Guides

Blue-Green vs Canary on Kubernetes (Simple Walkthrough)

By Ravindra Bagale, DevOps trainer · LinkedIn · Published: 28 October 2026 · Last updated: 28 October 2026

Blue-green keeps two full versions and flips the Service selector; canary runs a small replica share first, then grows or aborts.

Language: English · मराठी · हिंदी

Why two styles

Releases fail; you need a rehearsed escape.

Why: In-place edits hide how to undo. What: Blue-green = full flip; canary = small percent. How: Labels + Service selector are the switch.

Example 1: Blue Deployment

Type this:

mkdir -p /tmp/bgc && printf '%s\n' 'apiVersion: apps/v1' 'kind: Deployment' 'metadata: {name: web-blue}' 'spec:' '  replicas: 2' '  selector: {matchLabels: {app: web, color: blue}}' '  template:' '    metadata: {labels: {app: web, color: blue}}' '    spec: {containers: [{name: web, image: public.ecr.aws/docker/library/nginx:1.27-alpine}]}' > /tmp/bgc/blue.yaml && grep color /tmp/bgc/blue.yaml | head -2

You will see:

selector: {matchLabels: {app: web, color: blue}}

What it means: Blue is the live color today.

Example 2: Green Deployment

Type this:

printf '%s\n' 'apiVersion: apps/v1' 'kind: Deployment' 'metadata: {name: web-green}' 'spec:' '  replicas: 2' '  selector: {matchLabels: {app: web, color: green}}' '  template:' '    metadata: {labels: {app: web, color: green}}' '    spec: {containers: [{name: web, image: public.ecr.aws/docker/library/nginx:1.27-alpine}]}' > /tmp/bgc/green.yaml && grep name /tmp/bgc/green.yaml | head -1

You will see:

metadata: {name: web-green}

What it means: Green sits idle until you flip the Service.

Example 3: Service points to blue

Type this:

printf '%s\n' 'apiVersion: v1' 'kind: Service' 'metadata: {name: web}' 'spec:' '  selector: {app: web, color: blue}' '  ports: [{port: 80}]' > /tmp/bgc/svc.yaml && grep color /tmp/bgc/svc.yaml

You will see:

selector: {app: web, color: blue}

What it means: Flip = change selector to green.

Concept 1: Blue-green flip

Change selector; traffic moves together.

Why: Half-updated Services confuse curl tests. What: patch svc selector to green. How: Roll back by patching to blue.

Example 4: Blue-green flip command

Type this:

printf '%s\n' 'kubectl patch svc web -p "{\"spec\":{\"selector\":{\"app\":\"web\",\"color\":\"green\"}}"'

You will see:

kubectl patch svc web -p "{"spec":{"selector":{"app":"web","color":"green"}}}"

What it means: All traffic moves in one step — Instant flip.

Example 8: Watch endpoints

Type this:

printf '%s\n' 'kubectl get endpoints web -o wide'

You will see:

kubectl get endpoints web -o wide

What it means: After a flip, endpoints must list the new pods.

Example 9: Rollback blue-green

Type this:

printf '%s\n' 'kubectl patch svc web -p "{\"spec\":{\"selector\":{\"app\":\"web\",\"color\":\"blue\"}}"'

You will see:

kubectl patch svc web -p "{"spec":{"selector":{"app":"web","color":"blue"}}}"

What it means: Flip back — old pods still warm.

Concept 2: Canary ratio

Few new pods share the Service.

Why: Exact percent needs a mesh; replica ratio is fine for labs. What: stable 9 + canary 1 ≈ 10%. How: Scale canary to 0 to abort.

Example 5: Canary weight idea

Type this:

printf '%s\n' 'canary: 10 percent pods on new version; 90 percent stay on stable'

You will see:

canary: 10 percent pods on new version; 90 percent stay on stable

What it means: Canary = small blast radius first.

Example 6: Two Deployments one Service (canary labels)

Type this:

printf '%s\n' 'Service selector app=web only; both stable and canary pods share app=web' 'Stable also has track=stable; canary has track=canary'

You will see:

Service selector app=web only; both stable and canary pods share app=web
Stable also has track=stable; canary has track=canary

What it means: Replica counts set the approximate percent.

Example 7: Canary scale math

Type this:

printf '%s\n' 'stable replicas=9; canary replicas=1  → about 10 percent'

You will see:

stable replicas=9; canary replicas=1  → about 10 percent

What it means: Exact percent needs a mesh; replica ratio is the beginner path.

Concept 3: Choose and clean

Capacity and risk decide.

Why: Wrong choice burns money or users. What: 2× capacity → blue-green; tight → canary. How: Delete lab YAML when done.

Example 10: Rollback canary

Type this:

printf '%s\n' 'kubectl scale deploy/web-canary --replicas=0'

You will see:

kubectl scale deploy/web-canary --replicas=0

What it means: Remove canary pods; stable keeps 100%.

Example 11: When to pick which

Type this:

printf '%s\n' 'blue-green: need instant rollback and double capacity ok' 'canary: want gradual risk on one cluster capacity'

You will see:

blue-green: need instant rollback and double capacity ok
canary: want gradual risk on one cluster capacity

What it means: Infosys runbooks pick canary when capacity is tight.

Example 12: Cleanup

Type this:

printf '%s\n' 'kubectl delete -f svc.yaml -f blue.yaml -f green.yaml'

You will see:

kubectl delete -f svc.yaml -f blue.yaml -f green.yaml

What it means: Lab cleanup.

Release card

1 Two Deployments 2 Service selector 3 Flip (blue-green) or ratio (canary) 4 Watch endpoints/errors 5 Roll back if needed

Suppose: endpoints empty after flip

Selector labels must match pod labels.

Suppose: canary percent wrong

Adjust replica counts; mesh for exact %.

Check yourself (quiz)

prepare → flip or canary → measure → finish or roll back. Did you understand? Let us try it once more.