Zero-Downtime Rolling Updates: Automating Cloud Deployments, AMIs & Health Checks
Production web applications should never drop active HTTP requests or WebSocket connections during a code release. Whether deploying to an AWS Application Load Balancer + Auto Scaling Group or Google Cloud Run revisions, zero-downtime delivery relies on automated immutable artifacts and strict health-check gating.
1. Blue/Green & Rolling ASG Fleet Replacement
- Compile & Verify Assets: Build production Webpack/Next.js bundles, run automated unit tests, and execute database migrations safely (using expand-and-contract schema patterns).
- Immutable Image Snapshot: Capture a versioned AMI / container image and register a new Launch Template or Cloud Run revision.
- Scale Out & Warm Up: Launch the new instance alongside the existing one and poll Target Group health checks until 5 consecutive 200 OK checks pass.
- Connection Draining & CDN Invalidation: Gracefully drain and terminate the old revision, then purge edge CDN caches.