diff --git a/doc/sphinx/Pacemaker_Explained/advanced-resources.rst b/doc/sphinx/Pacemaker_Explained/advanced-resources.rst
index 5d32685a3c..c63a1b0d45 100644
--- a/doc/sphinx/Pacemaker_Explained/advanced-resources.rst
+++ b/doc/sphinx/Pacemaker_Explained/advanced-resources.rst
@@ -1,1643 +1,1592 @@
Advanced Resource Types
-----------------------
.. index:
single: group resource
single: resource; group
.. _group-resources:
Groups - A Syntactic Shortcut
#############################
One of the most common elements of a cluster is a set of resources
that need to be located together, start sequentially, and stop in the
reverse order. To simplify this configuration, we support the concept
of groups.
.. topic:: A group of two primitive resources
.. code-block:: xml
<group id="shortcut">
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
<primitive id="Email" class="lsb" type="exim"/>
</group>
Although the example above contains only two resources, there is no
limit to the number of resources a group can contain. The example is
also sufficient to explain the fundamental properties of a group:
* Resources are started in the order they appear in (**Public-IP** first,
then **Email**)
* Resources are stopped in the reverse order to which they appear in
(**Email** first, then **Public-IP**)
If a resource in the group can't run anywhere, then nothing after that
is allowed to run, too.
* If **Public-IP** can't run anywhere, neither can **Email**;
* but if **Email** can't run anywhere, this does not affect **Public-IP**
in any way
The group above is logically equivalent to writing:
.. topic:: How the cluster sees a group resource
.. code-block:: xml
<configuration>
<resources>
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
<primitive id="Email" class="lsb" type="exim"/>
</resources>
<constraints>
<rsc_colocation id="xxx" rsc="Email" with-rsc="Public-IP" score="INFINITY"/>
<rsc_order id="yyy" first="Public-IP" then="Email"/>
</constraints>
</configuration>
Obviously as the group grows bigger, the reduced configuration effort
can become significant.
Another (typical) example of a group is a DRBD volume, the filesystem
mount, an IP address, and an application that uses them.
.. index::
pair: XML element; group
Group Properties
________________
.. table:: **Properties of a Group Resource**
+-------+--------------------------------------+
| Field | Description |
+=======+======================================+
| id | .. index:: |
| | single: group; property, id |
| | single: property; id (group) |
| | single: id; group property |
| | |
| | A unique name for the group |
+-------+--------------------------------------+
Group Options
_____________
Groups inherit the ``priority``, ``target-role``, and ``is-managed`` properties
from primitive resources. See :ref:`resource_options` for information about
those properties.
Group Instance Attributes
_________________________
Groups have no instance attributes. However, any that are set for the group
object will be inherited by the group's children.
Group Contents
______________
Groups may only contain a collection of cluster resources (see
:ref:`primitive-resource`). To refer to a child of a group resource, just use
the child's ``id`` instead of the group's.
Group Constraints
_________________
Although it is possible to reference a group's children in
constraints, it is usually preferable to reference the group itself.
.. topic:: Some constraints involving groups
.. code-block:: xml
<constraints>
<rsc_location id="group-prefers-node1" rsc="shortcut" node="node1" score="500"/>
<rsc_colocation id="webserver-with-group" rsc="Webserver" with-rsc="shortcut"/>
<rsc_order id="start-group-then-webserver" first="Webserver" then="shortcut"/>
</constraints>
.. index::
pair: resource-stickiness; group
Group Stickiness
________________
Stickiness, the measure of how much a resource wants to stay where it
is, is additive in groups. Every active resource of the group will
contribute its stickiness value to the group's total. So if the
default ``resource-stickiness`` is 100, and a group has seven members,
five of which are active, then the group as a whole will prefer its
current location with a score of 500.
.. index::
- single: clone resource
+ single: clone
single: resource; clone
.. _s-resource-clone:
Clones - Resources That Can Have Multiple Active Instances
##########################################################
*Clone* resources are resources that can have more than one copy active at the
same time. This allows you, for example, to run a copy of a daemon on every
node. You can clone any primitive or group resource [#]_.
Anonymous versus Unique Clones
______________________________
A clone resource is configured to be either *anonymous* or *globally unique*.
Anonymous clones are the simplest. These behave completely identically
everywhere they are running. Because of this, there can be only one instance of
an anonymous clone active per node.
The instances of globally unique clones are distinct entities. All instances
are launched identically, but one instance of the clone is not identical to any
other instance, whether running on the same node or a different node. As an
example, a cloned IP address can use special kernel functionality such that
each instance handles a subset of requests for the same IP address.
.. index::
- single: Promotable Clone Resources
+ single: promotable clone
single: resource; promotable
.. _s-resource-promotable:
Promotable clones
_________________
If a clone is *promotable*, its instances can perform a special role that
Pacemaker will manage via the ``promote`` and ``demote`` actions of the resource
agent.
Services that support such a special role have various terms for the special
role and the default role: primary and secondary, master and replica,
controller and worker, etc. Pacemaker uses the terms *master* and *slave* [#]_,
but is agnostic to what the service calls them or what they do.
All that Pacemaker cares about is that an instance comes up in the default role
when started, and the resource agent supports the ``promote`` and ``demote`` actions
to manage entering and exiting the special role.
.. index::
pair: XML element; clone
Clone Properties
________________
.. table:: **Properties of a Clone Resource**
+-------+--------------------------------------+
| Field | Description |
+=======+======================================+
| id | .. index:: |
| | single: clone; property, id |
| | single: property; id (clone) |
| | single: id; clone property |
| | |
| | A unique name for the clone |
+-------+--------------------------------------+
.. index::
pair: options; clone
Clone Options
_____________
:ref:`Options <resource_options>` inherited from primitive resources:
``priority, target-role, is-managed``
.. table:: **Clone-specific configuration options**
+-------------------+-----------------+-------------------------------------------------------+
| Field | Default | Description |
+===================+=================+=======================================================+
| globally-unique | false | .. index:: |
| | | single: clone; option, globally-unique |
| | | single: option; globally-unique (clone) |
| | | single: globally-unique; clone option |
| | | |
| | | If **true**, each clone instance performs a |
| | | distinct function |
+-------------------+-----------------+-------------------------------------------------------+
| clone-max | number of nodes | .. index:: |
| | in the cluster | single: clone; option, clone-max |
| | | single: option; clone-max (clone) |
| | | single: clone-max; clone option |
| | | |
| | | The maximum number of clone instances that can |
| | | be started across the entire cluster |
+-------------------+-----------------+-------------------------------------------------------+
| clone-node-max | 1 | .. index:: |
| | | single: clone; option, clone-node-max |
| | | single: option; clone-node-max (clone) |
| | | single: clone-node-max; clone option |
| | | |
| | | If ``globally-unique`` is **true**, the maximum |
| | | number of clone instances that can be started |
| | | on a single node |
+-------------------+-----------------+-------------------------------------------------------+
| clone-min | 0 | .. index:: |
| | | single: clone; option, clone-min |
| | | single: option; clone-min (clone) |
| | | single: clone-min; clone option |
| | | |
| | | Require at least this number of clone instances |
| | | to be runnable before allowing resources |
| | | depending on the clone to be runnable. A value |
| | | of 0 means require all clone instances to be |
| | | runnable. |
+-------------------+-----------------+-------------------------------------------------------+
| notify | false | .. index:: |
| | | single: clone; option, notify |
| | | single: option; notify (clone) |
| | | single: notify; clone option |
| | | |
| | | Call the resource agent's **notify** action for |
| | | all active instances, before and after starting |
| | | or stopping any clone instance. The resource |
| | | agent must support this action. |
| | | Allowed values: **false**, **true** |
+-------------------+-----------------+-------------------------------------------------------+
| ordered | false | .. index:: |
| | | single: clone; option, ordered |
| | | single: option; ordered (clone) |
| | | single: ordered; clone option |
| | | |
| | | If **true**, clone instances must be started |
| | | sequentially instead of in parallel. |
| | | Allowed values: **false**, **true** |
+-------------------+-----------------+-------------------------------------------------------+
| interleave | false | .. index:: |
| | | single: clone; option, interleave |
| | | single: option; interleave (clone) |
| | | single: interleave; clone option |
| | | |
| | | When this clone is ordered relative to another |
| | | clone, if this option is **false** (the default), |
| | | the ordering is relative to *all* instances of |
| | | the other clone, whereas if this option is |
| | | **true**, the ordering is relative only to |
| | | instances on the same node. |
| | | Allowed values: **false**, **true** |
+-------------------+-----------------+-------------------------------------------------------+
| promotable | false | .. index:: |
| | | single: clone; option, promotable |
| | | single: option; promotable (clone) |
| | | single: promotable; clone option |
| | | |
| | | If **true**, clone instances can perform a |
| | | special role that Pacemaker will manage via the |
| | | resource agent's **promote** and **demote** |
| | | actions. The resource agent must support these |
| | | actions. |
| | | Allowed values: **false**, **true** |
+-------------------+-----------------+-------------------------------------------------------+
| promoted-max | 1 | .. index:: |
| | | single: clone; option, promoted-max |
| | | single: option; promoted-max (clone) |
| | | single: promoted-max; clone option |
| | | |
| | | If ``promotable`` is **true**, the number of |
| | | instances that can be promoted at one time |
| | | across the entire cluster |
+-------------------+-----------------+-------------------------------------------------------+
| promoted-node-max | 1 | .. index:: |
| | | single: clone; option, promoted-node-max |
| | | single: option; promoted-node-max (clone) |
| | | single: promoted-node-max; clone option |
| | | |
| | | If ``promotable`` is **true** and ``globally-unique`` |
| | | is **false**, the number of clone instances can be |
| | | promoted at one time on a single node |
+-------------------+-----------------+-------------------------------------------------------+
For backward compatibility, ``master-max`` and ``master-node-max`` are accepted as
aliases for ``promoted-max`` and ``promoted-node-max``, but are deprecated since
2.0.0, and support for them will be removed in a future version.
Clone Contents
______________
Clones must contain exactly one primitive or group resource.
.. topic:: A clone that runs a web server on all nodes
.. code-block:: xml
<clone id="apache-clone">
<primitive id="apache" class="lsb" type="apache">
<operations>
<op id="apache-monitor" name="monitor" interval="30"/>
</operations>
</primitive>
</clone>
.. warning::
You should never reference the name of a clone's child (the primitive or group
resource being cloned). If you think you need to do this, you probably need to
re-evaluate your design.
Clone Instance Attribute
________________________
Clones have no instance attributes; however, any that are set here will be
inherited by the clone's child.
+.. index::
+ single: clone; constraint
+
Clone Constraints
_________________
In most cases, a clone will have a single instance on each active cluster
node. If this is not the case, you can indicate which nodes the
cluster should preferentially assign copies to with resource location
constraints. These constraints are written no differently from those
for primitive resources except that the clone's **id** is used.
.. topic:: Some constraints involving clones
.. code-block:: xml
<constraints>
<rsc_location id="clone-prefers-node1" rsc="apache-clone" node="node1" score="500"/>
<rsc_colocation id="stats-with-clone" rsc="apache-stats" with="apache-clone"/>
<rsc_order id="start-clone-then-stats" first="apache-clone" then="apache-stats"/>
</constraints>
Ordering constraints behave slightly differently for clones. In the
example above, ``apache-stats`` will wait until all copies of ``apache-clone``
that need to be started have done so before being started itself.
