ClusterLabs FAQ

Updated 346 Days AgoPublic

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Who can edit this wiki?

Anyone in the Developers group can edit this wiki. If you are not in the group but would like editing privileges, please email webmaster@clusterlabs.org.

Why was Pacemaker started?

Pacemaker grew out of the Heartbeat project. See the Pacemaker Project History for more details.

How did Pacemaker get its name?

First of all, it's not called the CRM (for Cluster Resource Manager) because of the abundance of terms that are commonly abbreviated to those three letters.

The Pacemaker name came from Kham, a good friend of Pacemaker author Andrew Beekhof's, and was originally used by a Java GUI Beekhof was prototyping in early 2007. The GUI was abandoned, and when it came time to choose a name for this project, Lars suggested it was an even better fit for an independent CRM.

The idea stems from the analogy between the role of this software and that of the little device that keeps the human heart pumping. Pacemaker monitors the cluster and intervenes when necessary to ensure the smooth operation of the services it provides.

What is Pacemaker's relationship with Corosync?

Pacemaker keeps your applications running when they or the machines they're running on fail. However, it can't do this without connectivity to the other machines in the cluster -- a significant problem in its own right.

Corosync provides a mechanism to reliably send messages between nodes, notifications when nodes join and leave the cluster, and a list of active nodes that is consistent throughout the cluster.

Is there any Pacemaker documentation?

Yes, see the Pacemaker documentation set.

Where should I ask questions?

Basic questions can often be answered on the ClusterLabs IRC Channel, but sending them to one of the relevant ClusterLabs Mailing Lists is always a good idea so that everyone can benefit from the answer.

Do I need shared storage?

No. We can help manage it if you have some, but Pacemaker itself has no need for shared storage.

Which cluster filesystems does ClusterLabs support?

ClusterLabs provides resource agents that support the popular OCFS2 and GFS2 filesystems. As you'd expect, you can use them on top of real disks or network block devices like DRBD.

What kind of applications can I manage with Pacemaker?

Pacemaker is application-agnostic, able to start, stop, monitor, and otherwise interact with applications via supported standards:

• Systemd unit files
• LSB init scripts
• Open Cluster Framework (OCF) resource agents

(Before version 3.0.0, Pacemaker also supported the Upstart and Nagios standards.)

For details, see "Resource Classes" in the Pacemaker Explained document.

Do I need a fencing device?

Yes. Fencing is the only 100% reliable way to ensure the integrity of your data and that applications are only active on one host. Although Pacemaker is able to function without fencing, there are good reasons vendors will not support such a configuration.

Do I need to know XML to configure Pacemaker?

No. Pacemaker uses XML as its native configuration format, but command-line and graphical user interfaces are available for human-friendly management.

How do I synchronize the cluster configuration?

Any changes to Pacemaker's configuration are automatically replicated to other machines. The configuration is also versioned, so any offline machines will be updated when they return.

Should I choose pcs or crm shell?

Arguably the best advice is to use whichever one comes with your distro. This is the one that will be tailored to that environment, receive regular bugfixes and feature in the documentation.

Of course, for years people have been side-loading all of Pacemaker onto enterprise distros that didn't ship it, so doing the same for just a configuration tool should be easy if your favorite distro does not ship your favorite tool.

What if my question isn't here?

See our help page and let us know!

What versions of Pacemaker are supported?

When seeking assistance, please try to ensure you have a version still actively developed. See the Pacemaker Release Calendar for details.

Technical

How do I install Pacemaker?

See How To Install.

Can I use Pacemaker with Corosync 2.x and later?

Yes. This is the only option supported in Pacemaker 2.0.0 and later. See "Cluster Architecture" in the Clusters from Scratch document for details.

Can I use Pacemaker with Heartbeat?

Only with Pacemaker versions less than 2.0.0. See Linux-HA documentation for details.

Can I use Pacemaker with CMAN?

Only with Pacemaker versions greater than or equal to 1.1.5 and less than 2.0.0. See the documentation for details.

Can I use Pacemaker with Corosync 1.x?

Only with Pacemaker versions less than 2.0.0. You will need to configure Corosync to load Pacemaker's custom plugin. See the documentation for details.

Can I mix different cluster layers in the same cluster?

No.

Where can I get the source code?

• The source code can be browsed at GitHub or downloaded as a tarball.

• Alternatively, you can get a full copy of the Git repository by executing git clone git://github.com/ClusterLabs/pacemaker.git

Where can I get pre-built packages?

Most users should be able to install Pacemaker directly from their distribution.

Pacemaker currently ships with Fedora (since 12), RedHat Enterprise Linux (since 6.0), openSUSE (since 11.0), Debian (since "Squeeze"), Ubuntu LTS (since 10.4 "Lucid Lynx”) and as a key component of the High Availability Extension for SUSE Linux Enterprise Server (since 11).

Users of other distributions should refer to How To Install.

How do I test my Cluster?

Pacemaker comes with a Cluster Test Suite (CTS for short) which is an integral part of our release testing. See the CTS README for details.

What are multiply active resources?

Pacemaker will try to determine what resources are active on a node when it joins the cluster. To do this, it sends what we call a probe, using resource agents' monitor operation. There are two common reasons for seeing a log message about a resource being multiply active:

• Your resource really is active on more than one node
  • Ensure the service is not enabled to start at system boot
  • Ensure administrators do not start the service manually anywhere
  • Did Pacemaker suffer an internal failure? If so, please see Getting Help and report it
• Your resource agent doesn't implement the monitor operation correctly
  • Make sure your resource agent conforms to the OCF standard by using the ocf-tester script

You may also want to read the documentation for the multiple-active option which controls what Pacemaker does when it encounters this condition.

I killed a node but the cluster didn't recover

One of the most common reasons for this is the way quorum is calculated for a 2-node cluster. Corosync 2 doesn't pretend 2-node clusters always have quorum. (Corosync 3 has the two-node option to select the desired behavior.)

In order to have quorum, more than half of the total number of cluster nodes need to be online. Clearly this is not the case when a node failure occurs in a 2-node cluster.

If you want to allow the remaining node to provide all the cluster services, you need to set the no-quorum-policy to ignore.

crm configure property no-quorum-policy=ignore

Just be sure to set up fencing to ensure data integrity.

Features

Colocation Sets

The sequential option does not refer to ordering. Instead it tells Pacemaker to create a colocation chain between the members of the set. For example:

colocation myset inf: app1 app2 app3 app4

is the equivalent of

colocation myset-1 inf: app2 app1
colocation myset-2 inf: app3 app2
colocation myset-3 inf: app4 app3

(app4 -> app3 -> app2 -> app1)

Putting them in brackets sets sequential=false and removes the internal constraints. So:

colocation myset inf: app1 ( app2 app3 app4 )

is actually the equivalent of

colocation myset-1 inf: app2 app1
colocation myset-2 inf: app3 app1
colocation myset-3 inf: app4 app1

(app2 -> app1, app3 -> app1, app4 -> app1)

The difference has implications when there is a failure. With sequential turned on, a failure in app2 results in app3 and app4 also being restarted. However with sequential turned off, a failure in app2 does not affect app3 or app4. In both cases, a failure in app1 results in all resources being restarted.