Deployment Patterns

# Deployment Patterns

Production deployment workflows and CI/CD best practices.

## When to Activate

- Setting up CI/CD pipelines
- Dockerizing an application
- Planning deployment strategy (blue-green, canary, rolling)
- Implementing health checks and readiness probes
- Preparing for a production release
- Configuring environment-specific settings

## Deployment Strategies

### Rolling Deployment (Default)

Replace instances gradually — old and new versions run simultaneously during rollout.

```
Instance 1: v1 → v2  (update first)
Instance 2: v1        (still running v1)
Instance 3: v1        (still running v1)

Instance 1: v2
Instance 2: v1 → v2  (update second)
Instance 3: v1

Instance 1: v2
Instance 2: v2
Instance 3: v1 → v2  (update last)
```

**Pros:** Zero downtime, gradual rollout
**Cons:** Two versions run simultaneously — requires backward-compatible changes
**Use when:** Standard deployments, backward-compatible changes

### Blue-Green Deployment

Run two identical environments. Switch traffic atomically.

```
Blue  (v1) ← traffic
Green (v2)   idle, running new version

# After verification:
Blue  (v1)   idle (becomes standby)
Green (v2) ← traffic
```

**Pros:** Instant rollback (switch back to blue), clean cutover
**Cons:** Requires 2x infrastructure during deployment
**Use when:** Critical services, zero-tolerance for issues

### Canary Deployment

Route a small percentage of traffic to the new version first.