Demo - Voting application 1

This notes is for the course Kuberenetes for absolute beginners

Application flow

K8s nodes — **K8s Pods demo**: https://www.udemy.com/course/learn-kubernetes/

Voting application

We create pods and expose the container port. Please note that all the docker images are pre-built and this demo is to understand how different microservices communicate with each other through k8s services.

Create a definition for pod voting-app-pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: voting-app-pod
  labels:
    name: voting-app-pod
    app: demo-voting-app
spec:
  containers:
    - name: voting-app
      image: dockersamples/examplevotingapp_vote
      imagePullPolicy: IfNotPresent
      ports:
        - containerPort: 80
  restartPolicy: Always

Create a Loadbalancer service to expose the application to external world voting-app-service.yml

apiVersion: v1
kind: Service
metadata:
  name: voting-service
  labels:
    name: voting-service
    app: demo-voting-app
spec:
  ports:
    - port: 80
      targetPort: 80
  selector:
    name: voting-app-pod
    app: demo-voting-app
  type: LoadBalancer

Result application

Create a definition for a pod result-app-pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: result-app-pod
  labels:
    name: result-app-pod
    app: demo-voting-app
spec:
  containers:
    - name: result-app
      image: dockersamples/examplevotingapp_result
      imagePullPolicy: IfNotPresent
      ports:
        - containerPort: 80
  restartPolicy: Always

Create a Loadbalancer service to expose the application to external world result-app-service.yml

apiVersion: v1
kind: Service
metadata:
  name: result-service
  labels:
    name: result-service
    app: demo-voting-app
spec:
  ports:
    - port: 80
      targetPort: 80
  selector:
    name: result-app-pod
    app: demo-voting-app
  type: LoadBalancer

Redis application

Create a definition for a pod redis-pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: redis-pod
  labels:
    name: redis-pod
    app: demo-voting-app
spec:
  containers:
    - name: redis
      image: redis
      imagePullPolicy: IfNotPresent
      ports:
        - containerPort: 6379
  restartPolicy: Always

Create a NodePort service for postgres redis-service.yml

apiVersion: v1
kind: Service
metadata:
  name: redis
  labels:
    name: redis-service
    app: demo-voting-app
spec:
  ports:
    - port: 6379
      targetPort: 6379
  selector:
    name: redis-pod
    app: demo-voting-app
  type: NodePort

Services are created so that the pods can communicate to each other.

Services should be named based on what other applications are looking for. The name here is set to db because the application looks for service named db (you can see that in the code).

Postgres application

Create a definition for a pod postgres-pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: postgres-pod
  labels:
    name: postgres-pod
    app: demo-voting-app
spec:
  containers:
    - name: postgres
      image: postgres:9.4
      imagePullPolicy: IfNotPresent
      env:
        - name: POSTGRES_USER
          value: "postgres"
        - name: POSTGRES_PASSWORD
          value: "postgres"
        - name: POSTGRES_HOST_AUTH_METHOD
          value: trust
      ports:
        - containerPort: 5432
  restartPolicy: Always

Create a NodePort service for postgres postgres-service.yml

apiVersion: v1
kind: Service
metadata:
  name: db
  labels:
    name: db-service
    app: demo-voting-app
spec:
  ports:
    - port: 5432
      targetPort: 5432
  selector:
    name: postgres-pod
    app: demo-voting-app
  type: NodePort

Worker application

Note that these pod is needed just for internal communication.

Create a definition for a pod worker-app-pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: worker-app-pod
  labels:
    name: worker-app-pod
    app: demo-voting-app
spec:
  containers:
    - name: worker-app
      image: dockersamples/examplevotingapp_worker
      imagePullPolicy: IfNotPresent
  restartPolicy: Always

Output

Application communication (in docker)

Note that links is deprecated but this gives an idea of how the applications communicate internally.

Demo - Voting application 1