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Module 10 - Deploying a stateless application

This tutorial shows you how to build and deploy a simple (not production ready), multi-tier web application using Kubernetes and Docker. This example consists of the following components:

  • A single-instance Redis to store guestbook entries
  • Multiple web frontend instances

Objectives

  • Start up a Redis leader.
  • Start up two Redis followers.
  • Start up the guestbook frontend.
  • Expose and view the Frontend Service.
  • Clean up.

Start up the Redis Database

The guestbook application uses Redis to store its data.

Creating the Redis Deployment

The manifest file, included below, specifies a Deployment controller that runs a single replica Redis Pod.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-leader
  labels:
    app: redis
    role: leader
    tier: backend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
        role: leader
        tier: backend
    spec:
      containers:
      - name: leader
        image: "docker.io/redis:6.0.5"
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379

  1. Apply the Redis Deployment from the redis-leader-deployment.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/redis-leader-deployment.yaml

  2. Query the list of Pods to verify that the Redis Pod is running:

    kubectl get pods

    The response should be similar to this:

    NAME                           READY   STATUS    RESTARTS   AGE
redis-leader-fb76b4755-xjr2n   1/1     Running   0          13s

  3. Run the following command to view the logs from the Redis leader Pod:

    kubectl logs -f deployment/redis-leader

Creating the Redis leader Service

The guestbook application needs to communicate to the Redis to write its data. You need to apply a Service to proxy the traffic to the Redis Pod. A Service defines a policy to access the Pods.

apiVersion: v1
kind: Service
metadata:
  name: redis-leader
  labels:
    app: redis
    role: leader
    tier: backend
spec:
  ports:
  - port: 6379
    targetPort: 6379
  selector:
    app: redis
    role: leader
    tier: backend

  1. Apply the Redis Service from the following redis-leader-service.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/redis-leader-service.yaml

  2. Query the list of Services to verify that the Redis Service is running:

    kubectl get service

    The response should be similar to this:

    NAME           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
redis-leader   ClusterIP   10.103.78.24 <none>        6379/TCP   16s

Set up Redis followers

Although the Redis leader is a single Pod, you can make it highly available and meet traffic demands by adding a few Redis followers, or replicas.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-follower
  labels:
    app: redis
    role: follower
    tier: backend
spec:
  replicas: 2
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
        role: follower
        tier: backend
    spec:
      containers:
      - name: follower
        image: gcr.io/google_samples/gb-redis-follower:v2
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379

  1. Apply the Redis Deployment from the following redis-follower-deployment.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/redis-follower-deployment.yaml

  2. Verify that the two Redis follower replicas are running by querying the list of Pods:

    kubectl get pods

    The response should be similar to this:

    NAME                             READY   STATUS    RESTARTS   AGE
redis-follower-dddfbdcc9-82sfr   1/1     Running   0          37s
redis-follower-dddfbdcc9-qrt5k   1/1     Running   0          38s
redis-leader-fb76b4755-xjr2n     1/1     Running   0          11m

Creating the Redis follower service

The guestbook application needs to communicate with the Redis followers to read data. To make the Redis followers discoverable, you must set up another Service.

apiVersion: v1
kind: Service
metadata:
  name: redis-follower
  labels:
    app: redis
    role: follower
    tier: backend
spec:
  ports:
    # the port that this service should serve on
  - port: 6379
  selector:
    app: redis
    role: follower
    tier: backend

  1. Apply the Redis Service from the following redis-follower-service.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/redis-follower-service.yaml

  2. Query the list of Services to verify that the Redis Service is running:

    kubectl get service

    The response should be similar to this:

    NAME             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
redis-follower   ClusterIP   10.110.162.42   <none>        6379/TCP   9s
redis-leader     ClusterIP   10.103.78.24    <none>        6379/TCP   6m10s

Set up and Expose the Guestbook Frontend

Now that you have the Redis storage of your guestbook up and running, start the guestbook web servers. Like the Redis followers, the frontend is deployed using a Kubernetes Deployment.

The guestbook app uses a PHP frontend. It is configured to communicate with either the Redis follower or leader Services, depending on whether the request is a read or a write. The frontend exposes a JSON interface, and serves a jQuery-Ajax-based UX.

