Communicate two microservices in a Kubernetes cluster

First we create a deployment and a service to communicate to

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: webapp1
  template:
    metadata:
      labels:
        app: webapp1
    spec:
      containers:
      - name: webapp1
        image: katacoda/docker-http-server:latest
        ports:
        - containerPort: 80

---

apiVersion: v1
kind: Service
metadata:
  name: web-app-service
spec:
  selector:
    app: webapp1
  ports:
    - protocol: TCP
      port: 80

Save as web-app-service.yaml and run the following command

    kubectl create -f web-app-service.yaml

When a Pod is executed inside a Node, the kubelet adds to it a set of environment variables that include the HOST and PORT of every running service: {SVCNAME}_SERVICE_HOST` y `{SVCNAME}_SERVICE_PORT.

If our service name is web_app_service then we get the environment variables: WEB_APP_SERVICE_SERVICE_HOST and WEB_APP_SERVICE_SERVICE_PORT

Then we can pass these as envrionment variables of the second service, and the cluster will keep them actualized, even if the HOST and/or PORT changes.

Reference Links

• https://kubernetes.io/docs/concepts/services-networking/service/