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Services

Your Deployment runs 3 pods, but each has its own IP address that changes whenever a pod is replaced. You can't hard-code an address that keeps moving. A Service solves this by giving your set of pods one stable name and address, and it load-balances requests across all the healthy pods behind it.

The Service finds its pods using the same label the Deployment stamped on them: app: web. Labels are the glue that connects Kubernetes objects together.

🔌 Create a Service​

Open k8s/service.yaml. Note:

  • selector: app: web - which pods this Service sends traffic to
  • port: 80 - the port the Service listens on inside the cluster
  • targetPort: 3000 - the port your app listens on inside each pod

  1. Apply the Service:

    kubectl apply -f k8s/service.yaml

  2. Look at it. The default type is ClusterIP - reachable from inside the cluster:

    kubectl get service web

  3. Confirm it found your pods. The endpoints list should show 3 pod IPs:

    kubectl get endpoints web

    Three endpoints means the Service successfully matched all three pods via the app: web label. ✅

⚖️ Watch the load balancing​

Inside the cluster, the Service is reachable by its name (web) thanks to cluster DNS. Let's send it several requests and watch them get spread across different pods.

You'll launch a tiny throwaway pod that makes 6 requests to the Service and then deletes itself:

kubectl run client --rm -i --restart=Never --image=busybox -- \
  sh -c 'for i in $(seq 1 6); do wget -qO- http://web/api; done'

Look at the pod field in the responses - you'll see different pod names as the Service distributes your requests across all three replicas:

{"version":"1.0","pod":"web-7d9c8b6f5-abc12"}
{"version":"1.0","pod":"web-7d9c8b6f5-xy789"}
{"version":"1.0","pod":"web-7d9c8b6f5-abc12"}
{"version":"1.0","pod":"web-7d9c8b6f5-qr456"}
...
note

The client reached your app at simply http://web/ - no IP addresses, no hard-coded pod names. That stable name is the whole point of a Service. As pods come and go, the name keeps working.

🧠 The big idea​

  • Pods are disposable and have changing IPs.
  • A Service gives a group of pods one durable address and load-balances across them.
  • Labels and selectors are how Kubernetes wires objects to each other.

Your app is now reliably reachable inside the cluster. Next you'll make it more powerful - scaling it up and rolling out a new version without dropping a single request. 📈