Peer domain on Cluster Aware AIX

Cluster Aware AIX® (CAA) introduces fundamental clustering capability to AIX, including definition of the set of nodes that comprise the cluster, and detection of node and interface liveness.

When RSCT operates on nodes in a CAA cluster, a peer domain is created that is equivalent to and represents the CAA cluster, and can be used to manage the cluster by using peer domain commands and interfaces. This peer domain presents largely the same set of function to users and software as other peer domains not based on CAA. But where a peer domain, which is operating without CAA, autonomously manages and monitors the configuration and liveness of the nodes and interfaces that it comprises, the peer domain that represents a CAA cluster acquires configuration information and liveness results from CAA. It introduces some differences in the mechanics of peer domain operations, but very few in the view of the peer domain that is exposed to the users.

Only one CAA cluster can be defined on a set of nodes. Therefore, if a CAA cluster is defined then the peer domain that represents it is the only peer domain which can exist, and it exists and be online for the life of the CAA cluster. If no CAA cluster is configured, then existing and new peer domains that operate in the autonomous mode can be used with no change in function. CAA function is only available on AIX, and on all other supported platforms, peer domain function operating in the autonomous mode is unchanged.

A CAA cluster and the equivalent RSCT peer domain operate hand in hand such that a change made to the CAA cluster by using CAA commands and interfaces, is reflected automatically in the corresponding peer domain; similarly the existing peer domain commands applied to a peer domain operating on CAA result in equivalent changes to the CAA cluster. So, for example, when you create a CAA cluster by using mkcluster command, the equivalent peer domain also gets created as a result, while the mkrpdomain command can be used to create a peer domain and the underlying CAA cluster in one operation. Similarly node add and delete operations that use either peer domain or cluster commands are applied to both the CAA cluster and the peer domain.

Because a peer domain operating on CAA exists and is online for the life of the CAA cluster, some operations that are relevant to peer domains not operating on CAA, startrpdomain, stoprpdomain, startrpnode, and stoprpnode, have no effect on a peer domain that is running on a CAA cluster. Also, the preprpnode command, which is used to exchange public keys among nodes in preparation for peer domain creation, is not needed when a peer domain based on a CAA cluster is to be created.

In a peer domain that represents a CAA cluster, the definition of quorum might change depending on the installed AIX release.

RSCT version 3.1.2.0, or later, can be installed on the nodes and can coexist with prior RSCT releases. Until RSCT is upgraded to at least version 3.1.2.0 on all of the cluster nodes, the quorum is determined by the ability of the group leader node of the configuration resource manager to connect to the CAA services and acquire configuration information. If the group leader node loses this ability, it releases the group leader role to some other node in the cluster.

After the RSCT level is upgraded to version 3.1.2.0, or later, on all of the cluster nodes and for all domains that represent CAA clusters on AIX 6.1 with Technology Level 7, AIX 7.1 with Technology Level 1, or AIX 7.2 quorum is determined by the value of the QuorumType attribute of the IBM®.PeerNode resource class.

For all of the RSCT release levels on CAA clusters, peer domain operations can be used to change the configuration of the peer domain and the CAA cluster. CAA services provide RSCT with the authorized view of the cluster node configuration and activities. The quorum definition that it uses determines when configuration can be changed by using RSCT operations. The changes can affect either global resource configuration that is specific to RSCT or CAA cluster configuration.