Deploying and scaling an Oracle database on a multi-node Kubernetes cluster

In this post I am going to explain how to deploy and scale a Oracle Express database on a multi-node Kubernetes cluster. I am going to use this Docker container by Maxym Bylenko.  I am referring to the container for the Oracle XE 11g because of the following open issue with that for Oracle XE 12c at the time I did the process described below. I am assuming the readers have at least basic or middle level knowledge of the Kubernetes concepts.
First thing to do is to create a Pod. We can do this (and other operations described in this post) declaratively through a YAML file:

apiVersion: v1
kind: Pod
metadata:
  name: "oradb"
labels:
  name: "oradb"
spec:
    containers:
      - image: "sath89/oracle-xe-11g:latest"
        name: "oradb"
        ports:
          - containerPort: 1521
        restartPolicy: Always

Once the Pod has been successfully created, we need to create a Service for it:

apiVersion: v1
kind: Service
metadata:
  name: "oradb"
  labels:
    app: "oradb"
spec:
  ports:
    - port: 1521
  selector:
    app: "oradb"

Now we need to create a ReplicationController. It enables to easily create multiple pods and then ensure that that number of pods always exists: if a pod crashes, the Replication Controller replaces it. Here's how we can declaratively create a ReplicationController, specifying we want 2 replicas:

apiVersion: v1
kind: ReplicationController
metadata:
  name: "oradb"
  labels:
    app: "oradb"
spec:
  replicas: 2
  selector:
    app: "oradb"
  template:
    metadata:
      labels:
        app: "oradb"
    spec:
      containers:
        - image: "sath89/oracle-xe-11g:latest"
          name: "oradb"

We can check if the ReplicationController has been created successfully from a shell through kubectl:

kubectl get rc

or, if in OpenShift Origin:

oc get rc

NAME      DESIRED   CURRENT   AGE
oradb       2            2                  1d

Let's check for the pods:

kubectl get pods

or, in OpenShift Origin:

oc get pods

NAME          READY     STATUS    RESTARTS   AGE
oradb           1/1         Running        0          1d
oradb-6rs8h   1/1       Running        0          1d
oradb-cq2x9   1/1       Running       0          1d

Imagine now we need to scale the cluster from 2 to 3 Pods. It is possible to do this simply with the kubectl scale command:

kubectl scale rc oradb --replicas=3

or the oc scale command:
 
oc scale rc oradb --replicas=3

As soon as the command above has been completed, we would find a new pod in the list:

NAME          READY     STATUS    RESTARTS   AGE
oradb           1/1         Running        0          1d
oradb-6rs8h   1/1       Running        0          1d
oradb-cq2x9   1/1       Running       0          1d
oradb-rplzj   1/1       Running       0          1d
 
And that's the new situation for the ReplicationController:

NAME      DESIRED   CURRENT   AGE
oradb       3            3                  1d

The database sid is xe and the credentials to connect are:
username: system
password: oracle