Create a multi-tier web application with Redis and PHP

This tutorial demonstrates how to build a multi-tier web application using Google Kubernetes Engine (GKE).

In this tutorial, you do the following:

  • Set up a web application with an external IP address and a load balancer.
  • Create a Redis cluster with a single master (leader) and multiple replicas (followers).

The example describes the following Kubernetes concepts:

Prepare the environment

To set up your environment, follow these steps:

  1. Set environment variables:

    export PROJECT_ID=PROJECT_ID
export COMPUTE_LOCATION=COMPUTE_LOCATION

    Replace the following:

  2. Clone the GitHub repository:

    git clone https://github.com/GoogleCloudPlatform/kubernetes-engine-samples

  3. Change to the working directory:

    cd kubernetes-engine-samples/quickstarts/guestbook/

Create a GKE cluster

Create an Autopilot or Standard GKE cluster:

Autopilot

gcloud container clusters create-auto guestbook \
    --location=${COMPUTE_LOCATION} \

Standard

gcloud container clusters create guestbook \
    --location=${COMPUTE_LOCATION} \
    --num-nodes=4

Connect to the cluster

Configure kubectl to communicate with the cluster:

gcloud container clusters get-credentials guestbook \
    --location=${COMPUTE_LOCATION}

Set up the Redis leader

The application uses Redis to store its data. The application writes its data to a Redis leader instance and reads data from multiple Redis follower instances.

  1. The following manifest describes a Kubernetes Deployment that runs a single replica Redis leader 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

    Apply the manifest to your cluster:

    kubectl apply -f redis-leader-deployment.yaml

  2. Verify that the Redis leader Pod is running:

    kubectl get pods

    The output is similar to the following:

    NAME                           READY     STATUS    RESTARTS   AGE
redis-leader-343230949-qfvrq   1/1       Running   0          43s

    It might take several minutes for STATUS to change from Pending to Running.

Create the Redis leader Service

The web application needs to communicate with the Redis leader to write its data. You can create a Service to proxy the traffic to the Redis leader Pod.

A Service is a Kubernetes abstraction that defines a logical set of Pods and a policy to enable access to the Pods. When you create a Service, you describe which Pods to proxy based on Pod labels.

  1. The following manifest describes a Service for the Redis leader:

    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

    This manifest includes a set of label selectors. These labels match the set of labels that are deployed in the previous step. Therefore, this Service routes the network traffic to the Redis leader Pod created in a previous step.

    The ports section of the manifest declares a single port mapping. The Service routes the traffic on port: 6379 to the targetPort: 6379 of the containers that match the specified selector labels. The containerPort used in the Deployment must match the targetPort to route traffic to the Deployment.

    Apply the manifest to your cluster:

    kubectl apply -f redis-leader-service.yaml

  2. Verify that GKE created the Service:

    kubectl get service

    The output is similar to the following:

    NAME           CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
kubernetes     10.51.240.1     <none>        443/TCP    42s
redis-leader   10.51.242.233   <none>        6379/TCP   12s

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.

  1. The following manifest describes a Deployment for the Redis follower Pods:

    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: us-docker.pkg.dev/google-samples/containers/gke/gb-redis-follower:v2
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379

  2. Apply the manifest to your cluster:

    kubectl apply -f redis-follower-deployment.yaml

  3. Verify that the two Redis follower replicas are running:

    kubectl get pods

    The output is similar to the following:

    NAME                              READY   STATUS    RESTARTS   AGE
redis-follower-76588f55b7-bnsq6   1/1     Running   0          27s
redis-follower-76588f55b7-qvtws   1/1     Running   0          27s
redis-leader-dd446dc55-kl7nl      1/1     Running   0          119s

    It might take several minutes for STATUS to change from Pending to Running.

Create the Redis follower Service

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

  1. The following manifest describes a Service for the Redis followers:

    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

    This manifest specifies the Service runs on port 6379. The selector field of the Service matches the Redis follower Pods created in the previous step.

