Chapter 6. Clustering

Pacemaker now supports alert agents

You can now create Pacemaker alert agents to take some external action when a cluster event occurs. The cluster passes information about the event to the agent by means of environment variables. Agents can do anything desired with this information, such as send an email message, log to a file, or update a monitoring system. For information on configuring alert agents, see the Red Hat Enterprise Linux 7 High Availability Add-On Reference: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/High_Availability_Add-On_Reference/index.html. (BZ#1315371)

Pacemaker now supports SBD fencing configuration

The SBD daemon integrates with Pacemaker, a watchdog device, to arrange for nodes to reliably self-terminate when fencing is required. This update adds the pcs stonith sbd command to configure SBD in Pacemaker, and it is now also possible to configure SBD from the web UI. SBD fencing can be particularly useful in environments where traditional fencing mechanisms are not possible. For information on using SBD with Pacemaker, see the following Red Hat Knowledgebase article: https://access.redhat.com/articles/2212861. (BZ#1164402)

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#1288929)

A Pacemaker cluster resource that is used to create a guest node may now be a member of a resource group

Previous Pacemaker versions did not support including a guest node in a group. As of Red Hat Enterprise Linux 7.3, a Pacemaker cluster resource such as VirtualDomain that is used to create a guest node may now be a member of a resource group. This can be useful, for example, to associate a virtual machine with its storage. (BZ#1303765)

pcsd now supports setting SSL options and ciphers

Previously, the pcsd service did not enable the user to easily disable a cipher or a particular version of the SSL or TSL protocol if a vulnerability was found of if the protocol version or the cipher was considered weak for some reason. With this update, the user can easily configure SSL options and ciphers in pcsd, and RC4 ciphers as well as TLS protocol version 1.1 and earlier are disabled by default. (BZ#1315652)

pcs now supports setting expected votes on a live cluster

When nodes fail in a cluster, user sometimes needs to manually lower expected votes in order to recover the cluster. You can now use the pcs quorum expected-votes command to set expected votes on a live cluster. (BZ#1327739)

Support added for configuring Pacemaker utilization attributes

You can now configure Pacemaker utilization attributes with the pcs command and the pcsd Web UI. This allows you to configure the capacity a particular node provides, the capacity a particular resource requires, and an overall strategy for placement of resources. For information on utilization and placement strategy, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/High_Availability_Add-On_Reference/index.html. (BZ#1158500)