Canary Release Feature Flag

Canary Release with Feature Flags

A canary release exposes a new feature to a very small percentage of production traffic (typically 1-5%) to detect issues before they affect all users. Named after the canary in a coal mine, this pattern provides early warning of problems.

Configuration Example

{
  "new-payment-gateway": {
    "name": "New Payment Gateway",
    "description": "Stripe integration replacing Braintree",
    "type": "boolean",
    "enabled": true,
    "defaultValue": false,
    "targeting": [
      {
        "type": "percentage-rollout",
        "percentage": 2
      }
    ]
  }
}

Canary vs Other Rollout Strategies

Strategy	Traffic	Purpose	Duration
Canary	1-5%	Detect bugs in production	Hours to 1 day
Beta	Segment-based	Gather feedback	Days to weeks
Gradual rollout	5% → 100%	Reduce risk	Days to weeks
Blue-green	0% or 100%	Zero-downtime deploy	Minutes

What to Monitor During Canary

Key Metrics for Canary Group vs Control:
├─ Error rate (HTTP 5xx)
├─ Latency (p50, p95, p99)
├─ CPU and memory usage
├─ Business metrics (conversion, revenue)
├─ Client-side errors (JavaScript exceptions)
└─ User complaints / support tickets

Automatic Canary Analysis

Some teams automate the canary decision:

1. Deploy canary at 2% traffic
2. Automated system compares canary metrics vs control for 1 hour
3. If metrics are within acceptable thresholds: auto-promote to 10%
4. If metrics degrade: auto-rollback to 0%
5. Continue promoting through stages until 100%

Canary Configuration for Multiple Metrics

{
  "canary-analysis-config": {
    "type": "json",
    "defaultValue": {
      "analysisInterval": "10m",
      "maxErrorRateIncrease": 0.5,
      "maxLatencyP99Increase": 100,
      "minimumSampleSize": 1000,
      "promotionSchedule": [2, 10, 25, 50, 100]
    }
  }
}

Rollback Criteria

Immediately rollback if:

• Error rate increases by more than 0.5% compared to control
• p99 latency increases by more than 100ms
• Any SEV-1 alerts fire for the canary group
• Revenue per user drops by more than 2%