Deployment Rules

Pre-Deploy Checklist

• Tests passing in CI — never deploy with failing tests
• Environment variables set in target — missing secrets cause silent failures
• Database migrations run before code deploy — new code expecting new schema fails
• Rollback plan ready — know exactly how to revert before you need to

Deployment Strategies

• Rolling: update instances one by one — safe, slower, no extra resources
• Blue-green: full parallel environment, instant switch — fast rollback, 2x resources
• Canary: route percentage to new version — catch issues early, complex routing
• Choose based on risk tolerance and resources — no universal best

Zero-Downtime Deploys

• Health checks must pass before traffic routes — unhealthy instances stay out
• Graceful shutdown: finish in-flight requests before terminating
• Database changes must be backwards compatible — old code still running during deploy
• Session handling: sticky sessions or external session store — don't lose user state