Alarms and Automated Actions

~8 min read

How an alarm decides when to fire, and what it can actually do about it.

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Key points

  • Alarms evaluate a metric against a threshold over a defined evaluation period, typically requiring multiple consecutive breaches
  • Actions include SNS notification, Auto Scaling triggers, and EC2 recovery actions — the same mechanism for both human alerts and automation
  • Composite alarms combine multiple alarms with AND/OR logic to reduce noise from related conditions
  • Well-tuned thresholds come from actual historical metric behavior, not arbitrary guesses