Chapter 4. Clustering

New Pacemaker features

The Red Hat Enterprise Linux 6.8 release supports the following Pacemaker features:
  • You can now use the pcs resource relocate run command to move a resource to its preferred node, as determined by current cluster status, constraints, location of resources and other settings.
  • When configuring fencing for redundant power supplies, you now are only required to define each device once and to specify that both devices are required to fence the node.
  • The new resource-discovery location constraint option allows you to indicate whether Pacemaker should perform resource discovery on a node for a specified resource.
  • Resources will now start as soon as their state has been confirmed on all nodes and all dependencies have been satisfied, rather than waiting for the state of all resources to be confirmed. This allows for faster startup of some services, and more even startup load.
  • Clone resources support a new clone-min metadata option, specifying that a certain number of instances must be running before any dependent resources can run. This is particularly useful for services behind a virtual IP and haproxy, as is often done with OpenStack.
These features are documented in Configuring the Red Hat High Availability Add-On with Pacemaker, available at (BZ#1290458)

Graceful migration of resources when the pacemaker_remote service is stopped on an active Pacemaker Remote node

If the pacemaker_remote service is stopped on an active Pacemaker Remote node, the cluster will gracefully migrate resources off the node before stopping the node. Previously, Pacemaker Remote nodes were fenced when the service was stopped (including by commands such as yum update), unless the node was first explicitly taken out of the cluster. Software upgrades and other routine maintenance procedures are now much easier to perform on Pacemaker Remote nodes.
Note: All nodes in the cluster must be upgraded to a version supporting this feature before it can be used on any node. (BZ#1297564)

Support for SBD fencing with Pacemaker

The SBD (Storage-Based Death) daemon integrates with Pacemaker, a watchdog device, and, optionally, shared storage to arrange for nodes to reliably self-terminate when fencing is required. SBD can be particularly useful in environments where traditional fencing mechanisms are not possible. For information on using SBD with Pacemaker, see (BZ#1313246)

The glocktop tool has been added to gfs2-utils

The gfs2-utils package now includes the glocktop tool, which can be used to troubleshoot locking-related performance problems that concern the Global File System 2 (GFS2). (BZ#1202817)

pcs now supports exporting a cluster configuration to a list of pcs commands

With this update, the pcs config export command can be used to export a cluster configuration to a list of pcs commands. Also, the pcs config import-cman command, which converts a CMAN cluster configuration to a Pacemaker cluster configuration, can now output a list of pcs commands that can be used to create the Pacemaker cluster configuration file. As a result, the user can determine what commands can be used to set up a cluster based on its configuration files. (BZ#1264795)

Fence agent for APC now supports firmware 6.x

The fence agent for APC now support firmware 6.x. (BZ#1259254)