Most anomaly discussions start with spikes: sudden login failures, unusual API volume, or geographic jumps. Silence can be just as informative. If nightly batch jobs normally emit completion events and then stop, something changed — whether a broken pipeline, a suppressed logger, or intentional tampering.
Treat expected cadence as a first-class signal. Document which applications produce heartbeat-style security or audit events, and at what rhythm. When those messages vanish for longer than a defined grace window, raise a missing-event anomaly rather than waiting for a user complaint.
Be careful with holidays and maintenance windows. Ulsan and Seoul teams often schedule releases on weekends; without a calendar of planned quiet periods, silence detectors cry wolf. Pair missing-event rules with change tickets or release notes when possible.
During investigations, compare the last successful event’s contents with nearby systems. Did the load balancer still see traffic? Did the database still receive writes? Divergence between layers often pinpoints whether logging failed or the application itself stalled.