Lesson 15 / 21
Blue-Green Deployment
Two full environments; switch traffic instantly, roll back just as fast.
How it works
Keep two identical production environments, blue (live) and green (idle). Deploy the new version to green, verify it, then switch the router so all traffic hits green — blue becomes the idle standby.
Two identical stages
Like a theater with two identical stages side by side. The new act rehearses fully on the dark stage, and only when it's ready does the spotlight switch — the audience never sees an in-between state.
Instant rollback
If something's wrong after the switch, flip the router back to blue immediately — no redeploy needed. The cost is running two full production environments at once.