What Is Blue-Green & Canary Deployment? Zero Downtime Guide

Does every deployment give you a heart attack? Can you roll back instantly? Blue-Green and Canary Deployment deliver zero-downtime, safe releases.

1. Blue-Green Deployment

Two identical environments. Traffic switches instantly.

Before:  LB → [Blue v1.0] ← all traffic
After:   LB → [Green v2.0] ← all traffic
Rollback: LB → [Blue v1.0] ← instant switch back

✅ Zero downtime | ✅ Instant rollback | ❌ Double resource cost

2. Canary Deployment

Gradually roll out to a small percentage of users, then increase.

Phase 1:  5% → v2.0  | 95% → v1.0
Phase 2: 25% → v2.0  | 75% → v1.0
Phase 3: 100% → v2.0 → Full rollout ✅

✅ Gradual risk | ✅ Real user validation | ❌ Complex infrastructure

Istio Canary

http:
  - route:
      - destination: { host: app, subset: stable }
        weight: 95
      - destination: { host: app, subset: canary }
        weight: 5

3. Rolling Update

Update pods one at a time (Kubernetes default).

Comparison

| Strategy | Downtime | Rollback | Risk | Cost | |----------|----------|----------|------|------| | Recreate | Yes | Slow | High | Low | | Rolling | No | Medium | Medium | Low | | Blue-Green | No | Instant | Low | High | | Canary | No | Fast | Lowest | Medium |

Database Migrations

Use the Expand-Migrate-Contract pattern for backward-compatible schema changes.

Best Practices

1. Combine with feature flags — Deployment ≠ release
2. Health checks required — Auto-rollback unhealthy pods
3. Automatic rollback — Set error rate thresholds
4. DB backward compatibility — Deploy schema changes separately
5. Smoke tests — Automated post-deploy verification

Conclusion

Zero-downtime deployment is the modern standard. Blue-Green provides instant switching, Canary manages risk gradually. Choose based on your team's needs.

Learn deployment strategies on LabLudus.