Deploy More Complex Microservice Apps Using PMKFT

In this tutorial we are going to expand our examples with deploying a more complex microservice. The idea is to make you more comfortable with the platform and to show you how you can leverage it for more advanced scenarios.

In this example we are going to see deployment of:

• A Redis master
• Multiple Redis slaves
• A sample guestbook application that uses Redis as a store

We assume that you have already set up a Platform9 cluster with at least one node, and the cluster is ready.

Let’s start with the Redis parts.

Deploying and exposing a Redis Cluster

Redis is a key-value in-memory store that is used mainly as a cache service. In order to set up Clustering for Data Replication we need a Redis instance that acts as Master, together with additional instances as slaves. Then the guestbook application can use this instance to store data. The Redis master will propagate the writes to the slave nodes.

We can initiate a Redis Master deployment in a few different ways: either using the kubectl tool, the Platform9 UI or the Kubernetes UI. For convenience, we use the kubectl tool as it’s the most commonly understood in tutorials.

First we need to create a Redis Cluster Deployment. Looking at their documentation here, to set up a cluster, we need some configuration properties. We can leverage kubernetes configmaps to store and reference them in the deployment spec.

We need to save a script and a redis.conf file that is going to be used to configure the master and slave nodes.

Create the following config redis-cluster.config.yml

With these values

$ cat redis-cluster.config.yml
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: redis-cluster-config
data:
  update-ip.sh: |
    #!/bin/sh
    sed -i -e "/myself/ s/[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}/${IP}/" /data/nodes.conf
    exec "$@"
  redis.conf: |+
    cluster-enabled yes
    cluster-config-file /data/nodes.conf
    appendonly yes

We define a script that will insert an IP value to the node.conf file. This is to fix an issue with Redis as referenced here. We use this script every time we deploy a new redis image.

Then we have the redis.conf, which applies the minimal cluster configuration.

Apply this spec into the cluster:

$ kubectl apply -f redis-cluster.config.yml

Then verify that it exists in the list of configmaps:

$ kubectl get configmaps

Next we need to define a spec for the redis cluster instances. We can use a Deployment or a StatefulSet to define 3 instances:

Here is the spec: redis-cluster.statefulset.yml

$ cat redis-cluster.statefulset.yml
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis-cluster
spec:
  serviceName: redis-cluster
  replicas: 6
  selector:
    matchLabels:
      app: redis-cluster
  template:
    metadata:
      labels:
        app: redis-cluster
    spec:
      containers:
      - name: redis
        image: redis:5.0.7-alpine
        ports:
        - containerPort: 6379
          name: client
        - containerPort: 16379
          name: gossip
        command: ["/conf/update-ip.sh", "redis-server", "/conf/redis.conf"]
        env:
        - name: IP
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        volumeMounts:
        - name: conf
          mountPath: /conf
          readOnly: false
        - name: data
          mountPath: /data
          readOnly: false
      volumes:
      - name: conf
        configMap:
          name: redis-cluster-config
          defaultMode: 0755
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

In the above step we defined a few things:

• An IP environment variable that we need in the update-ip.sh script that we defined in the configmap earlier. This is the pod-specific IP address using the Downward API.
• Some shared volumes including the configmap that we defined earlier.
• Two container ports – 6379 and 16379 – for the gossip protocol.

With this spec we can deploy the Redis cluster instances:

$ kubectl apply -f redis-cluster.statefulset.yml

Once we verify that we have the deployment ready, we need to perform the last step, which is bootstrapping the cluster. Consulting the documentation here for creating the cluster, we need to ssh into one of the instances and run the redis-cli cluster create command. For example taken from the docs:

$ redis-cli --cluster create 127.0.0.1:7000 127.0.0.1:7001 \
127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:7004 127.0.0.1:7005 \
--cluster-replicas 1

To do that in our case, we need to get the local pod IPs of the instances and feed them to that command.

