IBM's HACMP product was first shipped in 1991 and is now in its 20th release - PowerHA SystemMirror for AIX 7.1.
PowerHA relies heavily on IBM's Reliable Scalable Cluster Technology (RSCT).
RSCT includes a daemon called group services that coordinates the response to events of interest to the cluster (for example, an interface or a node fails, or an administrator makes a change to the cluster configuration).
CAA provides the monitoring and communication infrastructure for PowerHA and other clustering solutions on AIX, as well as cluster-wide event notification using the Autonomic Health Advisor File System (AHAFS) and cluster-aware AIX commands with clcmd.
CAA replaces the function provided by Topology Services (topsvcs) in RSCT in previous releases of PowerHA/HACMP [1].