    Apply the manifest to your cluster:

    kubectl apply -f redis-follower-service.yaml

  2. Verify GKE created the Service:

    kubectl get service

    The output is similar to the following:

    NAME           CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
kubernetes     10.51.240.1     <none>        443/TCP    1m
redis-leader   10.51.242.233   <none>        6379/TCP   49s
redis-follower 10.51.247.238   <none>        6379/TCP   3s

Set up the application web frontend

Now that you have Redis storage for your application, start the web servers. Like the Redis followers, the frontend is deployed using a Kubernetes Deployment.

The web application uses a PHP frontend, which 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 UI.

  1. The following manifest describes a Deployment for the web server:

    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: us-docker.pkg.dev/google-samples/containers/gke/gb-frontend:v5
        env:
        - name: GET_HOSTS_FROM
          value: "dns"
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 80

    The manifest file specifies the environment variable GET_HOSTS_FROM=dns. When you provide the configuration to the web frontend application, the frontend application uses the hostnames redis-follower and redis-leader to performs a DNS lookup. The DNS lookup finds the IP addresses of the Services you created in the previous steps. This concept is called DNS service discovery.

    Apply the manifest to your cluster:

    kubectl apply -f frontend-deployment.yaml

  2. Verify that the replicas are running:

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

    The output is similar to the following:

    NAME                        READY   STATUS    RESTARTS   AGE
frontend-7b78458576-8kp8s   1/1     Running   0          37s
frontend-7b78458576-gg86q   1/1     Running   0          37s
frontend-7b78458576-hz87g   1/1     Running   0          37s

Expose the frontend on an external IP address

With the current configuration, the redis-follower and redis-leader Services that you created in the previous steps are only accessible within the GKE cluster because the default type for a Service is ClusterIP.

A ClusterIP Service provides a single IP address for the set of Pods where the Service is pointing. This IP address is accessible only within the cluster.

To make the web frontend Service externally accessible, you can specify type: LoadBalancer or type: NodePort in the Service configuration depending on your requirements.

The following manifest describes a Service of type LoadBalancer:

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

The port declaration under the ports section specifies port: 80 and the targetPort is not specified. When you omit the targetPort property, it defaults to the value of the port field. In this case, this Service routes external traffic on port 80 to the port 80 of the containers in the frontend Deployment.

Apply the manifest to your cluster:

kubectl apply -f frontend-service.yaml

When the frontend Service is created, GKE creates a load balancer and an external IP address. These resources are subject to billing.

Visit the application website

To access the application website, get the external IP address of the frontend Service:

kubectl get service frontend

The output is similar to the following:

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

The EXTERNAL-IP column might show <pending> while the load balancer is being created. This might take several minutes. If you see errors such as Does not have minimum availability, wait a few minutes. This temporary error occurs because GKE re-creates the nodes to make the changes.

Copy the IP address and open the page in your browser:

Web application running on GKE

Try adding some 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 that you created.

Scale up the web frontend

Suppose your application has been running for a while, and it gets a sudden burst of publicity. You decide it would be a good idea to add more web servers to your frontend. You can do this by increasing the number of Pods.

  1. Scale up the number of frontend Pods:

    kubectl scale deployment frontend --replicas=5

    The output is similar to the following:

    deployment.extensions/frontend scaled

  2. Verify the number of replicas that are running:

    kubectl get pods

    The output is similar to the following:

    NAME                             READY     STATUS    RESTARTS   AGE
frontend-88237173-3s3sc          1/1       Running   0          1s
frontend-88237173-twgvn          1/1       Running   0          1s
frontend-88237173-5p257          1/1       Running   0          23m
frontend-88237173-84036          1/1       Running   0          23m
frontend-88237173-j3rvr          1/1       Running   0          23m
redis-leader-343230949-qfvrq     1/1       Running   0          54m
redis-follower-132015689-dp23k   1/1       Running   0          37m
redis-follower-132015689-xq9v0   1/1       Running   0          37m

    You can scale down the number of frontend Pods by using the same command, replacing 5 with 1.