Blue-Green Flow on Kubernetes

This repository demonstrates a simple Blue-Green deployment strategy on Kubernetes for a small Node.js web app. It contains:

• A sample app (Express) exposing / and /health on port 3000.
• Two Deployments (blue and green), a Service, and optional Ingress.
• Helper scripts to deploy a new image, switch traffic, port-forward for local testing, and run health checks.

Note: Filenames for the deployments use deployement-*.yaml (with an extra ‘e’) to match the current repo.

Architecture overview

• Namespace: blue-green-demo
• Deployments:
  • Blue: k8s/deployement-blue.yaml → Deployment/app-blue using image inestmimi123/blue-green-app:1.0.0
  • Green: k8s/deployement-green.yaml → Deployment/app-green using image inestmimi123/blue-green-app:1.1.0
• Service: k8s/service.yaml named web targets label selector app=web,color=<blue|green>
  • Default selector is color: blue so “blue” receives traffic initially.
• Ingress (optional): k8s/ingress.yaml for host bg.localtest.me routing to the web Service.

The app reports its color and version from environment variables and exposes a GET /health endpoint for probes and external checks.

Prerequisites

• A working Kubernetes cluster with kubectl configured.
• Optional: an Ingress controller (e.g., NGINX Ingress) if you plan to use the provided Ingress.
• If running the helper scripts:
  • They are Bash scripts meant for macOS/Linux. On Windows, run them under WSL or Git Bash. Alternatively, adapt the shown kubectl commands manually in PowerShell.

Quick start

1. Create the namespace

kubectl apply -f k8s/namespace.yaml

2. Deploy blue and green (both can exist; Service points to blue initially)

kubectl apply -f k8s/deployement-blue.yaml
kubectl apply -f k8s/deployement-green.yaml
kubectl apply -f k8s/service.yaml

3. (Optional) Apply Ingress

kubectl apply -f k8s/ingress.yaml

4. Access the app

• Port-forward the Service:

scripts/port_forward.sh
# or manually
kubectl -n blue-green-demo port-forward svc/web 8080:80

• Open:
  • http://localhost:8080/ → JSON info including color and version
  • http://localhost:8080/health → should return 200 OK

Blue-Green deployment flow

Assume blue is serving traffic and a new version should be rolled out to green.

1. Update the green deployment to a new image and wait for rollout

Using the helper script (Bash):

# Deploy new image to green and switch the Service selector to green once ready
scripts/deploy.sh green <REGISTRY>/<REPO>/blue-green-app:<TAG>

What the script does:

• kubectl set image on deployment/app-green (namespace blue-green-demo)
• Waits for rollout to complete
• Switches Service web selector to color: green

Manual commands equivalent:

# Set image and wait for rollout
kubectl -n blue-green-demo set image deployment/app-green app=<REGISTRY>/<REPO>/blue-green-app:<TAG>
kubectl -n blue-green-demo rollout status deployment/app-green

# Switch traffic to green
kubectl -n blue-green-demo patch service web -p '{"spec":{"selector":{"app":"web","color":"green"}}}'

2. Verify

With port-forward still active:

curl -fsS http://localhost:8080/health && echo OK
curl -fsS http://localhost:8080/ | jq .

Or use the provided script:

scripts/health_check.sh http://localhost:8080/health 30 1

3. Roll back (if needed)

To route traffic back to blue quickly:

scripts/switch_traffic.sh blue
# or manually
kubectl -n blue-green-demo patch service web -p '{"spec":{"selector":{"app":"web","color":"blue"}}}'

4. Scale down the idle color (optional)

To save resources you can scale down the non-active color after confidence:

kubectl -n blue-green-demo scale deployment/app-blue --replicas=0
# or for green if blue is active
kubectl -n blue-green-demo scale deployment/app-green --replicas=0

Building and publishing the app image

If you need to build your own image:

cd app
# Build image
docker build -t <REGISTRY>/<REPO>/blue-green-app:<TAG> .
# Push image
docker push <REGISTRY>/<REPO>/blue-green-app:<TAG>

Then use that image with the deployment flow above.

File reference

• app/Dockerfile — Node 20-alpine base, installs deps, runs npm start.
• app/src/server.js — Express server exposing / and /health.
• k8s/namespace.yaml — Creates namespace blue-green-demo.
• k8s/deployement-blue.yaml — Deployment app-blue, default image inestmimi123/blue-green-app:1.0.0.
• k8s/deployement-green.yaml — Deployment app-green, default image inestmimi123/blue-green-app:1.1.0.
• k8s/service.yaml — Service web, selector defaults to color: blue, port 80 → targetPort 3000.
• k8s/ingress.yaml — Ingress for host bg.localtest.me to Service web (requires Ingress controller).
• scripts/deploy.sh — Update target deployment image, wait for rollout, switch Service.
• scripts/switch_traffic.sh — Patch Service selector to blue or green and wait for endpoints.
• scripts/port_forward.sh — Port-forward web Service to localhost:8080.
• scripts/health_check.sh — Simple curl-based health checker.

Troubleshooting

• Probes failing: Ensure the container responds on /health and that targetPort matches containerPort (here 3000).
• Service not switching: Verify labels on Pods include both app=web and the correct color. Check with:

kubectl -n blue-green-demo get pods -l app=web -L color
kubectl -n blue-green-demo get svc web -o yaml
kubectl -n blue-green-demo get endpoints web -o wide

• Script usage on Windows: Run under WSL or Git Bash. Otherwise, copy the shown kubectl commands to PowerShell.

Advanced usage

• Windows users: scripts are Bash. Use WSL/Git Bash or run the equivalent kubectl commands shown.
• GitOps flow: This repo pairs with a GitOps repository (see Jenkinsfile env GITOPS_REPO_SSH). The pipeline updates deployment-green.yaml and switches Service selector via PR/commit.
• Health gates: Before switching traffic, ensure /health returns 200 for the target color. Example curl probes are provided.
• Rollback strategy: Switch back selector and optionally scale down the bad color. Keep both colors for fast recovery.

Jenkins pipeline overview

The included Jenkinsfile performs:

• Build Node app and Docker image, push to registry.
• Update GitOps repo with the new image in deployment-green and APP_VERSION env.
• Wait for GREEN health via HEALTH_URL.
• Switch Service selector to green. On failure, auto-rollback selector to blue.

Required Jenkins credentials:

• docker-registry: Docker username/password
• gitops-bot: credentials to push to the GitOps repo

Key env vars in Jenkinsfile:

• REGISTRY, APP_NAME, GITOPS_REPO_SSH, GITOPS_BRANCH, HEALTH_URL, NAMESPACE

Observability quick start

To add Prometheus metrics to the app, install prom-client and expose /metrics:

npm i prom-client

Add to app/src/server.js:

const client = require('prom-client');
client.collectDefaultMetrics();
app.get('/metrics', async (req, res) => {
  res.set('Content-Type', client.register.contentType);
  res.end(await client.register.metrics());
});

Then deploy kube-prometheus-stack and a ServiceMonitor as shown in GUIDE.md.

License

MIT