Zero-downtime deployments

Why deployment must not be an event¶

If your team has a “deployment window” and everyone is on standby, the system is telling you something important: the deployment process is broken. Deployment should be routine — like a commit, like code review. Automated, tested, with a clear rollback plan.

Blue-Green Deployment¶

Two identical environments:

1. Blue — current production, serving 100% of traffic
2. Green — new version, deployed and tested
3. Smoke tests on green ✅ → traffic switch (DNS or load balancer)
4. Problem? Switch back to blue in seconds

For Kubernetes: Argo Rollouts with automatic health checks. Rollout stops if metrics exceed threshold.

Canary Releases¶

Progressive rollout for large systems:

1. New version gets 5% traffic
2. Automatic metrics: error rate, latency, business KPIs
3. Metrics OK → 25% → 50% → 100%
4. Bad metrics → automatic rollback

Entire process: 30-60 minutes. Human intervention only on escalation. Argo Rollouts or Flagger for Kubernetes.

Feature Flags¶

Separating deploy from release:

• Code in production, feature disabled — deploy without risk
• Progressive enablement — internal → beta → 10% → 100%
• A/B testing — variant A vs. B, metrics decide
• Kill switch — instant disable of problematic feature
• Targeting — feature only for specific users/segments

Tools: LaunchDarkly, Unleash, custom solutions. CI/CD integration — feature flag automatically created when merging PR with feature flag annotation.

Database Migrations¶

The riskiest part of deployment. Rules:

Expand-Contract Pattern: 1. Expand — Add new column, keep the old one 2. Migrate — Copy/transform data 3. Switch — Application reads from new column 4. Contract — Remove old column

No ALTER TABLE with locks. No DROP COLUMN during deployment. Every migration is rollbackable.

CI/CD Pipeline¶

┌─────────┐   ┌──────────┐   ┌──────────┐   ┌─────────┐   ┌──────────┐
│  Commit  │──▶│  Build   │──▶│  Test    │──▶│  Stage  │──▶│  Prod    │
│          │   │  + Lint  │   │  Unit    │   │  E2E    │   │  Canary  │
│          │   │  + SAST  │   │  Integ   │   │  Smoke  │   │  → Full  │
└─────────┘   └──────────┘   └──────────┘   └─────────┘   └──────────┘
                                                                │
                                                          Auto rollback
                                                          on threshold

Commit → production in < 15 minutes. Automated. With quality gates at every step.

Souvisí s