Why not all at once
A buggy new version pushed to everyone hits all users instantly, with no time to roll back. Progressive releases shrink the risk so a problem touches only a few.
Canary release
Roll out by traffic percentage: 1% internal first, then 5%, 20%, 100% as metrics stay healthy. Stop and revert at any anomaly. Good for real-traffic validation.
Blue-green deployment
Run two environments: blue (old) serves traffic while green (new) is ready; flip routing to green in a second. Flip back to blue on trouble, users barely notice. Cost is double resources.
Rollback matters more than ship
- Keep the previous version: blue-green has a backup by design; canary must scale back to 0% in one click;
- Watch metrics before scaling: stop on errors, latency or conversion spikes;
- Backward-compatible schema: new code reads the old table, so rollback will not crash.