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Example: Deploying PHP Guestbook application with Redis

This tutorial shows you how to build and deploy a simple, multi-tier web application using Kubernetes and Docker. This example consists of the following components:

  • A single-instance Redis master to store guestbook entries
  • Multiple replicated Redis instances to serve reads
  • Multiple web frontend instances

Objectives

  • Start up a Redis master.
  • Start up Redis slaves.
  • Start up the guestbook frontend.
  • Expose and view the Frontend Service.
  • Clean up.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

Start up the Redis Master

The guestbook application uses Redis to store its data. It writes its data to a Redis master instance and reads data from multiple Redis slave instances.

Creating the Redis Master Deployment

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

application/guestbook/redis-master-deployment.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: redis-master
  labels:
    app: redis
spec:
  selector:
    matchLabels:
      app: redis
      role: master
      tier: backend
  replicas: 1
  template:
    metadata:
      labels:
        app: redis
        role: master
        tier: backend
    spec:
      containers:
      - name: master
        image: k8s.gcr.io/redis:e2e  # or just image: redis
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379
  1. Launch a terminal window in the directory you downloaded the manifest files.

  2. Apply the Redis Master Deployment from the redis-master-deployment.yaml file:

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

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

      kubectl get pods

    The response should be similar to this:

      NAME                            READY     STATUS    RESTARTS   AGE
  redis-master-1068406935-3lswp   1/1       Running   0          28s

  4. Run the following command to view the logs from the Redis Master Pod:

     kubectl logs -f POD-NAME
Note: Replace POD-NAME with the name of your Pod.

Creating the Redis Master Service

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

application/guestbook/redis-master-service.yaml 
apiVersion: v1
kind: Service
metadata:
  name: redis-master
  labels:
    app: redis
    role: master
    tier: backend
spec:
  ports:
  - port: 6379
    targetPort: 6379
  selector:
    app: redis
    role: master
    tier: backend

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

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

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

      kubectl get service

    The response should be similar to this:

      NAME           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
  kubernetes     ClusterIP   10.0.0.1     <none>        443/TCP    1m
  redis-master   ClusterIP   10.0.0.151   <none>        6379/TCP   8s
Note: This manifest file creates a Service named redis-master with a set of labels that match the labels previously defined, so the Service routes network traffic to the Redis master Pod.

Start up the Redis Slaves

Although the Redis master is a single pod, you can make it highly available to meet traffic demands by adding replica Redis slaves.

Creating the Redis Slave Deployment

Deployments scale based off of the configurations set in the manifest file. In this case, the Deployment object specifies two replicas.

If there are not any replicas running, this Deployment would start the two replicas on your container cluster. Conversely, if there are more than two replicas are running, it would scale down until two replicas are running.

application/guestbook/redis-slave-deployment.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: redis-slave
  labels:
    app: redis
spec:
  selector:
    matchLabels:
      app: redis
      role: slave
      tier: backend
  replicas: 2
  template:
    metadata:
      labels:
        app: redis
        role: slave
        tier: backend
    spec:
      containers:
      - name: slave
        image: gcr.io/google_samples/gb-redisslave:v3
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        env:
        - name: GET_HOSTS_FROM
          value: dns
          # Using `GET_HOSTS_FROM=dns` requires your cluster to
          # provide a dns service. As of Kubernetes 1.3, DNS is a built-in
          # service launched automatically. However, if the cluster you are using
          # does not have a built-in DNS service, you can instead
          # access an environment variable to find the master
          # service's host. To do so, comment out the 'value: dns' line above, and
          # uncomment the line below:
          # value: env
        ports:
        - containerPort: 6379

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

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

  2. Query the list of Pods to verify that the Redis Slave Pods are running:

      kubectl get pods

    The response should be similar to this:

      NAME                            READY     STATUS              RESTARTS   AGE
  redis-master-1068406935-3lswp   1/1       Running             0          1m
  redis-slave-2005841000-fpvqc    0/1       ContainerCreating   0          6s
  redis-slave-2005841000-phfv9    0/1       ContainerCreating   0          6s

Creating the Redis Slave Service

The guestbook application needs to communicate to Redis slaves to read data. To make the Redis slaves discoverable, you need to set up a Service. A Service provides transparent load balancing to a set of Pods.

application/guestbook/redis-slave-service.yaml 
apiVersion: v1
kind: Service
metadata:
  name: redis-slave
  labels:
    app: redis
    role: slave
    tier: backend
spec:
  ports:
  - port: 6379
  selector:
    app: redis
    role: slave
    tier: backend

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

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

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

      kubectl get services

    The response should be similar to this:

      NAME           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
  kubernetes     ClusterIP   10.0.0.1     <none>        443/TCP    2m
  redis-master   ClusterIP   10.0.0.151   <none>        6379/TCP   1m
  redis-slave    ClusterIP   10.0.0.223   <none>        6379/TCP   6s

Set up and Expose the Guestbook Frontend

The guestbook application has a web frontend serving the HTTP requests written in PHP. It is configured to connect to the redis-master Service for write requests and the redis-slave service for Read requests.

