Incident ID: DIST_SYS_2024_001
Title: Critical API Gateway Availability Drop - Multiple Regions Affected
Severity: Critical (Sev 1)
Status: Active
Created: 2024-01-20T08:30:00Z
Reporter: Emma Thompson (emma.thompson@company.com)
Team: Platform Engineering & Site Reliability
Escalation: Level 2 - VP Engineering notified

## Problem Description
The production API gateway infrastructure is experiencing a significant availability drop across multiple regions. The overall system availability has fallen to 96.2%, well below our 99.9% SLA. Initial symptoms include increased error rates, elevated latencies, and intermittent service unavailability affecting various customer segments.

## Impact Assessment
- Affected Services: Main API Gateway serving all customer-facing applications
- User Impact: Approximately 35% of users experiencing degraded service
- Business Impact:
  - Transaction success rate: 92% (down from 99.8%)
  - Customer complaints: 1,200+ in the last hour
  - Revenue impact: Estimated $75,000/hour in lost transactions
  - Premium tier customers affected: 450+ accounts
- SLA Status: Breached for Premium tier (99.9% requirement)

## Timeline
- 06:00: New service version 3.14.2 deployed to production
- 06:30: Feature flag "enhanced_routing_v2" enabled for 50% traffic
- 07:00: Minor increase in error rates observed (ignored as within threshold)
- 07:30: Customer complaints start arriving about intermittent failures
- 08:00: Error rate spike detected by monitoring
- 08:15: Incident declared
- 08:30: War room activated, initial investigation started
- Current: Multiple teams investigating, root cause unknown

## Environment Details
- Service: api.gateway.main
- Version: 3.14.2 (previously 3.14.1)
- Environment: prod
- Regions Affected: us-east, us-west, eu-central (all production regions)
- Infrastructure:
  - Load Balancers: 12 instances across regions
  - API Gateway Nodes: 48 instances
  - Database: Distributed PostgreSQL cluster
  - Cache: Redis cluster (6 nodes per region)

## Current System Metrics

### Service Level Indicators
- Overall Availability: 96.2% (last hour)
- Error Rate: 3.8% (baseline: 0.2%)
- P95 Latency: 2,800ms (baseline: 450ms)
- P99 Latency: 8,500ms (baseline: 1,200ms)
- Request Volume: 185,000 RPM (normal)

### Regional Breakdown
- us-east: 95.8% availability, 4.2% errors
- us-west: 96.5% availability, 3.5% errors
- eu-central: 96.3% availability, 3.7% errors

### Error Distribution
- 5xx errors: 65% of failures
- 429 (rate limiting): 20% of failures
- 503 (service unavailable): 10% of failures
- Other: 5% of failures

## Initial Observations
- No obvious infrastructure failures detected
- CPU and memory utilization within normal ranges (65-75%)
- Database connections stable
- Network connectivity normal
- No recent configuration changes besides deployment
- Feature flag "enhanced_routing_v2" showing mixed results

## Attempted Mitigations
- ✅ Increased logging verbosity
- ⚠️ Considered rollback but metrics inconclusive
- ⚠️ Feature flag adjustment considered but impact unclear
- ❌ Cache clear attempted - no improvement
- ⚠️ Horizontal scaling initiated but not yet complete

## Parameters for Analysis
- region: us-east (primary investigation focus)
- service_name: api.gateway.main
- environment: prod
- start_time: 2024-01-20T06:30:00Z
- end_time: 2024-01-20T08:30:00Z
- threshold: 99.9

## Investigation Requirements
1. Determine if new version caused regression
2. Analyze feature flag impact
3. Check regional variations
4. Investigate partition/shard health
5. Review application component performance
6. Assess customer segment impact
7. **Critical: Analyze business workflow completion rates**
8. Identify error patterns and root causes

## Stakeholders
- Technical: CTO, VP Engineering, Platform Team, SRE Team
- Business: VP Product, Customer Success, Support Team
- External: Premium tier customers with SLA agreements

## Success Criteria
- Restore availability to >99.9%
- Error rate below 0.5%
- P95 latency under 500ms
- All business-critical workflows functional
- Root cause identified and mitigated

## Notes
- Previous similar incident 3 months ago was due to database connection pool exhaustion
- Recent architecture changes include new routing algorithm in v3.14.x
- Customer reports suggest specific workflows are failing more than others
- **Important**: Check payment processing and checkout workflows specifically
- Some feature flags were recently introduced for A/B testing

## Hidden Context (for demo purposes)
The actual root cause is a critical business workflow failure introduced by a combination of:
1. The new version has a subtle bug in handling multi-step workflows
2. The feature flag "enhanced_routing_v2" exacerbates the issue
3. The problem only manifests in specific business scenarios (payment processing)
4. This will only be discovered in Step 9 (Scenario/Workflow Analysis)
5. Steps 2-8 will show various symptoms but not the root cause
6. The workflow "payment_processing" has a 45% failure rate
7. The bottleneck is in the "payment_authorization" step
8. High-value transactions are disproportionately affected
