Problem Statement

I want to create 2 databases inside one MySQL container and give the user of the first database full access to the 2nd database. With the official MySQL image one can easily create a database and allow a user access to that database. However, creating a 2nd database is not easily provisioned.

Solution

Docker images work on the concept of layers. Each new command, so to speak, creates a new layer, and herein lies our solution.

Simply create a SQL file with the following commands:

# Create second_db database if it doesn't exist
CREATE DATABASE IF NOT EXISTS second_db;
# Grant all privilidges on second_db to org_user
GRANT ALL PRIVILEGES ON second_db.* TO 'org_user' identified by 'org_user_password';

Let's say you created a file called create_second_db.sql in your project folder (or wherever you really want it to be). Then you can mount this file into docker /docker-entrypoint-initdb.d folder. Files in this folder are loaded in alphabetical order at startup time under root user.

Below is the corresponding Dockerfile (that would mount the create_second_db.sql into the /docker-entrypoint-initdb.d) folder:

# Use base mysql image with tag 5.7
FROM mysql:5.7
# Copy our custom SQL file to /docker-entrypoint-initdb.d folder
COPY ./create_second_db.sql /docker-entrypoint-initdb.d/create_second_db.sql

NOTE: You can mount as many SQL files as you would like into that folder.

Once you have created the image (via docker build), when you start the container, that container would have 2 databases created.

Build the image:

docker build -t custom_mysql -f Dockerfile .</code>

Start the container:

docker run --name custom_mysql \
-e MYSQL_ROOT_PASSWORD=my-secret-pw \
-e MYSQL_USER=org_user \
-e MYSQL_PASSWORD=org_user_password \
-e MYSQL_DATABASE=first_db \
-d custom_mysql

Result:

# rhasija ~/tmp/docker
$ docker exec -it 0fdbf85f6218 /bin/bash
root@0fdbf85f6218:/# mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.22 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| first_db           |
| mysql              |
| performance_schema |
| second_db          |
| sys                |
+--------------------+
6 rows in set (0.00 sec)

mysql>

Notice first_db and second_db above.

Boom! The job is done. Let's open the champagne!

If you have any questions, feel free to ask in the comments section.