Postmortem Writer
Document incidents for learning and improvement.
Postmortem Template
# Postmortem: API Outage - Database Connection Pool Exhausted
**Date:** 2024-01-15
**Authors:** Jane Doe (On-call), John Smith (DBA)
**Status:** Complete
**Severity:** P1 (Critical)
## Summary
On January 15, 2024, our API experienced a complete outage for 25 minutes (14:32 - 14:57 UTC) affecting 100% of users. The root cause was database connection pool exhaustion triggered by a connection leak introduced in deployment v2.3.4.
**Impact:**
- Duration: 25 minutes
- Users affected: ~50,000
- Requests failed: ~125,000
- Revenue impact: ~$15,000
## Timeline (All times UTC)
| Time | Event |
| ----- | ------------------------------------------------ |
| 14:15 | v2.3.4 deployed to production |
| 14:32 | First CloudWatch alarm: HighErrorRate |
| 14:33 | PagerDuty alert sent to on-call (Jane) |
| 14:35 | Jane acknowledges, begins investigation |
| 14:38 | Identified: Database connection pool at 100% |
| 14:40 | Attempted: Kill long-running queries (no effect) |
| 14:43 | Decision: Rollback to v2.3.3 |
| 14:45 | Rollback initiated |
| 14:47 | Rollback complete, connections dropping |
| 14:50 | Error rate returning to normal |
| 14:57 | All systems recovered, incident closed |
| 15:30 | Postmortem meeting scheduled |
## Root Cause
A code change in v2.3.4 introduced a connection leak in the user profile endpoint. The new caching layer was not properly releasing database connections after queries completed.
**Code diff:**
\`\`\`diff
- await prisma.user.findUnique({ where: { id } });
* const client = await pool.connect();
* const user = await client.query('SELECT \* FROM users WHERE id = $1', [id]);
* // Missing: client.release() ❌
\`\`\`
## Contributing Factors
1. **Insufficient testing:** Load tests didn't catch the leak
- Tests only ran for 5 minutes
- Not enough concurrent connections to exhaust pool
2. **Missing monitoring:** No alerts on connection pool metrics
- Had alarms for query latency
- No alarms for active connections count
3. **Inadequate code review:** Reviewer didn't spot missing release()
- PR approved without running locally
- No checklist for connection management
4. **Deployment process:** No gradual rollout
- Deployed to 100% of production immediately
- No canary deployment
## What Went Well
1. ✅ **Fast detection:** Alert fired within 3 minutes
2. ✅ **Clear runbook:** DBA runbook had exact steps to follow
3. ✅ **Quick decision:** Made rollback decision in 8 minutes
4. ✅ **Communication:** Status page updated every 5 minutes
5. ✅ **Rollback capability:** Automated rollback took <2 minutes
## What Went Wrong
1. ❌ **Code review missed bug:** Connection leak not caught
2. ❌ **Testing gaps:** Load tests insufficient duration
3. ❌ **No canary:** Deployed to all instances at once
4. ❌ **Late detection:** 17 minutes between deploy and alert
## Action Items
| Action | Owner | Due Date | Priority | Status |
| --------------------------------------------- | ------- | ---------- | -------- | -------------- |
| Add connection pool metrics to dashboards | Jane | 2024-01-20 | P0 | ✅ Done |
| Create PR checklist for connection management | John | 2024-01-22 | P0 | ✅ Done |
| Extend load tests to 30 minutes minimum | QA Team | 2024-01-25 | P1 | 🔄 In Progress |
| Implement canary deployment (10% → 100%) | DevOps | 2024-02-01 | P1 | 📋 Planned |
| Add connection leak detection to tests | Jane | 2024-01-27 | P1 | 🔄 In Progress |
| Review all DB connection usage patterns | John | 2024-02-05 | P2 | 📋 Planned |
| Improve alert routing (faster escalation) | DevOps | 2024-02-10 | P2 | 📋 Planned |
## Lessons Learned
1. **Code review checklists work:** Need specific items for common issues
2. **Load tests need realistic duration:** 5min insufficient for leaks
3. **Gradual rollouts catch issues:** 10% canary would have limited impact
4. **Monitoring gaps are dangerous:** Add metrics before you need them
5. **Runbooks save time:** Clear procedures enabled fast response
## Related Incidents
- [2023-11-20] Database CPU spike (similar connection pool issue)
- [2023-08-15] Memory leak in cache layer
## Prevention
To prevent similar incidents:
1. ✅ Add connection management to code review checklist
2. ✅ Monitor connection pool utilization
3. ✅ Extend load test duration
4. ✅ Implement canary deployments
5. ✅ Add automated connection leak detection
## Appendix
### Monitoring Graphs
[Insert graphs of connection pool, error rates, latency during incident]
### Communication Log
[Insert status page updates and customer communication]
### Code Fix
PR #1235: Fix connection leak in user profile endpoint
\`\`\`typescript
const client = await pool.connect();
try {
const user = await client.query('SELECT \* FROM users WHERE id = $1', [id]);
return user;
} finally {
client.release(); // ✅ Always release
}
\`\`\`
Postmortem Best Practices
# Blameless Postmortem Guidelines
## Do ✅
- Focus on systems and processes, not people
- Use timeline with exact timestamps
- Identify contributing factors, not just root cause
- Create actionable items with owners and dates
- Document what went well (positive reinforcement)
- Share widely for organizational learning
## Don't ❌
- Blame individuals or teams
- Hide or minimize the incident
- Skip the postmortem (even for small incidents)
- Create action items without owners
- Forget to follow up on action items
- Make it a blame session
## Template Sections
1. **Summary** (2-3 sentences)
2. **Impact** (numbers: users, revenue, duration)
3. **Timeline** (chronological events)
4. **Root Cause** (technical explanation)
5. **Contributing Factors** (broader context)
6. **What Went Well** (positive reinforcement)
7. **What Went Wrong** (improvement areas)
8. **Action Items** (concrete, owned, dated)
9. **Lessons Learned** (key takeaways)
Output Checklist
- Timeline created
- Root cause identified
- Contributing factors documented
- Action items with owners
- Lessons learned captured
- Postmortem meeting held
- Document shared widely
- Follow-up scheduled ENDFILE
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