What is the name of the High Availability agent log?

Starting with vSphere 5.0, VMware replaced the legacy AAM agent with the Fault Domain Manager (FDM) as the High Availability agent; FDM writes its log to /var/log/fdm.log on each ESXi host, making fdm.log the authoritative log file for diagnosing HA agent behavior, master/slave elections, and failover activity.

ha.log is not a standard VMware vSphere log file; no HA-specific log by that name exists in the ESXi file system.

vpxa.log is the log for the vCenter Server agent (vpxa) running on ESXi hosts that manages vCenter communication, and is unrelated to the HA agent.

aam.log was associated with the legacy Automated Availability Manager (AAM) HA agent used in pre-vSphere 5.0 versions; it was superseded by fdm.log when FDM replaced AAM.