Ggtcf

I would like to create a MySQL database using environment variables in docker-compose.yml file, but it is not working. I have the following code:

# The Database
database:
 image: mysql:5.7
 volumes:
 - dbdata:/var/lib/mysql
 restart: always
 environment:
 MYSQL_ROOT_PASSWORD: secret
 MYSQL_DATABASE: homestead
 MYSQL_USER: root
 MYSQL_PASSWORD: secret
 ports:
 - "33061:3306"

Could someone explain the function of this vars?

There is also an option to provide an init file for mysql container which will be applied each time a container is created.

database:
 image: mysql:5.7
 ports:
 - "33061:3306"
 command: --init-file /data/application/init.sql
 volumes:
 - ./init.sql:/data/application/init.sql
 environment:
 MYSQL_ROOT_USER: root
 MYSQL_ROOT_PASSWORD: secret
 MYSQL_DATABASE: homestead
 MYSQL_USER: root
 MYSQL_PASSWORD: secret

Such file could contain your initial database structure and data - for example:

CREATE DATABASE IF NOT EXISTS dev;
CREATE DATABASE IF NOT EXISTS test;
USE dev;
CREATE TABLE IF NOT EXISTS (...);

The database is probably already initialized and the configuration is stored in /var/lib/mysql. Since you defined a volume for that location the config will survive a restart. The MySQL image will not reconfigure the database over and over again, it only does this once.

volumes:
- dbdata:/var/lib/mysql

If your database is empty you can reset the database by performing docker-compose down -v where the -v removes the volumes defined in the volume section. See https://docs.docker.com/compose/reference/down/. On the next docker-compose up the MySQL image will start fresh and will initialize the database with the configuration you've provided throug the environment section.

For version 2 of docker-compose you'll .yml or .yaml can look like this:

version: '2'
volumes:
 dbdata:

services:
 mysql:
 image: mysql:5.7
 container_name: mysql
 volumes:
 - dbdata:/var/lib/mysql
 restart: always
 environment:
 - MYSQL_ROOT_PASSWORD=secret
 - MYSQL_DATABASE=homestead
 - MYSQL_USER=root
 - MYSQL_PASSWORD=secret
 ports:
 - "33061:3306"

start it with docker-compose up -d
and check:

$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a3567fb78d0d mysql:5.7 "docker-entrypoint..." 2 minutes ago Up 2 minutes 0.0.0.0:33061->3306/tcp mysql

docker exec -it a3567fb78d0d bash
root@a3567fb78d0d:/# mysql -u root -p homestead
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 7
Server version: 5.7.17 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, 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 |
| homestead |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)

Your volume will be persisted in docker volume nameoffolder_dbdata (/var/lib/docker/volumes/...)

If I understand your question correctly, you want to to have a container with a specific database in it. Like have a MySQL container with CREATE DATABASE mydb, etc. already executed. If so you need to use docker-entrypoint-initdb.d:
https://docs.docker.com/samples/library/mysql/#docker-secrets

When the official MySQL container is started for the first time, a new database will be created first. Then it will execute files with extensions .sh, .sql and .sql.gz that are found in /docker-entrypoint-initdb.d. So all you need to do is create /docker-entrypoint-initdb.d directory and put your initialisation script there.

Answering your question ...

One thing I use to do when building a new docker container is understand what the image I pull from does when is builded.

In your docker-compose.yml tou have this

# The Database
database:
 image: mysql:5.7

This is the image you pull from, "mysql:5.7"

Dockerhub is a repository where you can find info of this images.

Do a google search "mysql:5.7 dockerhub"

First result is https://hub.docker.com/_/mysql/

There you have your image 5.7, if you click on 5.7 you have this

https://github.com/docker-library/mysql/blob/607b2a65aa76adf495730b9f7e6f28f146a9f95f/5.7/Dockerfile

Which is the Dockerfile from the image, you can have a look at interesting things that happen when building the image.

One of this is ENTRYPOINT ["docker-entrypoint.sh"]

This is the file that got executed when image is ready

I you go one level up in the repo you will see this file

https://github.com/docker-library/mysql/tree/607b2a65aa76adf495730b9f7e6f28f146a9f95f/5.7

The you can see your environment variables being used to create new database etc...

file_env 'MYSQL_DATABASE'
 if [ "$MYSQL_DATABASE" ]; then
 echo "CREATE DATABASE IF NOT EXISTS `$MYSQL_DATABASE` ;" | "$mysql[@]"
 mysql+=( "$MYSQL_DATABASE" )
fi