Incident Response Team • Post-Incident Report
Automated monitoring alerted on elevated p95 latency in US-East cluster. Initial investigation showed database connection pool exhaustion.
EU-West cluster began exhibiting similar symptoms. Customer reports increased. Incident declared and response team mobilized.
Connection pool limits increased and read replicas scaled. Traffic throttled to 80% capacity. Error rates began declining.
All metrics returned to baseline. Root cause identified in database migration script. Monitoring elevated for 24 hours.
A database schema migration deployed at 09:38 UTC introduced a slow query on the sessions table. The new index was not properly backfilled, causing full table scans on every session lookup request.
Combined with a concurrent 3x traffic spike from a new enterprise customer onboarding, the database connection pools in both regions saturated within minutes. Our auto-scaling reacted but took 15 minutes to provision additional read replicas.
Contributing factors: Migration lacked a canary deployment phase; backfill job was not monitored; auto-scaling cooldown period was too aggressive.
Immediate: Rolled back problematic migration and implemented proper index backfill before re-deployment
This week: Updated database migration pipeline to require blue-green deployment approval for schema changes
This month: Reduced auto-scaling cooldown from 10 to 3 minutes; added pre-warmed capacity buffer
Ongoing: Implemented query performance monitoring alerts; added migration dry-run validation to CI/CD