Only if *no* copies can be started will ``apache-stats`` be prevented
from being active. Additionally, the clone will wait for
``apache-stats`` to be stopped before stopping itself.
Colocation of a primitive or group resource with a clone means that
the resource can run on any node with an active instance of the clone.
The cluster will choose an instance based on where the clone is running and
the resource's own location preferences.
Colocation between clones is also possible. If one clone **A** is colocated
with another clone **B**, the set of allowed locations for **A** is limited to
nodes on which **B** is (or will be) active. Placement is then performed
normally.
+.. index::
+ single: promotable clone; constraint
+
+.. _promotable-clone-constraints:
+
Promotable Clone Constraints
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For promotable clone resources, the ``first-action`` and/or ``then-action`` fields
for ordering constraints may be set to ``promote`` or ``demote`` to constrain the
master role, and colocation constraints may contain ``rsc-role`` and/or
``with-rsc-role`` fields.
-.. index::
- single: constraint; colocation
-
-.. table:: **Additional colocation constraint options for promotable clone resources**
-
- +---------------+---------+-------------------------------------------------------+
- | Field | Default | Description |
- +===============+=========+=======================================================+
- | rsc-role | Started | .. index:: |
- | | | single: clone; ordering constraint, rsc-role |
- | | | single: ordering constraint; rsc-role (clone) |
- | | | single: rsc-role; clone ordering constraint |
- | | | |
- | | | An additional attribute of colocation constraints |
- | | | that specifies the role that ``rsc`` must be in. |
- | | | Allowed values: **Started**, **Master**, **Slave**. |
- +---------------+---------+-------------------------------------------------------+
- | with-rsc-role | Started | .. index:: |
- | | | single: clone; ordering constraint, with-rsc-role |
- | | | single: ordering constraint; with-rsc-role (clone) |
- | | | single: with-rsc-role; clone ordering constraint |
- | | | |
- | | | An additional attribute of colocation constraints |
- | | | that specifies the role that ``with-rsc`` must be in. |
- | | | Allowed values: **Started**, **Master**, **Slave**. |
- +---------------+---------+-------------------------------------------------------+
-
.. topic:: Constraints involving promotable clone resources
.. code-block:: xml
<constraints>
<rsc_location id="db-prefers-node1" rsc="database" node="node1" score="500"/>
<rsc_colocation id="backup-with-db-slave" rsc="backup"
with-rsc="database" with-rsc-role="Slave"/>
<rsc_colocation id="myapp-with-db-master" rsc="myApp"
with-rsc="database" with-rsc-role="Master"/>
<rsc_order id="start-db-before-backup" first="database" then="backup"/>
<rsc_order id="promote-db-then-app" first="database" first-action="promote"
then="myApp" then-action="start"/>
</constraints>
In the example above, **myApp** will wait until one of the database
copies has been started and promoted to master before being started
itself on the same node. Only if no copies can be promoted will **myApp** be
prevented from being active. Additionally, the cluster will wait for
**myApp** to be stopped before demoting the database.
Colocation of a primitive or group resource with a promotable clone
resource means that it can run on any node with an active instance of
the promotable clone resource that has the specified role (**master** or
**slave**). In the example above, the cluster will choose a location based on
where database is running as a **master**, and if there are multiple
**master** instances it will also factor in **myApp**'s own location
preferences when deciding which location to choose.
Colocation with regular clones and other promotable clone resources is also
possible. In such cases, the set of allowed locations for the **rsc**
clone is (after role filtering) limited to nodes on which the
``with-rsc`` promotable clone resource is (or will be) in the specified role.
Placement is then performed as normal.
Using Promotable Clone Resources in Colocation Sets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. index::
- single: constraint; colocation
- single: constraint; resource set
-
-.. table:: **Additional colocation set options relevant to promotable clone resources**
-
- +-------+---------+-----------------------------------------------------+
- | Field | Default | Description |
- +=======+=========+=====================================================+
- | role | Started | .. index:: |
- | | | single: clone; ordering constraint; role |
- | | | single: ordering constraint; role (clone) |
- | | | single: role; clone ordering constraint |
- | | | |
- | | | The role that *all members* of the set must be in. |
- | | | Allowed values: **Started**, **Master**, **Slave**. |
- +-------+---------+-----------------------------------------------------+
+When a promotable clone is used in a :ref:`resource set <s-resource-sets>`
+inside a colocation constraint, the resource set may take a ``role`` attribute.
In the following example **B**'s master must be located on the same node as **A**'s master.
Additionally resources **C** and **D** must be located on the same node as **A**'s
and **B**'s masters.
.. topic:: Colocate C and D with A's and B's master instances
.. code-block:: xml
<constraints>
<rsc_colocation id="coloc-1" score="INFINITY" >
<resource_set id="colocated-set-example-1" sequential="true" role="Master">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
<resource_set id="colocated-set-example-2" sequential="true">
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
</rsc_colocation>
</constraints>
Using Promotable Clone Resources in Ordered Sets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. index::
- single: constraint; colocation
- single: constraint; resource set
-
-.. table:: **Additional ordered set options relevant to promotable clone resources**
-
- +--------+------------------+-----------------------------------------------------+
- | Field | Default | Description |
- +=======++==================+=====================================================+
- | action | value of | .. index:: |
- | | ``first-action`` | single: clone; ordering constraint; action |
- | | | single: ordering constraintl action (clone) |
- | | | single: action; clone ordering constraint |
- | | | |
- | | | An additional attribute of ordering constraint |
- | | | sets that specifies the action that applies to |
- | | | *all members* of the set. |
- | | | Allowed values: **start**, **stop**, **promote**, |
- | | | **demote**. |
- +--------+------------------+-----------------------------------------------------+
-
+When a promotable clone is used in a :ref:`resource set <s-resource-sets>`
+inside an ordering constraint, the resource set may take an ``action``
+attribute.
+
.. topic:: Start C and D after first promoting A and B
.. code-block:: xml
<constraints>
<rsc_order id="order-1" score="INFINITY" >
<resource_set id="ordered-set-1" sequential="true" action="promote">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
<resource_set id="ordered-set-2" sequential="true" action="start">
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
</rsc_order>
</constraints>
In the above example, **B** cannot be promoted to a master role until **A** has
been promoted. Additionally, resources **C** and **D** must wait until **A** and **B**
have been promoted before they can start.
.. index::
pair: resource-stickiness; clone
.. _s-clone-stickiness:
Clone Stickiness
________________
To achieve a stable allocation pattern, clones are slightly sticky by
default. If no value for ``resource-stickiness`` is provided, the clone
will use a value of 1. Being a small value, it causes minimal
disturbance to the score calculations of other resources but is enough
to prevent Pacemaker from needlessly moving copies around the cluster.
.. note::
For globally unique clones, this may result in multiple instances of the
clone staying on a single node, even after another eligible node becomes
active (for example, after being put into standby mode then made active again).
If you do not want this behavior, specify a ``resource-stickiness`` of 0
for the clone temporarily and let the cluster adjust, then set it back
to 1 if you want the default behavior to apply again.
.. important::
If ``resource-stickiness`` is set in the ``rsc_defaults`` section, it will
apply to clone instances as well. This means an explicit ``resource-stickiness``
of 0 in ``rsc_defaults`` works differently from the implicit default used when
``resource-stickiness`` is not specified.
Clone Resource Agent Requirements
_________________________________
Any resource can be used as an anonymous clone, as it requires no
additional support from the resource agent. Whether it makes sense to
do so depends on your resource and its resource agent.
Resource Agent Requirements for Globally Unique Clones
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Globally unique clones require additional support in the resource agent. In
particular, it must only respond with ``${OCF_SUCCESS}`` if the node has that
exact instance active. All other probes for instances of the clone should
result in ``${OCF_NOT_RUNNING}`` (or one of the other OCF error codes if
they are failed).
Individual instances of a clone are identified by appending a colon and a
numerical offset, e.g. **apache:2**.
Resource agents can find out how many copies there are by examining
the ``OCF_RESKEY_CRM_meta_clone_max`` environment variable and which
instance it is by examining ``OCF_RESKEY_CRM_meta_clone``.
The resource agent must not make any assumptions (based on
``OCF_RESKEY_CRM_meta_clone``) about which numerical instances are active. In
particular, the list of active copies will not always be an unbroken
sequence, nor always start at 0.
Resource Agent Requirements for Promotable Clones
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Promotable clone resources require two extra actions, ``demote`` and ``promote``,
which are responsible for changing the state of the resource. Like **start** and
**stop**, they should return ``${OCF_SUCCESS}`` if they completed successfully or
a relevant error code if they did not.
The states can mean whatever you wish, but when the resource is
started, it must come up in the mode called **slave**. From there the
cluster will decide which instances to promote to **master**.
In addition to the clone requirements for monitor actions, agents must
also *accurately* report which state they are in. The cluster relies
on the agent to report its status (including role) accurately and does
not indicate to the agent what role it currently believes it to be in.
.. table:: **Role implications of OCF return codes**
+---------------------+------------------------------------------------+
| Monitor Return Code | Description |
+=====================+================================================+
| OCF_NOT_RUNNING | .. index:: |
| | single: OCF_NOT_RUNNING |
| | single: OCF return code; OCF_NOT_RUNNING |
| | |
| | Stopped |
+---------------------+------------------------------------------------+
| OCF_SUCCESS | .. index:: |
| | single: OCF_SUCCESS |
| | single: OCF return code; OCF_SUCCESS |
| | |
| | Running (Slave) |
+---------------------+------------------------------------------------+
| OCF_RUNNING_MASTER | .. index:: |
| | single: OCF_RUNNING_MASTER |
| | single: OCF return code; OCF_RUNNING_MASTER |
| | |
| | Running (Master) |
+---------------------+------------------------------------------------+
| OCF_FAILED_MASTER | .. index:: |
| | single: OCF_FAILED_MASTER |
| | single: OCF return code; OCF_FAILED_MASTER |
| | |
| | Failed (Master) |
+---------------------+------------------------------------------------+
| Other | .. index:: |
| | single: return code |
| | |
| | Failed (Slave) |
+---------------------+------------------------------------------------+
Clone Notifications
~~~~~~~~~~~~~~~~~~~
If the clone has the ``notify`` meta-attribute set to **true**, and the resource
agent supports the ``notify`` action, Pacemaker will call the action when
appropriate, passing a number of extra variables which, when combined with
additional context, can be used to calculate the current state of the cluster
and what is about to happen to it.
.. index::
single: clone; environment variables
single: notify; environment variables
.. table:: **Environment variables supplied with Clone notify actions**
+----------------------------------------------+-------------------------------------------------------------------------------+
| Variable | Description |
+==============================================+===============================================================================+
| OCF_RESKEY_CRM_meta_notify_type | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_type |
| | single: OCF_RESKEY_CRM_meta_notify_type |
| | |
| | Allowed values: **pre**, **post** |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_operation | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_operation |
| | single: OCF_RESKEY_CRM_meta_notify_operation |
| | |
| | Allowed values: **start**, **stop** |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_start_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_start_resource |
| | single: OCF_RESKEY_CRM_meta_notify_start_resource |
| | |
| | Resources to be started |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_stop_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_stop_resource |
| | single: OCF_RESKEY_CRM_meta_notify_stop_resource |
| | |
| | Resources to be stopped |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_active_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_active_resource |
| | single: OCF_RESKEY_CRM_meta_notify_active_resource |
| | |
| | Resources that are running |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_inactive_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_inactive_resource |
| | single: OCF_RESKEY_CRM_meta_notify_inactive_resource |
| | |
| | Resources that are not running |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_start_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_start_uname |
| | single: OCF_RESKEY_CRM_meta_notify_start_uname |
| | |
| | Nodes on which resources will be started |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_stop_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_stop_uname |
| | single: OCF_RESKEY_CRM_meta_notify_stop_uname |
| | |
| | Nodes on which resources will be stopped |
+----------------------------------------------+-------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_active_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_active_uname |
| | single: OCF_RESKEY_CRM_meta_notify_active_uname |
| | |
| | Nodes on which resources are running |
+----------------------------------------------+-------------------------------------------------------------------------------+
The variables come in pairs, such as
``OCF_RESKEY_CRM_meta_notify_start_resource`` and
``OCF_RESKEY_CRM_meta_notify_start_uname``, and should be treated as an
array of whitespace-separated elements.
