components
:align: center
Pacemaker's main process (pacemakerd) spawns all the other daemons, and
respawns them if they unexpectedly exit.
The *Cluster Information Base* (CIB) is an
`XML `_ representation of the cluster's
configuration and the state of all nodes and resources. The *CIB manager*
(pacemaker-based) keeps the CIB synchronized across the cluster, and handles
requests to modify it.
The *attribute manager* (pacemaker-attrd) maintains a database of attributes
for all nodes, keeps it synchronized across the cluster, and handles requests
to modify them. These attributes are usually recorded in the CIB.
Given a snapshot of the CIB as input, the *scheduler* (pacemaker-schedulerd)
determines what actions are necessary to achieve the desired state of the
cluster.
The *local executor* (pacemaker-execd) handles requests to execute
resource agents on the local cluster node, and returns the result.
The *fencer* (pacemaker-fenced) handles requests to fence nodes. Given a target
node, the fencer decides which cluster node(s) should execute which fencing
device(s), and calls the necessary fencing agents (either directly, or via
requests to the fencer peers on other nodes), and returns the result.
The *controller* (pacemaker-controld) is Pacemaker's coordinator, maintaining a
consistent view of the cluster membership and orchestrating all the other
components.
Pacemaker centralizes cluster decision-making by electing one of the controller
instances as the *Designated Controller* (*DC*). Should the elected DC process
(or the node it is on) fail, a new one is quickly established. The DC responds
to cluster events by taking a current snapshot of the CIB, feeding it to the
scheduler, then asking the executors (either directly on the local node, or via
requests to controller peers on other nodes) and the fencer to execute any
necessary actions.
.. note:: **Old daemon names**
The Pacemaker daemons were renamed in version 2.0. You may still find
references to the old names, especially in documentation targeted to
version 1.1.
.. table::
+-------------------+---------------------+
| Old name | New name |
+===================+=====================+
| attrd | pacemaker-attrd |
+-------------------+---------------------+
| cib | pacemaker-based |
+-------------------+---------------------+
| crmd | pacemaker-controld |
+-------------------+---------------------+
| lrmd | pacemaker-execd |
+-------------------+---------------------+
| stonithd | pacemaker-fenced |
+-------------------+---------------------+
| pacemaker_remoted | pacemaker-remoted |
+-------------------+---------------------+
Node Redundancy Designs
_______________________
Pacemaker supports practically any `node redundancy configuration
`_
-including *Active/Active*, *Active/Passive*, *N+1*, *N+M*, *N-to-1* and
+including *Active/Active*, *Active/Passive*, *N+1*, *N+M*, *N-to-1*, and
*N-to-N*.
Active/passive clusters with two (or more) nodes using Pacemaker and
`DRBD `_ are
a cost-effective high-availability solution for many situations. One of the
nodes provides the desired services, and if it fails, the other node takes
over.
.. image:: ../shared/images/pcmk-active-passive.png
:alt: Active/Passive Redundancy
:align: center
Pacemaker also supports multiple nodes in a shared-failover design, reducing
hardware costs by allowing several active/passive clusters to be combined and
share a common backup node.
.. image:: ../shared/images/pcmk-shared-failover.png
:alt: Shared Failover
:align: center
When shared storage is available, every node can potentially be used for
failover. Pacemaker can even run multiple copies of services to spread out the
-workload. This is sometimes called N to N Redundancy.
+workload. This is sometimes called N-to-N redundancy.
.. image:: ../shared/images/pcmk-active-active.png
:alt: N to N Redundancy
:align: center
.. rubric:: Footnotes
.. [#] *Cluster* is sometimes used in other contexts to refer to hosts grouped
together for other purposes, such as high-performance computing (HPC),
but Pacemaker is not intended for those purposes.