Example: Deploying PHP Guestbook application with MongoDB

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 MongoDB to store guestbook entries
  • Multiple web frontend instances

Objectives

  • Start up a Mongo database.
  • 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:

Your Kubernetes server must be at or later than version v1.14. To check the version, enter kubectl version.

Start up the Mongo Database

The guestbook application uses MongoDB to store its data.

Creating the Mongo Deployment

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

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo
  labels:
    app.kubernetes.io/name: mongo
    app.kubernetes.io/component: backend
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: mongo
      app.kubernetes.io/component: backend
  replicas: 1
  template:
    metadata:
      labels:
        app.kubernetes.io/name: mongo
        app.kubernetes.io/component: backend
    spec:
      containers:
      - name: mongo
        image: mongo:4.2
        args:
          - --bind_ip
          - 0.0.0.0
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 27017
  1. Launch a terminal window in the directory you downloaded the manifest files.

  2. Apply the MongoDB Deployment from the mongo-deployment.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/mongo-deployment.yaml
    
  1. Query the list of Pods to verify that the MongoDB Pod is running:

    kubectl get pods
    

    The response should be similar to this:

    NAME                            READY     STATUS    RESTARTS   AGE
    mongo-5cfd459dd4-lrcjb          1/1       Running   0          28s
    
  2. Run the following command to view the logs from the MongoDB Deployment:

    kubectl logs -f deployment/mongo
    

Creating the MongoDB Service

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

apiVersion: v1
kind: Service
metadata:
  name: mongo
  labels:
    app.kubernetes.io/name: mongo
    app.kubernetes.io/component: backend
spec:
  ports:
  - port: 27017
    targetPort: 27017
  selector:
    app.kubernetes.io/name: mongo
    app.kubernetes.io/component: backend
  1. Apply the MongoDB Service from the following mongo-service.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/mongo-service.yaml
    
  1. Query the list of Services to verify that the MongoDB 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
    mongo          ClusterIP   10.0.0.151   <none>        6379/TCP   8s
    
Note: This manifest file creates a Service named mongo with a set of labels that match the labels previously defined, so the Service routes network traffic to the MongoDB Pod.

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 mongo Service to store Guestbook entries.

Creating the Guestbook Frontend Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
  labels:
    app.kubernetes.io/name: guestbook
    app.kubernetes.io/component: frontend
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: guestbook
      app.kubernetes.io/component: frontend
  replicas: 3
  template:
    metadata:
      labels:
        app.kubernetes.io/name: guestbook
        app.kubernetes.io/component: frontend
    spec:
      containers:
      - name: guestbook
        image: paulczar/gb-frontend:v5
        # image: gcr.io/google-samples/gb-frontend:v4
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        env:
        - name: GET_HOSTS_FROM
          value: dns
        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
    
  1. Query the list of Pods to verify that the three frontend replicas are running:

    kubectl get pods -l app.kubernetes.io/name=guestbook -l app.kubernetes.io/component=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 mongo 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.

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, uncomment type: LoadBalancer.
apiVersion: v1
kind: Service
metadata:
  name: frontend
  labels:
    app.kubernetes.io/name: guestbook
    app.kubernetes.io/component: frontend
spec:
  # 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.kubernetes.io/name: guestbook
    app.kubernetes.io/component: frontend
  1. Apply the frontend Service from the frontend-service.yaml file:

    kubectl apply -f https://k8s.io/examples/application/guestbook/frontend-service.yaml
    
  1. 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   10.0.0.112   <none>       80/TCP   6s
    kubernetes     ClusterIP   10.0.0.1     <none>        443/TCP        4m
    mongo          ClusterIP   10.0.0.151   <none>        6379/TCP       2m
    

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.

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

You can scale up or down as needed 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
    mongo-1068406935-3lswp   1/1       Running   0          56m
    
  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
    mongo-1068406935-3lswp   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.kubernetes.io/name=mongo
    kubectl delete service -l app.kubernetes.io/name=mongo
    kubectl delete deployment -l app.kubernetes.io/name=guestbook
    kubectl delete service -l app.kubernetes.io/name=guestbook
    

    The responses should be:

    deployment.apps "mongo" deleted
    service "mongo" 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.
    

What's next

Last modified February 18, 2021 at 11:13 AM PST: updated labels for cli command (765e98db5)