``OCF_RESKEY_CRM_meta_notify_inactive_resource`` is an exception, as the
matching **uname** variable does not exist since inactive resources
are not running on any node.
Thus, in order to indicate that **clone:0** will be started on **sles-1**,
**clone:2** will be started on **sles-3**, and **clone:3** will be started
on **sles-2**, the cluster would set:
.. topic:: Notification variables
.. code-block:: none
OCF_RESKEY_CRM_meta_notify_start_resource="clone:0 clone:2 clone:3"
OCF_RESKEY_CRM_meta_notify_start_uname="sles-1 sles-3 sles-2"
.. note::
Pacemaker will log but otherwise ignore failures of notify actions.
Interpretation of Notification Variables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
**Pre-notification (stop):**
* Active resources: ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* Inactive resources: ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
**Post-notification (stop) / Pre-notification (start):**
* Active resources
* ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Inactive resources
* ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources that were started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources that were stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
**Post-notification (start):**
* Active resources:
* ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Inactive resources:
* ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources that were started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources that were stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
Extra Notifications for Promotable Clones
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. index::
single: clone; environment variables
single: promotable; environment variables
.. table:: **Extra environment variables supplied for promotable clones**
+---------------------------------------------+------------------------------------------------------------------------------+
| Variable | Description |
+=============================================+==============================================================================+
| OCF_RESKEY_CRM_meta_notify_master_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_master_resource |
| | single: OCF_RESKEY_CRM_meta_notify_master_resource |
| | |
| | Resources that are running in **Master** mode |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_slave_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_slave_resource |
| | single: OCF_RESKEY_CRM_meta_notify_slave_resource |
| | |
| | Resources that are running in **Slave** mode |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_promote_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_promote_resource |
| | single: OCF_RESKEY_CRM_meta_notify_promote_resource |
| | |
| | Resources to be promoted |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_demote_resource | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_demote_resource |
| | single: OCF_RESKEY_CRM_meta_notify_demote_resource |
| | |
| | Resources to be demoted |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_promote_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_promote_uname |
| | single: OCF_RESKEY_CRM_meta_notify_promote_uname |
| | |
| | Nodes on which resources will be promoted |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_demote_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_demote_uname |
| | single: OCF_RESKEY_CRM_meta_notify_demote_uname |
| | |
| | Nodes on which resources will be demoted |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_master_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_master_uname |
| | single: OCF_RESKEY_CRM_meta_notify_master_uname |
| | |
| | Nodes on which resources are running in **Master** mode |
+---------------------------------------------+------------------------------------------------------------------------------+
| OCF_RESKEY_CRM_meta_notify_slave_uname | .. index:: |
| | single: environment variable; OCF_RESKEY_CRM_meta_notify_slave_uname |
| | single: OCF_RESKEY_CRM_meta_notify_slave_uname |
| | |
| | Nodes on which resources are running in **Slave** mode |
+---------------------------------------------+------------------------------------------------------------------------------+
Interpretation of Promotable Notification Variables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
**Pre-notification (demote):**
* **Active** resources: ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* **Master** resources: ``$OCF_RESKEY_CRM_meta_notify_master_resource``
* **Slave** resources: ``$OCF_RESKEY_CRM_meta_notify_slave_resource``
* Inactive resources: ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources to be demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
**Post-notification (demote) / Pre-notification (stop):**
* **Active** resources: ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* **Master** resources:
* ``$OCF_RESKEY_CRM_meta_notify_master_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* **Slave** resources: ``$OCF_RESKEY_CRM_meta_notify_slave_resource``
* Inactive resources: ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources to be demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources that were demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
**Post-notification (stop) / Pre-notification (start)**
* **Active** resources:
* ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* **Master** resources:
* ``$OCF_RESKEY_CRM_meta_notify_master_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* **Slave** resources:
* ``$OCF_RESKEY_CRM_meta_notify_slave_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Inactive resources:
* ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources to be demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources that were demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources that were stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
**Post-notification (start) / Pre-notification (promote)**
* **Active** resources:
* ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* **Master** resources:
* ``$OCF_RESKEY_CRM_meta_notify_master_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* **Slave** resources:
* ``$OCF_RESKEY_CRM_meta_notify_slave_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Inactive resources:
* ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources to be demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources that were started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources that were demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources that were stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
**Post-notification (promote)**
* **Active** resources:
* ``$OCF_RESKEY_CRM_meta_notify_active_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* **Master** resources:
* ``$OCF_RESKEY_CRM_meta_notify_master_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* **Slave** resources:
* ``$OCF_RESKEY_CRM_meta_notify_slave_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Inactive resources:
* ``$OCF_RESKEY_CRM_meta_notify_inactive_resource``
* plus ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* minus ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources to be promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources to be demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources to be stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
* Resources that were started: ``$OCF_RESKEY_CRM_meta_notify_start_resource``
* Resources that were promoted: ``$OCF_RESKEY_CRM_meta_notify_promote_resource``
* Resources that were demoted: ``$OCF_RESKEY_CRM_meta_notify_demote_resource``
* Resources that were stopped: ``$OCF_RESKEY_CRM_meta_notify_stop_resource``
Monitoring Promotable Clone Resources
_____________________________________
The usual monitor actions are insufficient to monitor a promotable clone
resource, because Pacemaker needs to verify not only that the resource is
active, but also that its actual role matches its intended one.
Define two monitoring actions: the usual one will cover the slave role,
and an additional one with ``role="master"`` will cover the master role.
.. topic:: Monitoring both states of a promotable clone resource
.. code-block:: xml
<clone id="myMasterRsc">
<meta_attributes id="myMasterRsc-meta">
<nvpair name="promotable" value="true"/>
</meta_attributes>
<primitive id="myRsc" class="ocf" type="myApp" provider="myCorp">
<operations>
<op id="public-ip-slave-check" name="monitor" interval="60"/>
<op id="public-ip-master-check" name="monitor" interval="61" role="Master"/>
</operations>
</primitive>
</clone>
.. important::
It is crucial that *every* monitor operation has a different interval!
Pacemaker currently differentiates between operations
only by resource and interval; so if (for example) a promotable clone resource
had the same monitor interval for both roles, Pacemaker would ignore the
role when checking the status -- which would cause unexpected return
codes, and therefore unnecessary complications.
.. _s-promotion-scores:
Determining Which Instance is Promoted
______________________________________
Pacemaker can choose a promotable clone instance to be promoted in one of two
ways:
* Promotion scores: These are node attributes set via the ``crm_master`` utility,
which generally would be called by the resource agent's start action if it
supports promotable clones. This tool automatically detects both the resource
and host, and should be used to set a preference for being promoted. Based on
this, ``promoted-max``, and ``promoted-node-max``, the instance(s) with the
highest preference will be promoted.
* Constraints: Location constraints can indicate which nodes are most preferred
as masters.
.. topic:: Explicitly preferring node1 to be promoted to master
.. code-block:: xml
<rsc_location id="master-location" rsc="myMasterRsc">
<rule id="master-rule" score="100" role="Master">
<expression id="master-exp" attribute="#uname" operation="eq" value="node1"/>
</rule>
</rsc_location>
.. index:
single: bundle resource
single: resource; bundle
pair: container; Docker
pair: container; podman
pair: container; rkt
.. _s-resource-bundle:
Bundles - Isolated Environments
###############################
Pacemaker supports a special syntax for launching a
`container <https://en.wikipedia.org/wiki/Operating-system-level_virtualization>`_
with any infrastructure it requires: the *bundle*.
Pacemaker bundles support `Docker <https://www.docker.com/>`_,
`podman <https://podman.io/>`_ *(since 2.0.1)*, and
`rkt <https://coreos.com/rkt/>`_ container technologies. [#]_
.. topic:: A bundle for a containerized web server
.. code-block:: xml
<bundle id="httpd-bundle">
<podman image="pcmk:http" replicas="3"/>
<network ip-range-start="192.168.122.131"
host-netmask="24"
host-interface="eth0">
<port-mapping id="httpd-port" port="80"/>
</network>
<storage>
<storage-mapping id="httpd-syslog"
source-dir="/dev/log"
target-dir="/dev/log"
options="rw"/>
<storage-mapping id="httpd-root"
source-dir="/srv/html"
target-dir="/var/www/html"
options="rw,Z"/>
<storage-mapping id="httpd-logs"
source-dir-root="/var/log/pacemaker/bundles"
target-dir="/etc/httpd/logs"
options="rw,Z"/>
</storage>
<primitive class="ocf" id="httpd" provider="heartbeat" type="apache"/>
</bundle>
.. index:
single: bundle resource
single: resource; bundle
Bundle Prerequisites
____________________
Before configuring a bundle in Pacemaker, the user must install the appropriate
container launch technology (Docker, podman, or rkt), and supply a fully
configured container image, on every node allowed to run the bundle.
Pacemaker will create an implicit resource of type **ocf:heartbeat:docker**,
**ocf:heartbeat:podman**, or **ocf:heartbeat:rkt** to manage a bundle's
container. The user must ensure that the appropriate resource agent is
installed on every node allowed to run the bundle.
.. index::
pair: XML element; bundle
Bundle Properties
_________________
.. table:: **XML Attributes of a bundle Element**
+-------------+-----------------------------------------------+
| Attribute | Description |
+=============+===============================================+
| id | .. index:: |
| | single: bundle; attribute, id |
| | single: attribute; id (bundle) |
| | single: id; bundle attribute |
| | |
| | A unique name for the bundle (required) |
+-------------+-----------------------------------------------+
| description | .. index:: |
| | single: bundle; attribute, description |
| | single: attribute; description (bundle) |
| | single: description; bundle attribute |
| | |
| | Arbitrary text (not used by Pacemaker) |
+-------------+-----------------------------------------------+
A bundle must contain exactly one ``docker``, ``podman``, or ``rkt`` element.
