Prerequisites

Parse uses MongoDB cluster for its storage. Chapter 13 described how to set up a replicated MongoDB using Kubernetes StatefulSets. This section assumes you have a three-replica Mongo cluster running in Kubernetes with the names mongo-0.mongo, mongo-1.mongo, and mongo-2.mongo.

These instructions also assume that you have a Docker login; if you don’t have one, you can get one for free at https://docker.com.

Finally, we assume you have a Kubernetes cluster deployed and the kubectl tool properly configured.

Building the parse-server

The open source parse-server comes with a Dockerfile by default, for easy containerization. First, clone the Parse repository:

$ git clone https://github.com/ParsePlatform/parse-server

Then move into that directory and build the image:

$ cd parse-server
$ docker build -t ${DOCKER_USER}/parse-server .

Finally, push that image up to the Docker hub:

$ docker push ${DOCKER_USER}/parse-server

Deploying the parse-server

Once you have the container image built, deploying the parse-server into your cluster is fairly straightforward. Parse looks for three environment variables when being configured:

APPLICATION_ID

An identifier for authorizing your application

MASTER_KEY

An identifier that authorizes the master (root) user

DATABASE_URI

The URI for your MongoDB cluster

Putting this all together, you can deploy Parse as a Kubernetes Deployment using the YAML file in Example 14-1.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: parse-server
  namespace: default
spec:
  replicas: 1
  template:
    metadata:
      labels:
        run: parse-server
    spec:
      containers:
      - name: parse-server
        image: ${DOCKER_USER}/parse-server
        env:
        - name: DATABASE_URI
          value: "mongodb://mongo-0.mongo:27017,\
            mongo-1.mongo:27017,mongo-2.mongo\
            :27017/dev?replicaSet=rs0"
        - name: APP_ID
          value: my-app-id
        - name: MASTER_KEY
          value: my-master-key

Testing Parse

To test your deployment, you need to expose it as a Kubernetes service. You can do that using the service definition in Example 14-2.

apiVersion: v1
kind: Service
metadata:
  name: parse-server
  namespace: default
spec:
  ports:
  - port: 1337
    protocol: TCP
    targetPort: 1337
  selector:
    run: parse-server

Now your Parse server is up and running and ready to receive requests from your mobile applications. Of course, in any real application you are likely going to want to secure the connection with HTTPS. You can see the parse-server GitHub page for more details on such a configuration.

Configuring Ghost

Ghost is configured with a simple JavaScript file that describes the server. We will store this file as a configuration map. A simple development configuration for Ghost looks like Example 14-3.

var path = require('path'),
    config;

config = {
    development: {
        url: 'http://localhost:2368',
        database: {
            client: 'sqlite3',
            connection: {
                filename: path.join(process.env.GHOST_CONTENT,
                                    '/data/ghost-dev.db')
            },
            debug: false
        },
        server: {
            host: '0.0.0.0',
            port: '2368'
        },
        paths: {
            contentPath: path.join(process.env.GHOST_CONTENT, '/')
        }
    }
};

module.exports = config;

Once you have this configuration file saved to ghost-config.js, you can create a Kubernetes ConfigMap object using:

$ kubectl create cm --from-file ghost-config.js ghost-config

This creates a ConfigMap that is named ghost-config. As with the Parse example, we will mount this configuration file as a volume inside of our container. We will deploy Ghost as a Deployment object, which defines this volume mount as part of the Pod template (Example 14-4).

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: ghost
spec:
  replicas: 1
  selector:
    matchLabels:
      run: ghost
  template:
    metadata:
      labels:
        run: ghost
    spec:
      containers:
      - image: ghost
        name: ghost
        command:
        - sh
        - -c
        - cp /ghost-config/ghost-config.js /var/lib/ghost/config.js
          && /usr/local/bin/docker-entrypoint.sh node current/index.js
        volumeMounts:
        - mountPath: /ghost-config
          name: config
      volumes:
      - name: config
        configMap:
          defaultMode: 420
          name: ghost-config

One thing to note here is that we are copying the config.js file from a different location into the location where Ghost expects to find it, since the ConfigMap can only mount directories, not individual files. Ghost expects other files that are not in that ConfigMap to be present in its directory, and thus we cannot simply mount the entire ConfigMap into /var/lib/ghost.

You can run this with:

$ kubectl apply -f ghost.yaml

Once the pod is up and running, you can expose it as a service with:

$ kubectl expose deployments ghost --port=2368

Once the service is exposed, you can use the kubectl proxy command to access the Ghost server:

$ kubectl proxy

Then visit http://localhost:8001/api/v1/namespaces/default/services/ghost/proxy/ in your web browser to begin interacting with Ghost.

...
database: {
   client: 'mysql',
   connection: {
     host     : 'mysql',
     user     : 'root',
     password : 'root',
     database : 'ghost_db',
     charset  : 'utf8'
   }
 },
...

$ kubectl create configmap ghost-config-mysql --from-file ghost-config.js

...
      - configMap:
          name: ghost-config-mysql
...

$ kubectl exec -it mysql-zzmlw -- mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
...

mysql> create database ghost_db;
...

$ kubectl apply -f ghost.yaml

$ kubectl apply -f ghost.yaml

Configuring Redis

As before, we’re going to use Kubernetes ConfigMaps to configure our Redis installation. Redis needs separate configurations for the master and slave replicas. To configure the master, create a file named master.conf that contains the code in Example 14-5.

bind 0.0.0.0
port 6379

dir /redis-data

This directs Redis to bind to all network interfaces on port 6379 (the default Redis port) and store its files in the /redis-data directory.

