Documentation

The mirror worker's consume-loop heartbeat: the wall-clock time of the worker's last successful poll of the queue.

It is the worker's own liveness signal, kept apart from the server's HTTP readiness so single-process health reflects a stalled worker today and a future standalone worker binary keeps the same probe. The worker recordPolls after each successful receive (whether or not the batch was empty -- an empty long-poll is a healthy idle, not a stall); a liveness probe reads lastPoll and compares it against the wall clock to decide whether the loop has gone quiet for too long.

Build a fresh WorkerHeartbeat with no poll yet recorded (lastPoll is Nothing until the worker's first successful receive).

Record the time of a successful queue poll, advancing the heartbeat. Called by the worker after each receive returns (the loop is alive even on an empty batch).

The time of the worker's last successful poll, or Nothing before its first. A liveness probe reads this and compares it against the wall clock.

How long the worker's last successful poll may be stale before the loop is considered stalled -- the staleness threshold the liveness probe applies.

It is a generous multiple of the long-poll cadence: a healthy idle worker still completes a poll at least every sqsWaitSeconds (≤ 20s by default), so a gap several times that is a genuine stall, not an idle queue. Set well above one poll window so liveness never flaps on normal scheduling jitter.

Whether the worker's consume loop is healthy as of now, given its last successful poll. This is the liveness signal the single-process /livez probe folds in (see Ecluse.Server), distinct from HTTP readiness.

• Nothing (no poll yet) is healthy: the worker is still starting, not stalled.
• A poll within workerHeartbeatStaleAfter is healthy.
• A poll older than that is unhealthy: the loop has gone quiet for too long.

>>> import Data.Time (UTCTime (UTCTime), fromGregorian, secondsToDiffTime)
>>> let t0 = UTCTime (fromGregorian 2020 1 1) (secondsToDiffTime 0)
>>> heartbeatHealthy t0 Nothing
True

>>> let now = UTCTime (fromGregorian 2020 1 1) (secondsToDiffTime 10)
>>> heartbeatHealthy now (Just t0)
True

>>> let later = UTCTime (fromGregorian 2020 1 1) (secondsToDiffTime 300)
>>> heartbeatHealthy later (Just t0)
False

Read the worker heartbeat and decide liveness against the current wall clock -- the IO wrapper the liveness probe calls. True while the consume loop is alive (or still starting); False once the last successful poll is staler than workerHeartbeatStaleAfter.