.. index::
pair: XML element; docker
pair: XML element; podman
pair: XML element; rkt
single: resource; bundle
Bundle Container Properties
___________________________
.. table:: **XML attributes of a docker, podman, or rkt Element**
+-------------------+------------------------------------+---------------------------------------------------+
| Attribute | Default | Description |
+===================+====================================+===================================================+
| image | | .. index:: |
| | | single: docker; attribute, image |
| | | single: attribute; image (docker) |
| | | single: image; docker attribute |
| | | single: podman; attribute, image |
| | | single: attribute; image (podman) |
| | | single: image; podman attribute |
| | | single: rkt; attribute, image |
| | | single: attribute; image (rkt) |
| | | single: image; rkt attribute |
| | | |
| | | Container image tag (required) |
+-------------------+------------------------------------+---------------------------------------------------+
| replicas | Value of ``promoted-max`` | .. index:: |
| | if that is positive, else 1 | single: docker; attribute, replicas |
| | | single: attribute; replicas (docker) |
| | | single: replicas; docker attribute |
| | | single: podman; attribute, replicas |
| | | single: attribute; replicas (podman) |
| | | single: replicas; podman attribute |
| | | single: rkt; attribute, replicas |
| | | single: attribute; replicas (rkt) |
| | | single: replicas; rkt attribute |
| | | |
| | | A positive integer specifying the number of |
| | | container instances to launch |
+-------------------+------------------------------------+---------------------------------------------------+
| replicas-per-host | 1 | .. index:: |
| | | single: docker; attribute, replicas-per-host |
| | | single: attribute; replicas-per-host (docker) |
| | | single: replicas-per-host; docker attribute |
| | | single: podman; attribute, replicas-per-host |
| | | single: attribute; replicas-per-host (podman) |
| | | single: replicas-per-host; podman attribute |
| | | single: rkt; attribute, replicas-per-host |
| | | single: attribute; replicas-per-host (rkt) |
| | | single: replicas-per-host; rkt attribute |
| | | |
| | | A positive integer specifying the number of |
| | | container instances allowed to run on a |
| | | single node |
+-------------------+------------------------------------+---------------------------------------------------+
| promoted-max | 0 | .. index:: |
| | | single: docker; attribute, promoted-max |
| | | single: attribute; promoted-max (docker) |
| | | single: promoted-max; docker attribute |
| | | single: podman; attribute, promoted-max |
| | | single: attribute; promoted-max (podman) |
| | | single: promoted-max; podman attribute |
| | | single: rkt; attribute, promoted-max |
| | | single: attribute; promoted-max (rkt) |
| | | single: promoted-max; rkt attribute |
| | | |
| | | A non-negative integer that, if positive, |
| | | indicates that the containerized service |
| | | should be treated as a promotable service, |
| | | with this many replicas allowed to run the |
| | | service in the master role |
+-------------------+------------------------------------+---------------------------------------------------+
| network | | .. index:: |
| | | single: docker; attribute, network |
| | | single: attribute; network (docker) |
| | | single: network; docker attribute |
| | | single: podman; attribute, network |
| | | single: attribute; network (podman) |
| | | single: network; podman attribute |
| | | single: rkt; attribute, network |
| | | single: attribute; network (rkt) |
| | | single: network; rkt attribute |
| | | |
| | | If specified, this will be passed to the |
| | | ``docker run``, ``podman run``, or |
| | | ``rkt run`` command as the network setting |
| | | for the container. |
+-------------------+------------------------------------+---------------------------------------------------+
| run-command | ``/usr/sbin/pacemaker-remoted`` if | .. index:: |
| | bundle contains a **primitive**, | single: docker; attribute, run-command |
| | otherwise none | single: attribute; run-command (docker) |
| | | single: run-command; docker attribute |
| | | single: podman; attribute, run-command |
| | | single: attribute; run-command (podman) |
| | | single: run-command; podman attribute |
| | | single: rkt; attribute, run-command |
| | | single: attribute; run-command (rkt) |
| | | single: run-command; rkt attribute |
| | | |
| | | This command will be run inside the container |
| | | when launching it ("PID 1"). If the bundle |
| | | contains a **primitive**, this command *must* |
| | | start ``pacemaker-remoted`` (but could, for |
| | | example, be a script that does other stuff, too). |
+-------------------+------------------------------------+---------------------------------------------------+
| options | | .. index:: |
| | | single: docker; attribute, options |
| | | single: attribute; options (docker) |
| | | single: options; docker attribute |
| | | single: podman; attribute, options |
| | | single: attribute; options (podman) |
| | | single: options; podman attribute |
| | | single: rkt; attribute, options |
| | | single: attribute; options (rkt) |
| | | single: options; rkt attribute |
| | | |
| | | Extra command-line options to pass to the |
| | | ``docker run``, ``podman run``, or ``rkt run`` |
| | | command |
+-------------------+------------------------------------+---------------------------------------------------+
.. note::
Considerations when using cluster configurations or container images from
Pacemaker 1.1:
* If the container image has a pre-2.0.0 version of Pacemaker, set ``run-command``
to ``/usr/sbin/pacemaker_remoted`` (note the underbar instead of dash).
* ``masters`` is accepted as an alias for ``promoted-max``, but is deprecated since
2.0.0, and support for it will be removed in a future version.
Bundle Network Properties
_________________________
A bundle may optionally contain one ``<network>`` element.
.. index::
pair: XML element; network
single: resource; bundle
single: bundle; networking
.. topic:: **XML attributes of a network Element**
+----------------+---------+------------------------------------------------------------+
| Attribute | Default | Description |
+================+=========+============================================================+
| add-host | TRUE | .. index:: |
| | | single: network; attribute, add-host |
| | | single: attribute; add-host (network) |
| | | single: add-host; network attribute |
| | | |
| | | If TRUE, and ``ip-range-start`` is used, Pacemaker will |
| | | automatically ensure that ``/etc/hosts`` inside the |
| | | containers has entries for each |
| | | :ref:`replica name <s-resource-bundle-note-replica-names>` |
| | | and its assigned IP. |
+----------------+---------+------------------------------------------------------------+
| ip-range-start | | .. index:: |
| | | single: network; attribute, ip-range-start |
| | | single: attribute; ip-range-start (network) |
| | | single: ip-range-start; network attribute |
| | | |
| | | If specified, Pacemaker will create an implicit |
| | | ``ocf:heartbeat:IPaddr2`` resource for each container |
| | | instance, starting with this IP address, using up to |
| | | ``replicas`` sequential addresses. These addresses can be |
| | | used from the host's network to reach the service inside |
| | | the container, though it is not visible within the |
| | | container itself. Only IPv4 addresses are currently |
| | | supported. |
+----------------+---------+------------------------------------------------------------+
| host-netmask | 32 | .. index:: |
| | | single: network; attribute; host-netmask |
| | | single: attribute; host-netmask (network) |
| | | single: host-netmask; network attribute |
| | | |
| | | If ``ip-range-start`` is specified, the IP addresses |
| | | are created with this CIDR netmask (as a number of bits). |
+----------------+---------+------------------------------------------------------------+
| host-interface | | .. index:: |
| | | single: network; attribute; host-interface |
| | | single: attribute; host-interface (network) |
| | | single: host-interface; network attribute |
| | | |
| | | If ``ip-range-start`` is specified, the IP addresses are |
| | | created on this host interface (by default, it will be |
| | | determined from the IP address). |
+----------------+---------+------------------------------------------------------------+
| control-port | 3121 | .. index:: |
| | | single: network; attribute; control-port |
| | | single: attribute; control-port (network) |
| | | single: control-port; network attribute |
| | | |
| | | If the bundle contains a ``primitive``, the cluster will |
| | | use this integer TCP port for communication with |
| | | Pacemaker Remote inside the container. Changing this is |
| | | useful when the container is unable to listen on the |
| | | default port, for example, when the container uses the |
| | | host's network rather than ``ip-range-start`` (in which |
| | | case ``replicas-per-host`` must be 1), or when the bundle |
| | | may run on a Pacemaker Remote node that is already |
| | | listening on the default port. Any ``PCMK_remote_port`` |
| | | environment variable set on the host or in the container |
| | | is ignored for bundle connections. |
+----------------+---------+------------------------------------------------------------+
.. _s-resource-bundle-note-replica-names:
.. note::
Replicas are named by the bundle id plus a dash and an integer counter starting
with zero. For example, if a bundle named **httpd-bundle** has **replicas=2**, its
containers will be named **httpd-bundle-0** and **httpd-bundle-1**.
.. index::
pair: XML element; port-mapping
Additionally, a ``network`` element may optionally contain one or more
``port-mapping`` elements.
.. table:: **Attributes of a port-mapping Element**
+---------------+-------------------+------------------------------------------------------+
| Attribute | Default | Description |
+===============+===================+======================================================+
| id | | .. index:: |
| | | single: port-mapping; attribute, id |
| | | single: attribute; id (port-mapping) |
| | | single: id; port-mapping attribute |
| | | |
| | | A unique name for the port mapping (required) |
+---------------+-------------------+------------------------------------------------------+
| port | | .. index:: |
| | | single: port-mapping; attribute, port |
| | | single: attribute; port (port-mapping) |
| | | single: port; port-mapping attribute |
| | | |
| | | If this is specified, connections to this TCP port |
| | | number on the host network (on the container's |
| | | assigned IP address, if ``ip-range-start`` is |
| | | specified) will be forwarded to the container |
| | | network. Exactly one of ``port`` or ``range`` |
| | | must be specified in a ``port-mapping``. |
+---------------+-------------------+------------------------------------------------------+
| internal-port | value of ``port`` | .. index:: |
| | | single: port-mapping; attribute, internal-port |
| | | single: attribute; internal-port (port-mapping) |
| | | single: internal-port; port-mapping attribute |
| | | |
| | | If ``port`` and this are specified, connections |
| | | to ``port`` on the host's network will be |
| | | forwarded to this port on the container network. |
+---------------+-------------------+------------------------------------------------------+
| range | | .. index:: |
| | | single: port-mapping; attribute, range |
| | | single: attribute; range (port-mapping) |
| | | single: range; port-mapping attribute |
| | | |
| | | If this is specified, connections to these TCP |
| | | port numbers (expressed as *first_port*-*last_port*) |
| | | on the host network (on the container's assigned IP |
| | | address, if ``ip-range-start`` is specified) will |
| | | be forwarded to the same ports in the container |
| | | network. Exactly one of ``port`` or ``range`` |
| | | must be specified in a ``port-mapping``. |
+---------------+-------------------+------------------------------------------------------+
.. note::
If the bundle contains a ``primitive``, Pacemaker will automatically map the
``control-port``, so it is not necessary to specify that port in a
``port-mapping``.
.. index:
pair: XML element; storage
pair: XML element; storage-mapping
single: resource; bundle
.. _s-bundle-storage:
Bundle Storage Properties
_________________________
A bundle may optionally contain one ``storage`` element. A ``storage`` element
has no properties of its own, but may contain one or more ``storage-mapping``
elements.
.. table:: **Attributes of a storage-mapping Element**
+-----------------+---------+-------------------------------------------------------------+
| Attribute | Default | Description |
+=================+=========+=============================================================+
| id | | .. index:: |
| | | single: storage-mapping; attribute, id |
| | | single: attribute; id (storage-mapping) |
| | | single: id; storage-mapping attribute |
| | | |
| | | A unique name for the storage mapping (required) |
+-----------------+---------+-------------------------------------------------------------+
| source-dir | | .. index:: |
| | | single: storage-mapping; attribute, source-dir |
| | | single: attribute; source-dir (storage-mapping) |
| | | single: source-dir; storage-mapping attribute |
| | | |
| | | The absolute path on the host's filesystem that will be |
| | | mapped into the container. Exactly one of ``source-dir`` |
| | | and ``source-dir-root`` must be specified in a |
| | | ``storage-mapping``. |
+-----------------+---------+-------------------------------------------------------------+
| source-dir-root | | .. index:: |
| | | single: storage-mapping; attribute, source-dir-root |
| | | single: attribute; source-dir-root (storage-mapping) |
| | | single: source-dir-root; storage-mapping attribute |
| | | |
| | | The start of a path on the host's filesystem that will |
| | | be mapped into the container, using a different |
| | | subdirectory on the host for each container instance. |
| | | The subdirectory will be named the same as the |
| | | :ref:`replica name <s-resource-bundle-note-replica-names>`. |
| | | Exactly one of ``source-dir`` and ``source-dir-root`` |
| | | must be specified in a ``storage-mapping``. |
+-----------------+---------+-------------------------------------------------------------+
| target-dir | | .. index:: |
| | | single: storage-mapping; attribute, target-dir |
| | | single: attribute; target-dir (storage-mapping) |
| | | single: target-dir; storage-mapping attribute |
| | | |
| | | The path name within the container where the host |
| | | storage will be mapped (required) |
+-----------------+---------+-------------------------------------------------------------+
| options | | .. index:: |
| | | single: storage-mapping; attribute, options |
| | | single: attribute; options (storage-mapping) |
| | | single: options; storage-mapping attribute |
| | | |
| | | A comma-separated list of file system mount |
| | | options to use when mapping the storage |
+-----------------+---------+-------------------------------------------------------------+
.. note::
Pacemaker does not define the behavior if the source directory does not already
exist on the host. However, it is expected that the container technology and/or
its resource agent will create the source directory in that case.
