Kubernetes + MySQL : Creating custom database and user in a Kubernetes container

I am trying to create a Django + MySQL app using Google Container Engine and Kubernetes. Following the docs from official MySQL docker image and Kubernetes docs for creating MySQL container I have created the following replication controller

apiVersion: v1
kind: ReplicationController
metadata:
  labels:
    name: mysql
  name: mysql
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: mysql
    spec:
      containers:
      - image: mysql:5.6.33
        name: mysql
        env:
          #Root password is compulsory
        - name: "MYSQL_ROOT_PASSWORD"
          value: "root_password"
        - name: "MYSQL_DATABASE"
          value: "custom_db"
        - name: "MYSQL_USER"
          value: "custom_user"
        - name: "MYSQL_PASSWORD"
          value: "custom_password"
        ports:
        - name: mysql
          containerPort: 3306
        volumeMounts:
          # This name must match the volumes.name below.
          - name: mysql-persistent-storage
            mountPath: /var/lib/mysql
      volumes:
        - name: mysql-persistent-storage
          gcePersistentDisk:
            # This disk must already exist.
            pdName: mysql-disk
            fsType: ext4

According to the docs, passing the environment variables MYSQL_DATABASE. MYSQL_USER, MYSQL_PASSWORD, a new user will be created with that password and assigned rights to the newly created database. But this does not happen. When I SSH into that container, the ROOT password is set. But neither the user, nor the database is created.

I have tested this by ruing locally and passing the same environment variables like this

docker run -d --name some-mysql 
    -e MYSQL_USER="custom_user" 
    -e MYSQL_DATABASE="custom_db" 
    -e MYSQL_ROOT_PASSWORD="root_password" 
    -e MYSQL_PASSWORD="custom_password" 
    mysql

When I SSH into that container, the database and users are created and everything works fine.

I am not sure what I am doing wrong here. Could anyone please point out my mistake. I have been at this the whole day.