About inter-system cluster communications

VCS uses the cluster interconnect for network communications between cluster systems. Each system runs as an independent unit and shares information at the cluster level. On each system the VCS High Availability Daemon (HAD), which has the decision logic for the cluster, maintains a view of the cluster configuration. This daemon operates as a replicated state machine, which means all systems in the cluster have a synchronized state of the cluster configuration. This is accomplished by the following:

The replicated state machine communicates over a purpose-built communications package consisting of two components, Group Membership Services/Atomic Broadcast (GAB) and Low Latency Transport (LLT).

See About Group Membership Services/Atomic Broadcast (GAB).

See About Low Latency Transport (LLT).

Figure: Cluster communications with replicated state machine illustrates the overall communications paths between two systems of the replicated state machine model.

Figure: Cluster communications with replicated state machine

Cluster communications with replicated state machine