Check Cluster Health

Required role: read or higher.

Determine the latest cluster health via the latest cluster monitor event. Each service's unchanged_since reports the approximate time it last transitioned between healthy and unhealthy, bounded by event retention.

The cluster monitor is the only writer of these events. In the enterprise edition it runs within the runner process, so when the runner dies the newest event keeps describing a cluster that no longer exists; elsewhere the monitor is a task in the process that answers this request. Either way a service cannot report its own death, so this endpoint additionally checks how old that event is. A stale response repeats the last recorded statuses instead of describing the cluster now, and counts as unhealthy: monitoring that has died cannot vouch for anything.