.. note::
If the bundle contains a ``primitive``,
Pacemaker will automatically map the equivalent of
``source-dir=/etc/pacemaker/authkey target-dir=/etc/pacemaker/authkey``
and ``source-dir-root=/var/log/pacemaker/bundles target-dir=/var/log`` into the
container, so it is not necessary to specify those paths in a
``storage-mapping``.
.. important::
The ``PCMK_authkey_location`` environment variable must not be set to anything
other than the default of ``/etc/pacemaker/authkey`` on any node in the cluster.
.. important::
If SELinux is used in enforcing mode on the host, you must ensure the container
is allowed to use any storage you mount into it. For Docker and podman bundles,
adding "Z" to the mount options will create a container-specific label for the
mount that allows the container access.
.. index::
single: resource; bundle
Bundle Primitive
________________
A bundle may optionally contain one :ref:`primitive <primitive-resource>`
resource. The primitive may have operations, instance attributes, and
meta-attributes defined, as usual.
If a bundle contains a primitive resource, the container image must include
the Pacemaker Remote daemon, and at least one of ``ip-range-start`` or
``control-port`` must be configured in the bundle. Pacemaker will create an
implicit **ocf:pacemaker:remote** resource for the connection, launch
Pacemaker Remote within the container, and monitor and manage the primitive
resource via Pacemaker Remote.
If the bundle has more than one container instance (replica), the primitive
resource will function as an implicit :ref:`clone <s-resource-clone>` -- a
:ref:`promotable clone <s-resource-promotable>` if the bundle has ``promoted-max``
greater than zero.
.. note::
If you want to pass environment variables to a bundle's Pacemaker Remote
connection or primitive, you have two options:
* Environment variables whose value is the same regardless of the underlying host
may be set using the container element's ``options`` attribute.
* If you want variables to have host-specific values, you can use the
:ref:`storage-mapping <s-bundle-storage>` element to map a file on the host as
``/etc/pacemaker/pcmk-init.env`` in the container *(since 2.0.3)*.
Pacemaker Remote will parse this file as a shell-like format, with
variables set as NAME=VALUE, ignoring blank lines and comments starting
with "#".
.. important::
When a bundle has a ``primitive``, Pacemaker on all cluster nodes must be able to
contact Pacemaker Remote inside the bundle's containers.
* The containers must have an accessible network (for example, ``network`` should
not be set to "none" with a ``primitive``).
* The default, using a distinct network space inside the container, works in
combination with ``ip-range-start``. Any firewall must allow access from all
cluster nodes to the ``control-port`` on the container IPs.
* If the container shares the host's network space (for example, by setting
``network`` to "host"), a unique ``control-port`` should be specified for each
bundle. Any firewall must allow access from all cluster nodes to the
``control-port`` on all cluster and remote node IPs.
.. index::
single: resource; bundle
.. _s-bundle-attributes:
Bundle Node Attributes
______________________
If the bundle has a ``primitive``, the primitive's resource agent may want to set
node attributes such as :ref:`promotion scores <s-promotion-scores>`. However, with
containers, it is not apparent which node should get the attribute.
If the container uses shared storage that is the same no matter which node the
container is hosted on, then it is appropriate to use the promotion score on the
bundle node itself.
On the other hand, if the container uses storage exported from the underlying host,
then it may be more appropriate to use the promotion score on the underlying host.
Since this depends on the particular situation, the
``container-attribute-target`` resource meta-attribute allows the user to specify
which approach to use. If it is set to ``host``, then user-defined node attributes
will be checked on the underlying host. If it is anything else, the local node
(in this case the bundle node) is used as usual.
This only applies to user-defined attributes; the cluster will always check the
local node for cluster-defined attributes such as ``#uname``.
If ``container-attribute-target`` is ``host``, the cluster will pass additional
environment variables to the primitive's resource agent that allow it to set
node attributes appropriately: ``CRM_meta_container_attribute_target`` (identical
to the meta-attribute value) and ``CRM_meta_physical_host`` (the name of the
underlying host).
.. note::
When called by a resource agent, the ``attrd_updater`` and ``crm_attribute``
commands will automatically check those environment variables and set
attributes appropriately.
.. index::
single: resource; bundle
Bundle Meta-Attributes
______________________
Any meta-attribute set on a bundle will be inherited by the bundle's
primitive and any resources implicitly created by Pacemaker for the bundle.
This includes options such as ``priority``, ``target-role``, and ``is-managed``. See
:ref:`resource_options` for more information.
Limitations of Bundles
______________________
Restarting pacemaker while a bundle is unmanaged or the cluster is in
maintenance mode may cause the bundle to fail.
Bundles may not be explicitly cloned or included in groups. This includes the
bundle's primitive and any resources implicitly created by Pacemaker for the
bundle. (If ``replicas`` is greater than 1, the bundle will behave like a clone
implicitly.)
Bundles do not have instance attributes, utilization attributes, or operations,
though a bundle's primitive may have them.
A bundle with a primitive can run on a Pacemaker Remote node only if the bundle
uses a distinct ``control-port``.
.. [#] Of course, the service must support running multiple instances.
.. [#] These are historical terms that will eventually be replaced, but the extensive
use of them and the need for backward compatibility makes it a long process.
You may see examples using a **master** tag instead of a **clone** tag with the
**promotable** meta-attribute set to **true**; the **master** tag is supported, but
deprecated, and will be removed in a future version. You may also see such
services referred to as *multi-state* or *stateful*; these mean the same thing
as *promotable*.
.. [#] Docker is a trademark of Docker, Inc. No endorsement by or association with
Docker, Inc. is implied.
diff --git a/doc/sphinx/Pacemaker_Explained/constraints.rst b/doc/sphinx/Pacemaker_Explained/constraints.rst
index c321eb971b..c917c79966 100644
--- a/doc/sphinx/Pacemaker_Explained/constraints.rst
+++ b/doc/sphinx/Pacemaker_Explained/constraints.rst
@@ -1,986 +1,1027 @@
.. index::
single: constraint
single: resource; constraint
.. _constraints:
Resource Constraints
--------------------
.. index::
single: resource; score
single: node; score
Scores
######
Scores of all kinds are integral to how the cluster works.
Practically everything from moving a resource to deciding which
resource to stop in a degraded cluster is achieved by manipulating
scores in some way.
Scores are calculated per resource and node. Any node with a
negative score for a resource can't run that resource. The cluster
places a resource on the node with the highest score for it.
Infinity Math
_____________
Pacemaker implements **INFINITY** (or equivalently, **+INFINITY**) internally as a
score of 1,000,000. Addition and subtraction with it follow these three basic
rules:
* Any value + **INFINITY** = **INFINITY**
* Any value - **INFINITY** = -**INFINITY**
* **INFINITY** - **INFINITY** = **-INFINITY**
.. note::
What if you want to use a score higher than 1,000,000? Typically this possibility
arises when someone wants to base the score on some external metric that might
go above 1,000,000.
The short answer is you can't.
The long answer is it is sometimes possible work around this limitation
creatively. You may be able to set the score to some computed value based on
the external metric rather than use the metric directly. For nodes, you can
store the metric as a node attribute, and query the attribute when computing
the score (possibly as part of a custom resource agent).
.. _location-constraint:
.. index::
single: location constraint
single: constraint; location
Deciding Which Nodes a Resource Can Run On
##########################################
*Location constraints* tell the cluster which nodes a resource can run on.
There are two alternative strategies. One way is to say that, by default,
resources can run anywhere, and then the location constraints specify nodes
that are not allowed (an *opt-out* cluster). The other way is to start with
nothing able to run anywhere, and use location constraints to selectively
enable allowed nodes (an *opt-in* cluster).
Whether you should choose opt-in or opt-out depends on your
personal preference and the make-up of your cluster. If most of your
resources can run on most of the nodes, then an opt-out arrangement is
likely to result in a simpler configuration. On the other-hand, if
most resources can only run on a small subset of nodes, an opt-in
configuration might be simpler.
.. index::
pair: XML element; rsc_location
- single: constraint; location
single: constraint; rsc_location
Location Properties
___________________
.. table:: **Attributes of a rsc_location Element**
+--------------------+---------+----------------------------------------------------------------------------------------------+
| Attribute | Default | Description |
+====================+=========+==============================================================================================+
| id | | .. index:: |
| | | single: rsc_location; attribute, id |
| | | single: attribute; id (rsc_location) |
| | | single: id; rsc_location attribute |
| | | |
| | | A unique name for the constraint (required) |
+--------------------+---------+----------------------------------------------------------------------------------------------+
| rsc | | .. index:: |
| | | single: rsc_location; attribute, rsc |
| | | single: attribute; rsc (rsc_location) |
| | | single: rsc; rsc_location attribute |
| | | |
| | | The name of the resource to which this constraint |
| | | applies. A location constraint must either have a |
| | | ``rsc``, have a ``rsc-pattern``, or contain at |
| | | least one resource set. |
+--------------------+---------+----------------------------------------------------------------------------------------------+
| rsc-pattern | | .. index:: |
| | | single: rsc_location; attribute, rsc-pattern |
| | | single: attribute; rsc-pattern (rsc_location) |
| | | single: rsc-pattern; rsc_location attribute |
| | | |
| | | A pattern matching the names of resources to which |
| | | this constraint applies. The syntax is the same as |
| | | `POSIX <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04>`_ |
| | | extended regular expressions, with the addition of an |
| | | initial *!* indicating that resources *not* matching |
| | | the pattern are selected. If the regular expression |
| | | contains submatches, and the constraint is governed by |
| | | a :ref:`rule <rules>`, the submatches can be |
| | | referenced as **%0** through **%9** in the rule's |
| | | ``score-attribute`` or a rule expression's ``attribute``. |
| | | A location constraint must either have a ``rsc``, have a |
| | | ``rsc-pattern``, or contain at least one resource set. |
+--------------------+---------+----------------------------------------------------------------------------------------------+
| node | | .. index:: |
| | | single: rsc_location; attribute, node |
| | | single: attribute; node (rsc_location) |
| | | single: node; rsc_location attribute |
| | | |
| | | The name of the node to which this constraint applies. |
| | | A location constraint must either have a ``node`` and |
| | | ``score``, or contain at least one rule. |
+--------------------+---------+----------------------------------------------------------------------------------------------+
| score | | .. index:: |
| | | single: rsc_location; attribute, score |
| | | single: attribute; score (rsc_location) |
| | | single: score; rsc_location attribute |
| | | |
| | | Positive values indicate a preference for running the |
| | | affected resource(s) on ``node`` -- the higher the value, |
| | | the stronger the preference. Negative values indicate |
| | | the resource(s) should avoid this node (a value of |
| | | **-INFINITY** changes "should" to "must"). A location |
| | | constraint must either have a ``node`` and ``score``, |
| | | or contain at least one rule. |
+--------------------+---------+----------------------------------------------------------------------------------------------+
| resource-discovery | always | .. index:: |
| | | single: rsc_location; attribute, resource-discovery |
| | | single: attribute; resource-discovery (rsc_location) |
| | | single: resource-discovery; rsc_location attribute |
| | | |
| | | Whether Pacemaker should perform resource discovery |
| | | (that is, check whether the resource is already running) |
| | | for this resource on this node. This should normally be |
| | | left as the default, so that rogue instances of a |
| | | service can be stopped when they are running where they |
| | | are not supposed to be. However, there are two |
| | | situations where disabling resource discovery is a good |
| | | idea: when a service is not installed on a node, |
| | | discovery might return an error (properly written OCF |
| | | agents will not, so this is usually only seen with other |
| | | agent types); and when Pacemaker Remote is used to scale |
| | | a cluster to hundreds of nodes, limiting resource |
| | | discovery to allowed nodes can significantly boost |
| | | performance. |
| | | |
| | | * ``always:`` Always perform resource discovery for |
| | | the specified resource on this node. |
| | | |
| | | * ``never:`` Never perform resource discovery for the |
| | | specified resource on this node. This option should |
| | | generally be used with a -INFINITY score, although |
| | | that is not strictly required. |
| | | |
| | | * ``exclusive:`` Perform resource discovery for the |
| | | specified resource only on this node (and other nodes |
| | | similarly marked as ``exclusive``). Multiple location |
| | | constraints using ``exclusive`` discovery for the |
| | | same resource across different nodes creates a subset |
| | | of nodes resource-discovery is exclusive to. If a |
| | | resource is marked for ``exclusive`` discovery on one |
| | | or more nodes, that resource is only allowed to be |
| | | placed within that subset of nodes. |
+--------------------+---------+----------------------------------------------------------------------------------------------+
.. warning::
Setting ``resource-discovery`` to ``never`` or ``exclusive`` removes Pacemaker's
ability to detect and stop unwanted instances of a service running
where it's not supposed to be. It is up to the system administrator (you!)
