Threshold alerts (plugin metrics, RTT) were firing immediately on the
first breach. Now every state transition to WARNING/CRITICAL starts a
grace-period timer (grace_seconds from the 'grace' config key). The
notification is deferred until the next heartbeat after grace_seconds
have elapsed. If the metric recovers within the grace window, both the
alert and the recovery are suppressed — no spurious pages for transient
spikes.
Two helper methods added to ThresholdChecker:
- _apply_grace: handles the state-change path (defer or suppress)
- _check_pending_or_renotify: handles the stable-alert path (fire
deferred notification once grace expires, or fall through to reminders)
The overdue case is unchanged — on_overdue already fires only after
interval+grace seconds of silence, which is equivalent behaviour.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
andreasandClaude Sonnet 4.6
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