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World C3: Release & Deploy

Recreate, rolling, blue/green, canary

You will learn: four ways to swap old code for new, and when each one fits.

Checked with GitHub Actions 2026-10 on 31 Oct 2026

The problem

Tap each point on the timeline.

Friday, 5 pm. One push sends the new version to everyone. It has a bug. Tap each moment. How could it hurt fewer people?

Watch

Way 1: recreate: Stop the old version, then start the new one. Like closing the stall to swap the menu: users wait.. Close the stall, swap the menu, open again. The old version stops, then the new one starts. What do customers see in between?

Watch

Way 2: rolling update: Swap the copies one at a time, like changing cooks one by one. The stall never closes.. Swap the cooks one at a time. The stall never closes. Put the steps in order.

First step at the top. Put these in order. Use the arrows, or drag.

  • Stop one copy of version 1
  • Check that it is healthy
  • Repeat until every copy is version 2
  • Start one copy of version 2

Try it

Way 3: blue/green deployment: Two full kitchens. Test the new one, then flip the sign so everyone goes there. Flip back to undo.. Two full kitchens. Version 2 waits next to version 1. Test it, then switch everyone. Trouble? Switch back.

v2 is ready next to v1. Test it, or switch. Switch back if errors jump.

Users now: 100% on v1 (old), 0% on v2 (new).

Error rate per minute
0%6%11%alarmminutes →

v1 (old) v2 (new)

Minute 0

Users who hit a v2 error: 0 (limit 150)

Numbers, minute by minute

No traffic yet.

Watch

Way 4: canary release: A few users get the new version first, like a few customers tasting a new dish. All good? Serve more.. A few customers taste the new dish first. All good? Serve more people. Sort each fact.

Drag a card into a box. Or tap the card, then tap the box.

      Try it

      Your turn. Send users to version 2, step by step. Watch the graph. Roll back before 150 users hit a bug.

      Send a few users to v2. Watch the graph. Roll back if errors jump.

      Users now: 100% on v1 (old), 0% on v2 (new).

      Error rate per minute
      0%6%11%alarmminutes →

      v1 (old) v2 (new)

      Minute 0

      Users who hit a v2 error: 0 (limit 150)

      Numbers, minute by minute

      No traffic yet.

      Predict

      Version 2 renames a database column. Version 1 crashes without the old name. Which way fits?

      You did it!

      You can now pick a safe way to swap versions.

      Go deeper (optional)

      Kubernetes does rolling updates by default (World K2). Cloudflare Workers can run a canary for you, called a gradual deployment. Upload a version with no traffic, then choose its share.

      bash
      npx wrangler versions upload
      npx wrangler versions deploy

      Real rep (optional): use a free test Worker, not your team’s. Send 10% to the new version, then roll back.