Creating the Guestbook Frontend Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
        app: guestbook
        tier: frontend
  template:
    metadata:
      labels:
        app: guestbook
        tier: frontend
    spec:
      containers:
      - name: php-redis
        image: gcr.io/google_samples/gb-frontend:v5
        env:
        - name: GET_HOSTS_FROM
          value: "dns"
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 80

  1. Apply the frontend Deployment from the frontend-deployment.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/frontend-deployment.yaml

  2. Query the list of Pods to verify that the three frontend replicas are running:

    kubectl get pods -l app=guestbook -l tier=frontend

    The response should be similar to this:

    NAME                        READY   STATUS    RESTARTS   AGE
frontend-85595f5bf9-5tqhb   1/1     Running   0          47s
frontend-85595f5bf9-qbzwm   1/1     Running   0          47s
frontend-85595f5bf9-zchwc   1/1     Running   0          47s

Creating the Frontend Service

The Redis Services you applied is only accessible within the Kubernetes cluster because the default type for a Service is ClusterIP. ClusterIP provides a single IP address for the set of Pods the Service is pointing to. This IP address is accessible only within the cluster.

If you want guests to be able to access your guestbook, you must configure the frontend Service to be externally visible, so a client can request the Service from outside the Kubernetes cluster. However a Kubernetes user you can use kubectl port-forward to access the service even though it uses a ClusterIP.

apiVersion: v1
kind: Service
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  ports:
    # the port that this service should serve on
  - port: 80
  selector:
    app: guestbook
    tier: frontend

  1. Apply the frontend Service from the frontend-service.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/frontend-service.yaml

  2. Query the list of Services to verify that the frontend Service is running:

    kubectl get services

    The response should be similar to this:

    NAME             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
frontend         ClusterIP   10.97.28.230    <none>        80/TCP     19s
redis-follower   ClusterIP   10.110.162.42   <none>        6379/TCP   5m48s
redis-leader     ClusterIP   10.103.78.24    <none>        6379/TCP   11m

Viewing the Frontend Service via kubectl port-forward

  1. Run the following command to forward port 8080 on your local machine to port 80 on the service.

    kubectl port-forward svc/frontend 8080:80

    The response should be similar to this:

    Forwarding from 127.0.0.1:8080 -> 80
Forwarding from [::1]:8080 -> 80

  2. load the page http://localhost:8080 in your browser to view your guestbook.

Hint: In AWS Cloud9 use Tools -> Preview -> Preview running applications to open the browser on the appropriate remote address.

Try adding some guestbook entries by typing in a message, and clicking Submit. The message you typed appears in the frontend. This message indicates that data is successfully added to Redis through the Services you created earlier.

Use CTRL-C to stop the proxy.

Configure a public Ingress for the Service

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: guestbook-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /$2
    nginx.ingress.kubernetes.io/configuration-snippet: |
      rewrite ^([^.?]*[^/])$ $1/ redirect;
spec:
  ingressClassName: nginx
  rules:
  - http:
      paths:
      - path: /group-1(/|$)(.*)
        pathType: Prefix
        backend:
          service:
            name: frontend
            port:
              number: 80

Change your groups path name and deploy:

kubectl apply -f path_to_ingress_file

Viewing the Frontend Service via Ingress

Retrieve the Ingress resource and wait for the external IP address/DNS to view your Guestbook:

  1. Run the following command to get the IP address for the frontend Service.

    kubectl get ingress guestbook-ingress

    The response should be similar to this:

NAME                CLASS   HOSTS   ADDRESS                                                                         PORTS   AGE
guestbook-ingress   nginx   *       a30be3be54566445c86ca3a56e736230-788d26b13fc29c22.elb.us-east-1.amazonaws.com   80      5m3s
  1. Copy the external IP/DNS address, and load the page in your browser to view your guestbook. Make sure to append your path postfix, e.g., /group-1.
a30be3be54566445c86ca3a56e736230-788d26b13fc29c22.elb.us-east-1.amazonaws.com/group-1

Cleanup

Deleting the Deployments and Services also deletes any running Pods. Use labels to delete multiple resources with one command.

  1. Run the following commands to delete all Pods, Deployments, and Services.

    kubectl delete deployment -l app=redis
kubectl delete service -l app=redis
kubectl delete deployment frontend
kubectl delete service frontend
kubectl delete ingress guestbook-ingress

    The response should look similar to this:

deployment.apps "redis-follower" deleted
deployment.apps "redis-leader" deleted
deployment.apps "frontend" deleted
service "frontend" deleted

  1. Query the list of Pods to verify that no Pods are running:

    kubectl get pods

    The response should look similar to this:

    No resources found in default namespace.

Adapted from https://kubernetes.io/docs/tutorials/stateless-application/guestbook/ licenced under Creative Commons Attribution 4.0 International.