to make sure that the service can *never* be active on nodes without
``resource-discovery`` (such as by leaving the relevant software uninstalled).
.. index::
single: Asymmetrical Clusters
single: Opt-In Clusters
Asymmetrical "Opt-In" Clusters
______________________________
To create an opt-in cluster, start by preventing resources from running anywhere
by default:
.. code-block:: none
# crm_attribute --name symmetric-cluster --update false
Then start enabling nodes. The following fragment says that the web
server prefers **sles-1**, the database prefers **sles-2** and both can
fail over to **sles-3** if their most preferred node fails.
.. topic:: Opt-in location constraints for two resources
.. code-block:: xml
<constraints>
<rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="200"/>
<rsc_location id="loc-2" rsc="Webserver" node="sles-3" score="0"/>
<rsc_location id="loc-3" rsc="Database" node="sles-2" score="200"/>
<rsc_location id="loc-4" rsc="Database" node="sles-3" score="0"/>
</constraints>
.. index::
single: Symmetrical Clusters
single: Opt-Out Clusters
Symmetrical "Opt-Out" Clusters
______________________________
To create an opt-out cluster, start by allowing resources to run
anywhere by default:
.. code-block:: none
# crm_attribute --name symmetric-cluster --update true
Then start disabling nodes. The following fragment is the equivalent
of the above opt-in configuration.
.. topic:: Opt-out location constraints for two resources
.. code-block:: xml
<constraints>
<rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="200"/>
<rsc_location id="loc-2-do-not-run" rsc="Webserver" node="sles-2" score="-INFINITY"/>
<rsc_location id="loc-3-do-not-run" rsc="Database" node="sles-1" score="-INFINITY"/>
<rsc_location id="loc-4" rsc="Database" node="sles-2" score="200"/>
</constraints>
.. _node-score-equal:
What if Two Nodes Have the Same Score
_____________________________________
If two nodes have the same score, then the cluster will choose one.
This choice may seem random and may not be what was intended, however
the cluster was not given enough information to know any better.
.. topic:: Constraints where a resource prefers two nodes equally
.. code-block:: xml
<constraints>
<rsc_location id="loc-1" rsc="Webserver" node="sles-1" score="INFINITY"/>
<rsc_location id="loc-2" rsc="Webserver" node="sles-2" score="INFINITY"/>
<rsc_location id="loc-3" rsc="Database" node="sles-1" score="500"/>
<rsc_location id="loc-4" rsc="Database" node="sles-2" score="300"/>
<rsc_location id="loc-5" rsc="Database" node="sles-2" score="200"/>
</constraints>
In the example above, assuming no other constraints and an inactive
cluster, **Webserver** would probably be placed on **sles-1** and **Database** on
**sles-2**. It would likely have placed **Webserver** based on the node's
uname and **Database** based on the desire to spread the resource load
evenly across the cluster. However other factors can also be involved
in more complex configurations.
.. index::
single: constraint; ordering
single: resource; start order
.. _s-resource-ordering:
Specifying the Order in which Resources Should Start/Stop
#########################################################
*Ordering constraints* tell the cluster the order in which certain
resource actions should occur.
.. important::
Ordering constraints affect *only* the ordering of resource actions;
they do *not* require that the resources be placed on the
same node. If you want resources to be started on the same node
*and* in a specific order, you need both an ordering constraint *and*
a colocation constraint (see :ref:`s-resource-colocation`), or
alternatively, a group (see :ref:`group-resources`).
.. index::
pair: XML element; rsc_order
- pair: constraint; ordering
+ pair: constraint; rsc_order
Ordering Properties
___________________
.. table:: **Attributes of a rsc_order Element**
+--------------+----------------------------+-------------------------------------------------------------------+
| Field | Default | Description |
+==============+============================+===================================================================+
| id | | .. index:: |
| | | single: rsc_order; attribute, id |
| | | single: attribute; id (rsc_order) |
| | | single: id; rsc_order attribute |
| | | |
| | | A unique name for the constraint |
+--------------+----------------------------+-------------------------------------------------------------------+
| first | | .. index:: |
| | | single: rsc_order; attribute, first |
| | | single: attribute; first (rsc_order) |
| | | single: first; rsc_order attribute |
| | | |
| | | Name of the resource that the ``then`` resource |
| | | depends on |
+--------------+----------------------------+-------------------------------------------------------------------+
| then | | .. index:: |
| | | single: rsc_order; attribute, then |
| | | single: attribute; then (rsc_order) |
| | | single: then; rsc_order attribute |
| | | |
| | | Name of the dependent resource |
+--------------+----------------------------+-------------------------------------------------------------------+
| first-action | start | .. index:: |
| | | single: rsc_order; attribute, first-action |
| | | single: attribute; first-action (rsc_order) |
| | | single: first-action; rsc_order attribute |
| | | |
| | | The action that the ``first`` resource must complete |
| | | before ``then-action`` can be initiated for the ``then`` |
| | | resource. Allowed values: ``start``, ``stop``, |
| | | ``promote``, ``demote``. |
+--------------+----------------------------+-------------------------------------------------------------------+
| then-action | value of ``first-action`` | .. index:: |
| | | single: rsc_order; attribute, then-action |
| | | single: attribute; then-action (rsc_order) |
| | | single: first-action; rsc_order attribute |
| | | |
| | | The action that the ``then`` resource can execute only |
| | | after the ``first-action`` on the ``first`` resource has |
| | | completed. Allowed values: ``start``, ``stop``, |
| | | ``promote``, ``demote``. |
+--------------+----------------------------+-------------------------------------------------------------------+
| kind | Mandatory | .. index:: |
| | | single: rsc_order; attribute, kind |
| | | single: attribute; kind (rsc_order) |
| | | single: kind; rsc_order attribute |
| | | |
| | | How to enforce the constraint. Allowed values: |
| | | |
| | | * ``Mandatory:`` ``then-action`` will never be initiated |
| | | for the ``then`` resource unless and until ``first-action`` |
| | | successfully completes for the ``first`` resource. |
| | | |
| | | * ``Optional:`` The constraint applies only if both specified |
| | | resource actions are scheduled in the same transition |
| | | (that is, in response to the same cluster state). This |
| | | means that ``then-action`` is allowed on the ``then`` |
| | | resource regardless of the state of the ``first`` resource, |
| | | but if both actions happen to be scheduled at the same time, |
| | | they will be ordered. |
| | | |
| | | * ``Serialize:`` Ensure that the specified actions are never |
| | | performed concurrently for the specified resources. |
| | | ``First-action`` and ``then-action`` can be executed in either |
| | | order, but one must complete before the other can be initiated. |
| | | An example use case is when resource start-up puts a high load |
| | | on the host. |
+--------------+----------------------------+-------------------------------------------------------------------+
| symmetrical | TRUE for ``Mandatory`` and | .. index:: |
| | ``Optional`` kinds. FALSE | single: rsc_order; attribute, symmetrical |
| | for ``Serialize`` kind. | single: attribute; symmetrical (rsc)order) |
| | | single: symmetrical; rsc_order attribute |
| | | |
| | | If true, the reverse of the constraint applies for the |
| | | opposite action (for example, if B starts after A starts, |
| | | then B stops before A stops). ``Serialize`` orders cannot |
| | | be symmetrical. |
+--------------+----------------------------+-------------------------------------------------------------------+
``Promote`` and ``demote`` apply to the master role of :ref:`promotable <s-resource-promotable>`
resources.
Optional and mandatory ordering
_______________________________
Here is an example of ordering constraints where **Database** *must* start before
**Webserver**, and **IP** *should* start before **Webserver** if they both need to be
started:
.. topic:: Optional and mandatory ordering constraints
.. code-block:: xml
<constraints>
<rsc_order id="order-1" first="IP" then="Webserver" kind="Optional"/>
<rsc_order id="order-2" first="Database" then="Webserver" kind="Mandatory" />
</constraints>
Because the above example lets ``symmetrical`` default to TRUE, **Webserver**
must be stopped before **Database** can be stopped, and **Webserver** should be
stopped before **IP** if they both need to be stopped.
.. index::
+ single: colocation
single: constraint; colocation
single: resource; location relative to other resources
.. _s-resource-colocation:
Placing Resources Relative to other Resources
#############################################
*Colocation constraints* tell the cluster that the location of one resource
depends on the location of another one.
Colocation has an important side-effect: it affects the order in which
resources are assigned to a node. Think about it: You can't place A relative to
B unless you know where B is [#]_.
So when you are creating colocation constraints, it is important to
consider whether you should colocate A with B, or B with A.
-Another thing to keep in mind is that, assuming A is colocated with
-B, the cluster will take into account A's preferences when
-deciding which node to choose for B.
-
-For a detailed look at exactly how this occurs, see
-`Colocation Explained <http://clusterlabs.org/doc/Colocation_Explained.pdf>`_.
-
.. important::
Colocation constraints affect *only* the placement of resources; they do *not*
require that the resources be started in a particular order. If you want
resources to be started on the same node *and* in a specific order, you need
both an ordering constraint (see :ref:`s-resource-ordering`) *and* a colocation
constraint, or alternatively, a group (see :ref:`group-resources`).
