World K2: Trays & Orders

Blue/green and canary with Deployments

You will learn: blue/green with a Service selector switch, and a canary with replica counts.

Checked with Kubernetes 1.37 on 31 Oct 2026

The problem

Menu version 2 is ready. You want it live in one second. If it is bad, gone in one second. With plain Kubernetes objects, how?

Watch

You are here: cluster kind-dev namespace default

~/shop $ kubectl get deploymentsNAME         READY   UP-TO-DATE   AVAILABLE   AGEshop-blue    2/2     2            2           16sshop-green   2/2     2            2           16s~/shop $ kubectl get service shop -o wideNAME   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE   SELECTORshop   ClusterIP   10.96.151.105   <none>        80/TCP    16s   app=shop,version=blue~/shop $ kubectl exec client -- wget -qO- -T 5 http://shop<h1>Kedai Kancil menu v1</h1>

: two full Deployments run side by side. The Service selector says version=blue, so only blue trays get customers.

Try it

Your turn. service-green.yaml is the same order number, pointing at green. Apply it. Then ask the shop again from client.

You are here: cluster kind-dev namespace default

shop2/2 ready

dev-control-planeOpenManager

No trays here.

dev-workerOpen

client
shop·gl7xh
shop·68n9z

dev-worker2Open

shop·kw9rw
shop·nhlrr

Time: +0s (sped up)

Hint

kubectl apply -f service-green.yaml, then kubectl exec client -- wget -qO- -T 5 http://shop.

Predict

Green has a bug. How fast can you go back to blue?

Watch

You are here: cluster kind-dev namespace default

~/shop $ kubectl apply -f canary.yamldeployment.apps/shop-canary created~/shop $ kubectl rollout status deployment/shop-canary --timeout=120sWaiting for deployment "shop-canary" rollout to finish: 0 of 1 updated replicas are available...deployment "shop-canary" successfully rolled out~/shop $ kubectl get deploymentsNAME          READY   UP-TO-DATE   AVAILABLE   AGEshop-canary   1/1     1            1           4sshop-stable   3/3     3            3           20s~/shop $ kubectl get endpointslices -l kubernetes.io/service-name=shopNAME         ADDRESSTYPE   PORTS   ENDPOINTS                                      AGEshop-c8v4d   IPv4          80      10.244.2.4,10.244.1.3,10.244.2.3 + 1 more...   20s

: a second Deployment with the same app: shop label, but only 1 tray. The Service picks all 4, so about 1 in 4 customers tastes version 2.

Try it

Real traffic, real errors. Move customers to version 2 step by step. Roll back before 150 of them hit the 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

v1 (old) v2 (new)

Minute 0

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

Numbers, minute by minute

No traffic yet.

Check

Blue/green or canary? Sort each fact.

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

You did it!

You can now run blue/green and canary releases with plain Deployments.

Go deeper (optional)

Where the story breaks: a real tray is a running program. A stall is a whole computer. A replica canary is rough: 1 of 4 is 25%, not 5%. For exact shares, use Gateway API weights (World K3) or Argo Rollouts (World K7).

Real rep (optional): on a throwaway cluster, switch a Service selector, then switch it back.