Creating the Guestbook Frontend Deployment

application/guestbook/frontend-deployment.yaml 
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: frontend
  labels:
    app: guestbook
spec:
  selector:
    matchLabels:
      app: guestbook
      tier: frontend
  replicas: 3
  template:
    metadata:
      labels:
        app: guestbook
        tier: frontend
    spec:
      containers:
      - name: php-redis
        image: gcr.io/google-samples/gb-frontend:v4
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        env:
        - name: GET_HOSTS_FROM
          value: dns
          # Using `GET_HOSTS_FROM=dns` requires your cluster to
          # provide a dns service. As of Kubernetes 1.3, DNS is a built-in
          # service launched automatically. However, if the cluster you are using
          # does not have a built-in DNS service, you can instead
          # access an environment variable to find the master
          # service's host. To do so, comment out the 'value: dns' line above, and
          # uncomment the line below:
          # value: env
        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-3823415956-dsvc5   1/1       Running   0          54s
  frontend-3823415956-k22zn   1/1       Running   0          54s
  frontend-3823415956-w9gbt   1/1       Running   0          54s

Creating the Frontend Service

The redis-slave and redis-master Services you applied are only accessible within the container 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 container cluster. Minikube can only expose Services through NodePort.

Note: Some cloud providers, like Google Compute Engine or Google Kubernetes Engine, support external load balancers. If your cloud provider supports load balancers and you want to use it, simply delete or comment out type: NodePort, and uncomment type: LoadBalancer.
application/guestbook/frontend-service.yaml 
apiVersion: v1
kind: Service
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # comment or delete the following line if you want to use a LoadBalancer
  type: NodePort 
  # if your cluster supports it, uncomment the following to automatically create
  # an external load-balanced IP for the frontend service.
  # type: LoadBalancer
  ports:
  - 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       NodePort    10.0.0.112   <none>       80:31323/TCP   6s
  kubernetes     ClusterIP   10.0.0.1     <none>        443/TCP        4m
  redis-master   ClusterIP   10.0.0.151   <none>        6379/TCP       2m
  redis-slave    ClusterIP   10.0.0.223   <none>        6379/TCP       1m

Viewing the Frontend Service via NodePort

If you deployed this application to Minikube or a local cluster, you need to find the IP address to view your Guestbook.

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

      minikube service frontend --url

    The response should be similar to this:

      http://192.168.99.100:31323

  2. Copy the IP address, and load the page in your browser to view your guestbook.

Viewing the Frontend Service via LoadBalancer

If you deployed the frontend-service.yaml manifest with type: LoadBalancer you need to find the IP address to view your Guestbook.

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

      kubectl get service frontend

    The response should be similar to this:

      NAME       TYPE        CLUSTER-IP      EXTERNAL-IP        PORT(S)        AGE
  frontend   ClusterIP   10.51.242.136   109.197.92.229     80:32372/TCP   1m

  2. Copy the external IP address, and load the page in your browser to view your guestbook.

Scale the Web Frontend

Scaling up or down is easy because your servers are defined as a Service that uses a Deployment controller.

  1. Run the following command to scale up the number of frontend Pods:

      kubectl scale deployment frontend --replicas=5

  2. Query the list of Pods to verify the number of frontend Pods running:

      kubectl get pods

    The response should look similar to this:

      NAME                            READY     STATUS    RESTARTS   AGE
  frontend-3823415956-70qj5       1/1       Running   0          5s
  frontend-3823415956-dsvc5       1/1       Running   0          54m
  frontend-3823415956-k22zn       1/1       Running   0          54m
  frontend-3823415956-w9gbt       1/1       Running   0          54m
  frontend-3823415956-x2pld       1/1       Running   0          5s
  redis-master-1068406935-3lswp   1/1       Running   0          56m
  redis-slave-2005841000-fpvqc    1/1       Running   0          55m
  redis-slave-2005841000-phfv9    1/1       Running   0          55m

  3. Run the following command to scale down the number of frontend Pods:

      kubectl scale deployment frontend --replicas=2

  4. Query the list of Pods to verify the number of frontend Pods running:

      kubectl get pods

    The response should look similar to this:

      NAME                            READY     STATUS    RESTARTS   AGE
  frontend-3823415956-k22zn       1/1       Running   0          1h
  frontend-3823415956-w9gbt       1/1       Running   0          1h
  redis-master-1068406935-3lswp   1/1       Running   0          1h
  redis-slave-2005841000-fpvqc    1/1       Running   0          1h
  redis-slave-2005841000-phfv9    1/1       Running   0          1h

Cleaning up

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 -l app=guestbook
  kubectl delete service -l app=guestbook

    The responses should be:

      deployment.apps "redis-master" deleted
  deployment.apps "redis-slave" deleted
  service "redis-master" deleted
  service "redis-slave" deleted
  deployment.apps "frontend" deleted    
  service "frontend" deleted

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

      kubectl get pods

    The response should be this:

      No resources found.

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