.. index::
pair: XML element; rsc_colocation
- pair: constraint; colocation
+ single: constraint; rsc_colocation
Colocation Properties
_____________________
.. table:: **Attributes of a rsc_colocation Constraint**
+----------------+---------+--------------------------------------------------------+
| Field | Default | Description |
+================+=========+========================================================+
| id | | .. index:: |
| | | single: rsc_colocation; attribute, id |
| | | single: attribute; id (rsc_colocation) |
| | | single: id; rsc_colocation attribute |
| | | |
| | | A unique name for the constraint (required). |
+----------------+---------+--------------------------------------------------------+
| rsc | | .. index:: |
| | | single: rsc_colocation; attribute, rsc |
| | | single: attribute; rsc (rsc_colocation) |
| | | single: rsc; rsc_colocation attribute |
| | | |
| | | The name of a resource that should be located |
- | | | relative to ``with-rsc`` (required). |
+ | | | relative to ``with-rsc``. A colocation constraint must |
+ | | | either contain at least one |
+ | | | :ref:`resource set <s-resource-sets>`, or specify both |
+ | | | ``rsc`` and ``with-rsc``. |
+----------------+---------+--------------------------------------------------------+
| with-rsc | | .. index:: |
| | | single: rsc_colocation; attribute, with-rsc |
| | | single: attribute; with-rsc (rsc_colocation) |
| | | single: with-rsc; rsc_colocation attribute |
| | | |
| | | The name of the resource used as the colocation |
| | | target. The cluster will decide where to put this |
- | | | resource first and then decide where to put |
- | | | ``rsc`` (required). |
+ | | | resource first and then decide where to put ``rsc``. |
+ | | | A colocation constraint must either contain at least |
+ | | | one :ref:`resource set <s-resource-sets>`, or specify |
+ | | | both ``rsc`` and ``with-rsc``. |
+----------------+---------+--------------------------------------------------------+
| node-attribute | #uname | .. index:: |
| | | single: rsc_colocation; attribute, node-attribute |
| | | single: attribute; node-attribute (rsc_colocation) |
| | | single: node-attribute; rsc_colocation attribute |
| | | |
- | | | The node attribute that must be the same on the |
- | | | node running ``rsc`` and the node running ``with-rsc`` |
- | | | for the constraint to be satisfied. (For details, |
- | | | see :ref:`s-coloc-attribute`.) |
+ | | | If ``rsc`` and ``with-rsc`` are specified, this node |
+ | | | attribute must be the same on the node running ``rsc`` |
+ | | | and the node running ``with-rsc`` for the constraint |
+ | | | to be satisfied. (For details, see |
+ | | | :ref:`s-coloc-attribute`.) |
+----------------+---------+--------------------------------------------------------+
- | score | | .. index:: |
+ | score | 0 | .. index:: |
| | | single: rsc_colocation; attribute, score |
| | | single: attribute; score (rsc_colocation) |
| | | single: score; rsc_colocation attribute |
| | | |
| | | Positive values indicate the resources should run on |
| | | the same node. Negative values indicate the resources |
| | | should run on different nodes. Values of |
- | | | +/- **INFINITY** change "should" to "must". |
+ | | | +/- ``INFINITY`` change "should" to "must". |
+ +----------------+---------+--------------------------------------------------------+
+ | rsc-role | Started | .. index:: |
+ | | | single: clone; ordering constraint, rsc-role |
+ | | | single: ordering constraint; rsc-role (clone) |
+ | | | single: rsc-role; clone ordering constraint |
+ | | | |
+ | | | If ``rsc`` and ``with-rsc`` are specified, and ``rsc`` |
+ | | | is a :ref:`promotable clone <s-resource-promotable>`, |
+ | | | the constraint applies only to ``rsc`` instances in |
+ | | | this role. Allowed values: ``Started``, ``Master``, |
+ | | | ``Slave``. For details, see |
+ | | | :ref:`promotable-clone-constraints`. |
+ +----------------+---------+--------------------------------------------------------+
+ | with-rsc-role | Started | .. index:: |
+ | | | single: clone; ordering constraint, with-rsc-role |
+ | | | single: ordering constraint; with-rsc-role (clone) |
+ | | | single: with-rsc-role; clone ordering constraint |
+ | | | |
+ | | | If ``rsc`` and ``with-rsc`` are specified, and |
+ | | | ``with-rsc`` is a |
+ | | | :ref:`promotable clone <s-resource-promotable>`, the |
+ | | | constraint applies only to ``with-rsc`` instances in |
+ | | | this role. Allowed values: ``Started``, ``Master``, |
+ | | | ``Slave``. For details, see |
+ | | | :ref:`promotable-clone-constraints`. |
+----------------+---------+--------------------------------------------------------+
Mandatory Placement
___________________
Mandatory placement occurs when the constraint's score is
**+INFINITY** or **-INFINITY**. In such cases, if the constraint can't be
satisfied, then the **rsc** resource is not permitted to run. For
``score=INFINITY``, this includes cases where the ``with-rsc`` resource is
not active.
If you need resource **A** to always run on the same machine as
resource **B**, you would add the following constraint:
.. topic:: Mandatory colocation constraint for two resources
.. code-block:: xml
<rsc_colocation id="colocate" rsc="A" with-rsc="B" score="INFINITY"/>
Remember, because **INFINITY** was used, if **B** can't run on any
of the cluster nodes (for whatever reason) then **A** will not
be allowed to run. Whether **A** is running or not has no effect on **B**.
Alternatively, you may want the opposite -- that **A** *cannot*
run on the same machine as **B**. In this case, use ``score="-INFINITY"``.
.. topic:: Mandatory anti-colocation constraint for two resources
.. code-block:: xml
<rsc_colocation id="anti-colocate" rsc="A" with-rsc="B" score="-INFINITY"/>
Again, by specifying **-INFINITY**, the constraint is binding. So if the
only place left to run is where **B** already is, then **A** may not run anywhere.
As with **INFINITY**, **B** can run even if **A** is stopped. However, in this
case **A** also can run if **B** is stopped, because it still meets the
constraint of **A** and **B** not running on the same node.
Advisory Placement
__________________
If mandatory placement is about "must" and "must not", then advisory
placement is the "I'd prefer if" alternative. For constraints with
scores greater than **-INFINITY** and less than **INFINITY**, the cluster
will try to accommodate your wishes but may ignore them if the
alternative is to stop some of the cluster resources.
As in life, where if enough people prefer something it effectively
becomes mandatory, advisory colocation constraints can combine with
other elements of the configuration to behave as if they were
mandatory.
.. topic:: Advisory colocation constraint for two resources
.. code-block:: xml
<rsc_colocation id="colocate-maybe" rsc="A" with-rsc="B" score="500"/>
.. _s-coloc-attribute:
Colocation by Node Attribute
____________________________
The ``node-attribute`` property of a colocation constraints allows you to express
the requirement, "these resources must be on similar nodes".
As an example, imagine that you have two Storage Area Networks (SANs) that are
not controlled by the cluster, and each node is connected to one or the other.
You may have two resources **r1** and **r2** such that **r2** needs to use the same
SAN as **r1**, but doesn't necessarily have to be on the same exact node.
In such a case, you could define a :ref:`node attribute <node_attributes>` named
**san**, with the value **san1** or **san2** on each node as appropriate. Then, you
could colocate **r2** with **r1** using ``node-attribute`` set to **san**.
+.. _s-coloc-influence:
+
+Colocation Influence
+____________________
+
+If A is colocated with B, the cluster will take into account A's preferences
+when deciding where to place B, to maximize the chance that both resources can
+run.
+
+For a detailed look at exactly how this occurs, see
+`Colocation Explained <http://clusterlabs.org/doc/Colocation_Explained.pdf>`_.
+
+
.. _s-resource-sets:
Resource Sets
#############
.. index::
single: constraint; resource set
single: resource; resource set
*Resource sets* allow multiple resources to be affected by a single constraint.
.. topic:: A set of 3 resources
.. code-block:: xml
<resource_set id="resource-set-example">
<resource_ref id="A"/>
<resource_ref id="B"/>
<resource_ref id="C"/>
</resource_set>
Resource sets are valid inside ``rsc_location``, ``rsc_order``
(see :ref:`s-resource-sets-ordering`), ``rsc_colocation``
(see :ref:`s-resource-sets-colocation`), and ``rsc_ticket``
(see :ref:`ticket-constraints`) constraints.
A resource set has a number of properties that can be set, though not all
have an effect in all contexts.