We can query the IP using this command:

$ kubectl get pods -l app=redis-cluster -o jsonpath='{range.items[*]}{.status.podIP}:6379 '

So if we save them in a variable or a file, we can pipe them at the end of the redis-cli command:

$ POD_IPS = $(kubectl get pods -l app=redis-cluster -o jsonpath='{range.items[*]}{.status.podIP}:6379 ')

Then we can run the following command:

$ kubectl exec -it redis-cluster-0 -- redis-cli --cluster create --cluster-replicas 1 $POD_IPS

If everything is OK, you will see the following prompt. Enter ‘yes’ to accept and continue:

Can I set the above configuration? (type 'yes' to accept): yes
>>> Nodes configuration updated
>>> Assign a different config epoch to each node
>>> Sending CLUSTER MEET messages to join the cluster
Waiting for the cluster to join
........

[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.

Then we can verify the cluster state by running the cluster info command:

$ kubectl exec -it redis-cluster-0 -- redis-cli cluster info

cluster_state:ok
cluster_slots_assigned:16384
cluster_slots_ok:16384
cluster_slots_pfail:0
cluster_slots_fail:0
cluster_known_nodes:6
cluster_size:3
cluster_current_epoch:6
cluster_my_epoch:1
cluster_stats_messages_ping_sent:28
cluster_stats_messages_pong_sent:34
cluster_stats_messages_sent:62
cluster_stats_messages_ping_received:29
cluster_stats_messages_pong_received:28
cluster_stats_messages_meet_received:5
cluster_stats_messages_received:62

Before we continue deploying the guestbook app, we need to offer a unified service frontend for the Redis Cluster so that it’s easily discoverable in the cluster.

Here is the service spec: redis-cluster.service.yml

$ cat redis-cluster.service.yml

---
apiVersion: v1
kind: Service
metadata:
  name: redis-master
spec:
  type: ClusterIP
  ports:
  - port: 6379
    targetPort: 6379
    name: client
  - port: 16379
    targetPort: 16379
    name: gossip
  selector:
    app: redis-cluster

We expose the cluster as redis-master here, as the guestbook app will be looking for a host service to connect to with that name.

Once we apply this service spec, we can move on to deploying and exposing the Guestbook Application:

$ kubectl apply -f redis-cluster.service.yml

Deploying and exposing a GuestBook Application

The guestbook application is a simple php script that shows a form to submit a message. Initially it will attempt to connect to either the redis-masterhost or the redis-slave hosts. It needs the GET_HOSTS_FROM environment variable set pointing to the file with the following variables: REDIS_MASTER_SERVICE_HOST: of the master REDIS_SLAVE_SERVICE_HOST: of the slave

First, let’s define the deployment spec bellow:

php-guestbook.deployment.yml

$ cat php-guestbook.deployment.yml

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: guestbook
spec:
  replicas: 1
  selector:
    matchLabels:
      app: guestbook
  template:
    metadata:
      labels:
        app: guestbook
    spec:
      containers:
      - name: php-redis
        image: gcr.io/google-samples/gb-frontend:v6
        resources:
          requests:
            cpu: 150m
            memory: 150Mi
        env:
        - name: GET_HOSTS_FROM
          value: env
        - name: REDIS_MASTER_SERVICE_HOST
          value: "redis-master"
        - name: REDIS_SLAVE_SERVICE_HOST
          value: "redis-master"
        ports:
        - containerPort: 80

The code of the gb-frontend image is located here.

Next is the the associated service spec:

---
apiVersion: v1
kind: Service
metadata:
  name: guestbook-lb
spec:
  type: NodePort
  ports:
  - port: 80
  selector:
      app: guestbook

Note: NodePort will assign a random port over the public IP of the Node. In either case, we get a public host:port pair where we can inspect the application. Here is a screenshot of the app after we deployed it:

Cleaning up

Once we have finished experimenting with the application, we can clean up the resources and all the servers by issuing kubectl delete statements. A convenient way is to delete by labels. For example:

$ kubectl delete statefulset redis-cluster
$ kubectl delete service redis-master
$ kubectl delete deployment guestbook
$ kubectl delete service guestbook-lb
$ kubectl delete configmap redis-cluster-config
$ kubectl delete pvc -l app=redis-cluster

Next Steps

Deploying multi-container systems in Kubernetes with Platform9 is no different than usual. The big difference is that you gain a quality of server and a maintenance-free Kubernetes experience with first-class support for troubleshooting issues. That’s not to mention that you can host the cluster on your own bare-metal server or AWS, eliminating any vendor lock-ins. For more information visit Platform9 Managed Kubernetes page.