The slave configuration is identical, but it adds a single slaveof directive. Create a file named slave.conf that contains what’s in Example 14-6.

bind 0.0.0.0
port 6379

dir .

slaveof redis-0.redis 6379

Notice that we are using redis-0.redis for the name of the master. We will set up this name using a service and a StatefulSet.

We also need a configuration for the Redis sentinel. Create a file named sentinel.conf with the contents of Example 14-7.

bind 0.0.0.0
port 26379

sentinel monitor redis redis-0.redis 6379 2
sentinel parallel-syncs redis 1
sentinel down-after-milliseconds redis 10000
sentinel failover-timeout redis 20000

Now that we have all of our configuration files, we need to create a couple of simple wrapper scripts to use in our StatefulSet deployment.

The first script simply looks at the hostname for the Pod and determines whether this is the master or a slave, and launches Redis with the appropriate configuration. Create a file named init.sh containing the code in Example 14-8.

#!/bin/bash
if [[ ${HOSTNAME} == 'redis-0' ]]; then
  redis-server /redis-config/master.conf
else
  redis-server /redis-config/slave.conf
fi

The other script is for the sentinel. In this case it is necessary because we need to wait for the redis-0.redis DNS name to become available. Create a script named sentinel.sh containing the code in Example 14-9.

#!/bin/bash
while ! ping -c 1 redis-0.redis; do
  echo 'Waiting for server'
  sleep 1
done

redis-sentinel /redis-config/sentinel.conf

Now we need to package all of these files up into a ConfigMap object. You can do this with a single command line:

$ kubectl create configmap \
  --from-file=slave.conf=./slave.conf \
  --from-file=master.conf=./master.conf \
  --from-file=sentinel.conf=./sentinel.conf \
  --from-file=init.sh=./init.sh \
  --from-file=sentinel.sh=./sentinel.sh \
  redis-config

Creating a Redis Service

The next step in deploying Redis is to create a Kubernetes service that will provide naming and discovery for the Redis replicas (e.g., redis-0.redis). To do this, we create a service without a cluster IP address (Example 14-10).

apiVersion: v1
kind: Service
metadata:
  name: redis
spec:
  ports:
  - port: 6379
    name: peer
  clusterIP: None
  selector:
    app: redis

You can create this service with kubectl apply -f redis-service.yaml. Don’t worry that the Pods for the service don’t exist yet. Kubernetes doesn’t care; it will add the right names when the Pods are created.

Deploying Redis

We’re ready to deploy our Redis cluster. To do this we’re going to use a StatefulSet. We introduced StatefulSets in “Manually Replicated MongoDB with StatefulSets”, when we discussed our MongoDB installation. StatefulSets provide indexing (e.g., redis-0.redis) as well as ordered creation and deletion semantics (redis-0 will always be created before redis-1, and so on). They’re quite useful for stateful applications like Redis, but honestly, they basically look like Kubernetes Deployments. For our Redis cluster, here’s what the StatefulSet looks like Example 14-11.

apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
  name: redis
spec:
  replicas: 3
  serviceName: redis
  template:
    metadata:
      labels:
        app: redis
    spec:
      containers:
      - command: [sh, -c, source /redis-config/init.sh ]
        image: redis:3.2.7-alpine
        name: redis
        ports:
        - containerPort: 6379
          name: redis
        volumeMounts:
        - mountPath: /redis-config
          name: config
        - mountPath: /redis-data
          name: data
      - command: [sh, -c, source /redis-config/sentinel.sh]
        image: redis:3.2.7-alpine
        name: sentinel
        volumeMounts:
        - mountPath: /redis-config
          name: config
      volumes:
      - configMap:
          defaultMode: 420
          name: redis-config
        name: config
      - emptyDir:
        name: data

You can see that there are two containers in this Pod. One runs the init.sh script that we created and the main Redis server, and the other is the sentinel that monitors the servers.

You can also note that there are two volumes defined in the Pod. One is the volume that uses our ConfigMap to configure the two Redis applications, and the other is a simple emptyDir volume that is mapped into the Redis server container to hold the application data so that it survives a container restart. For a more reliable Redis installation this could be a network-attached disk, as discussed in Chapter 13.

Now that we’ve defined our Redis cluster, we can create it using:

$ kubectl apply -f redis.yaml

Playing with Our Redis Cluster

To demonstrate that we’ve actually successfully created a Redis cluster, we can perform some tests.

First, we can determine which server the Redis sentinel believes is the master. To do this, we can run the redis-cli command in one of the pods:

$ kubectl exec redis-2 -c redis \
  -- redis-cli -p 26379 sentinel get-master-addr-by-name redis

This should print out the IP address of the redis-0 pod. You can confirm this using kubectl get pods -o wide.

Next, we’ll confirm that the replication is actually working.

To do this, first try to read the value foo from one of the replicas:

$ kubectl exec redis-2 -c redis -- redis-cli -p 6379 get foo

You should see no data in the response.

Next, try to write that data to a replica:

$ kubectl exec redis-2 -c redis -- redis-cli -p 6379 set foo 10
READONLY You can't write against a read only slave.

You can’t write to a replica, because it’s read-only. Let’s try the same command against redis-0, which is the master:

$ kubectl exec redis-0 -c redis -- redis-cli -p 6379 set foo 10
OK

Now try the original read from a replica:

$ kubectl exec redis-2 -c redis -- redis-cli -p 6379 get foo
10

This shows that our cluster is set up correctly, and data is replicating between masters and slaves.