.. index::
pair: XML element; resource_set
.. topic:: **Attributes of a resource_set Element**
- +-------------+---------+--------------------------------------------------------+
- | Field | Default | Description |
- +=============+=========+========================================================+
- | id | | .. index:: |
- | | | single: resource_set; attribute, id |
- | | | single: attribute; id (resource_set) |
- | | | single: id; resource_set attribute |
- | | | |
- | | | A unique name for the set |
- +-------------+---------+--------------------------------------------------------+
- | sequential | true | .. index:: |
- | | | single: resource_set; attribute, sequential |
- | | | single: attribute; sequential (resource_set) |
- | | | single: sequential; resource_set attribute |
- | | | |
- | | | Whether the members of the set must be acted on in |
- | | | order. Meaningful within ``rsc_order`` and |
- | | | ``rsc_colocation``. |
- +-------------+---------+--------------------------------------------------------+
- | require-all | true | .. index:: |
- | | | single: resource_set; attribute, require-all |
- | | | single: attribute; require-all (resource_set) |
- | | | single: require-all; resource_set attribute |
- | | | |
- | | | Whether all members of the set must be active before |
- | | | continuing. With the current implementation, the |
- | | | cluster may continue even if only one member of the |
- | | | set is started, but if more than one member of the set |
- | | | is starting at the same time, the cluster will still |
- | | | wait until all of those have started before continuing |
- | | | (this may change in future versions). Meaningful |
- | | | within ``rsc_order``. |
- +-------------+---------+--------------------------------------------------------+
- | role | | .. index:: |
- | | | single: resource_set; attribute, role |
- | | | single: attribute; role (resource_set) |
- | | | single: role; resource_set attribute |
- | | | |
- | | | Limit the effect of the constraint to the specified |
- | | | role. Meaningful within ``rsc_location``, |
- | | | ``rsc_colocation`` and ``rsc_ticket``. |
- +-------------+---------+--------------------------------------------------------+
- | action | | .. index:: |
- | | | single: resource_set; attribute, action |
- | | | single: attribute; action (resource_set) |
- | | | single: action; resource_set attribute |
- | | | |
- | | | Limit the effect of the constraint to the specified |
- | | | action. Meaningful within ``rsc_order``. |
- +-------------+---------+--------------------------------------------------------+
- | score | | .. index:: |
- | | | single: resource_set; attribute, score |
- | | | single: attribute; score (resource_set) |
- | | | single: score; resource_set attribute |
- | | | |
- | | | *Advanced use only.* Use a specific score for this |
- | | | set within the constraint. |
- +-------------+---------+--------------------------------------------------------+
+ +-------------+------------------+--------------------------------------------------------+
+ | Field | Default | Description |
+ +=============+==================+========================================================+
+ | id | | .. index:: |
+ | | | single: resource_set; attribute, id |
+ | | | single: attribute; id (resource_set) |
+ | | | single: id; resource_set attribute |
+ | | | |
+ | | | A unique name for the set (required) |
+ +-------------+------------------+--------------------------------------------------------+
+ | sequential | true | .. index:: |
+ | | | single: resource_set; attribute, sequential |
+ | | | single: attribute; sequential (resource_set) |
+ | | | single: sequential; resource_set attribute |
+ | | | |
+ | | | Whether the members of the set must be acted on in |
+ | | | order. Meaningful within ``rsc_order`` and |
+ | | | ``rsc_colocation``. |
+ +-------------+------------------+--------------------------------------------------------+
+ | require-all | true | .. index:: |
+ | | | single: resource_set; attribute, require-all |
+ | | | single: attribute; require-all (resource_set) |
+ | | | single: require-all; resource_set attribute |
+ | | | |
+ | | | Whether all members of the set must be active before |
+ | | | continuing. With the current implementation, the |
+ | | | cluster may continue even if only one member of the |
+ | | | set is started, but if more than one member of the set |
+ | | | is starting at the same time, the cluster will still |
+ | | | wait until all of those have started before continuing |
+ | | | (this may change in future versions). Meaningful |
+ | | | within ``rsc_order``. |
+ +-------------+------------------+--------------------------------------------------------+
+ | role | | .. index:: |
+ | | | single: resource_set; attribute, role |
+ | | | single: attribute; role (resource_set) |
+ | | | single: role; resource_set attribute |
+ | | | |
+ | | | The constraint applies only to resource set members |
+ | | | that are :ref:`s-resource-promotable` in this |
+ | | | role. Meaningful within ``rsc_location``, |
+ | | | ``rsc_colocation`` and ``rsc_ticket``. |
+ | | | Allowed values: ``Started``, ``Master``, ``Slave``. |
+ | | | For details, see :ref:`promotable-clone-constraints`. |
+ +-------------+------------------+--------------------------------------------------------+
+ | action | value of | .. index:: |
+ | | ``first-action`` | single: resource_set; attribute, action |
+ | | in the enclosing | single: attribute; action (resource_set) |
+ | | ordering | single: action; resource_set attribute |
+ | | constraint | |
+ | | | The action that applies to *all members* of the set. |
+ | | | Meaningful within ``rsc_order``. Allowed values: |
+ | | | ``start``, ``stop``, ``promote``, ``demote``. |
+ +-------------+------------------+--------------------------------------------------------+
+ | score | | .. index:: |
+ | | | single: resource_set; attribute, score |
+ | | | single: attribute; score (resource_set) |
+ | | | single: score; resource_set attribute |
+ | | | |
+ | | | *Advanced use only.* Use a specific score for this |
+ | | | set within the constraint. |
+ +-------------+------------------+--------------------------------------------------------+
.. _s-resource-sets-ordering:
Ordering Sets of Resources
##########################
A common situation is for an administrator to create a chain of ordered
resources, such as:
.. topic:: A chain of ordered resources
.. code-block:: xml
<constraints>
<rsc_order id="order-1" first="A" then="B" />
<rsc_order id="order-2" first="B" then="C" />
<rsc_order id="order-3" first="C" then="D" />
</constraints>
.. topic:: Visual representation of the four resources' start order for the above constraints
.. image:: images/resource-set.png
:alt: Ordered set
Ordered Set
___________
-To simplify this situation, resource sets (see :ref:`s-resource-sets`) can be used
-within ordering constraints:
+To simplify this situation, :ref:`s-resource-sets` can be used within ordering
+constraints:
.. topic:: A chain of ordered resources expressed as a set
.. code-block:: xml
<constraints>
<rsc_order id="order-1">
<resource_set id="ordered-set-example" sequential="true">
<resource_ref id="A"/>
<resource_ref id="B"/>
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
</rsc_order>
</constraints>
While the set-based format is not less verbose, it is significantly easier to
get right and maintain.
.. important::
If you use a higher-level tool, pay attention to how it exposes this
functionality. Depending on the tool, creating a set **A B** may be equivalent to
**A then B**, or **B then A**.
Ordering Multiple Sets
______________________
The syntax can be expanded to allow sets of resources to be ordered relative to
each other, where the members of each individual set may be ordered or
unordered (controlled by the ``sequential`` property). In the example below, **A**
and **B** can both start in parallel, as can **C** and **D**, however **C** and
**D** can only start once *both* **A** *and* **B** are active.
.. topic:: Ordered sets of unordered resources
.. code-block:: xml
<constraints>
<rsc_order id="order-1">
<resource_set id="ordered-set-1" sequential="false">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
<resource_set id="ordered-set-2" sequential="false">
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
</rsc_order>
</constraints>
.. topic:: Visual representation of the start order for two ordered sets of
unordered resources
.. image:: images/two-sets.png
:alt: Two ordered sets
Of course either set -- or both sets -- of resources can also be internally
ordered (by setting ``sequential="true"``) and there is no limit to the number
of sets that can be specified.
.. topic:: Advanced use of set ordering - Three ordered sets, two of which are
internally unordered
.. code-block:: xml
<constraints>
<rsc_order id="order-1">
<resource_set id="ordered-set-1" sequential="false">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
<resource_set id="ordered-set-2" sequential="true">
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
<resource_set id="ordered-set-3" sequential="false">
<resource_ref id="E"/>
<resource_ref id="F"/>
</resource_set>
</rsc_order>
</constraints>
.. topic:: Visual representation of the start order for the three sets defined above
.. image:: images/three-sets.png
:alt: Three ordered sets
.. important::
An ordered set with ``sequential=false`` makes sense only if there is another
set in the constraint. Otherwise, the constraint has no effect.
Resource Set OR Logic
_____________________
The unordered set logic discussed so far has all been "AND" logic. To illustrate
this take the 3 resource set figure in the previous section. Those sets can be
expressed, **(A and B) then (C) then (D) then (E and F)**.
Say for example we want to change the first set, **(A and B)**, to use "OR" logic
so the sets look like this: **(A or B) then (C) then (D) then (E and F)**. This
functionality can be achieved through the use of the ``require-all`` option.
This option defaults to TRUE which is why the "AND" logic is used by default.
Setting ``require-all=false`` means only one resource in the set needs to be
started before continuing on to the next set.
.. topic:: Resource Set "OR" logic: Three ordered sets, where the first set is
internally unordered with "OR" logic
.. code-block:: xml
<constraints>
<rsc_order id="order-1">
<resource_set id="ordered-set-1" sequential="false" require-all="false">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
<resource_set id="ordered-set-2" sequential="true">
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
<resource_set id="ordered-set-3" sequential="false">
<resource_ref id="E"/>
<resource_ref id="F"/>
</resource_set>
</rsc_order>
</constraints>
.. important::
An ordered set with ``require-all=false`` makes sense only in conjunction with
``sequential=false``. Think of it like this: ``sequential=false`` modifies the set
to be an unordered set using "AND" logic by default, and adding
``require-all=false`` flips the unordered set's "AND" logic to "OR" logic.
.. _s-resource-sets-colocation:
Colocating Sets of Resources
############################
Another common situation is for an administrator to create a set of
colocated resources.
The simplest way to do this is to define a resource group (see
:ref:`group-resources`), but that cannot always accurately express the desired
relationships. For example, maybe the resources do not need to be ordered.
Another way would be to define each relationship as an individual constraint,
but that causes a difficult-to-follow constraint explosion as the number of
resources and combinations grow.
.. topic:: Colocation chain as individual constraints, where A is placed first,
then B, then C, then D
.. code-block:: xml
<constraints>
<rsc_colocation id="coloc-1" rsc="D" with-rsc="C" score="INFINITY"/>
<rsc_colocation id="coloc-2" rsc="C" with-rsc="B" score="INFINITY"/>
<rsc_colocation id="coloc-3" rsc="B" with-rsc="A" score="INFINITY"/>
</constraints>
To express complicated relationships with a simplified syntax [#]_,
:ref:`resource sets <s-resource-sets>` can be used within colocation constraints.
.. topic:: Equivalent colocation chain expressed using **resource_set**
.. code-block:: xml
<constraints>
<rsc_colocation id="coloc-1" score="INFINITY" >
<resource_set id="colocated-set-example" sequential="true">
<resource_ref id="A"/>
<resource_ref id="B"/>
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
</rsc_colocation>
</constraints>
.. note::
Within a ``resource_set``, the resources are listed in the order they are
*placed*, which is the reverse of the order in which they are *colocated*.
In the above example, resource **A** is placed before resource **B**, which is
the same as saying resource **B** is colocated with resource **A**.
As with individual constraints, a resource that can't be active prevents any
resource that must be colocated with it from being active. In both of the two
previous examples, if **B** is unable to run, then both **C** and by inference **D**
must remain stopped.
.. important::
If you use a higher-level tool, pay attention to how it exposes this
functionality. Depending on the tool, creating a set **A B** may be equivalent to
**A with B**, or **B with A**.
Resource sets can also be used to tell the cluster that entire *sets* of
resources must be colocated relative to each other, while the individual
members within any one set may or may not be colocated relative to each other
(determined by the set's ``sequential`` property).
In the following example, resources **B**, **C**, and **D** will each be colocated
with **A** (which will be placed first). **A** must be able to run in order for any
of the resources to run, but any of **B**, **C**, or **D** may be stopped without
affecting any of the others.
.. topic:: Using colocated sets to specify a shared dependency
.. code-block:: xml
<constraints>
<rsc_colocation id="coloc-1" score="INFINITY" >
<resource_set id="colocated-set-2" sequential="false">
<resource_ref id="B"/>
<resource_ref id="C"/>
<resource_ref id="D"/>
</resource_set>
<resource_set id="colocated-set-1" sequential="true">
<resource_ref id="A"/>
</resource_set>
</rsc_colocation>
</constraints>
.. note::
Pay close attention to the order in which resources and sets are listed.
While the members of any one sequential set are placed first to last (i.e., the
colocation dependency is last with first), multiple sets are placed last to
first (i.e. the colocation dependency is first with last).
.. important::
A colocated set with ``sequential="false"`` makes sense only if there is
another set in the constraint. Otherwise, the constraint has no effect.
There is no inherent limit to the number and size of the sets used.
The only thing that matters is that in order for any member of one set
in the constraint to be active, all members of sets listed after it must also
be active (and naturally on the same node); and if a set has ``sequential="true"``,
then in order for one member of that set to be active, all members listed
before it must also be active.
If desired, you can restrict the dependency to instances of promotable clone
resources that are in a specific role, using the set's ``role`` property.
.. topic:: Colocation in which the members of the middle set have no interdependencies,
and the last set listed applies only to instances in the master role
.. code-block:: xml
<constraints>
<rsc_colocation id="coloc-1" score="INFINITY" >
<resource_set id="colocated-set-1" sequential="true">
<resource_ref id="F"/>
<resource_ref id="G"/>
</resource_set>
<resource_set id="colocated-set-2" sequential="false">
<resource_ref id="C"/>
<resource_ref id="D"/>
<resource_ref id="E"/>
</resource_set>
<resource_set id="colocated-set-3" sequential="true" role="Master">
<resource_ref id="A"/>
<resource_ref id="B"/>
</resource_set>
</rsc_colocation>
</constraints>
.. topic:: Visual representation of the above example (resources are placed from
left to right)
.. image:: ../shared/images/pcmk-colocated-sets.png
:alt: Colocation chain
.. note::
Unlike ordered sets, colocated sets do not use the ``require-all`` option.
.. [#] While the human brain is sophisticated enough to read the constraint
in any order and choose the correct one depending on the situation,
the cluster is not quite so smart. Yet.
.. [#] which is not the same as saying easy to follow