Docker volumes MariaDB Windows

Question

I am trying to Dockerize and Open Source a project I created in second year of college, this project uses MariaDB, phpMyAdmin and PHP/Yii Framework.

My objective is to make it ready to go using only a simple docker-compose up command.

I managed to get the connection between phpMyAdmin and the DB working and now I am stuck on trying to get Docker to have a relative path to a database volume, to make it consistent.

Here is what I have regarding the volume mounting:

volumes:
  - './database/mysql/:/var/lib/mysql'

This is storing the database files inside the project and then I can ignore those files in .gitignore The problem is when I run docker-compose up with this configuration I get:

Invalid volume specification: 'C:\Users\MySelf\coding\my_app\database\mysql:/var/lib/mysql:rw'

Regarding the host, I am using a Windows with Docker Toolbox but I want the docker-compose.yml to work regardless of the OS.

I have seen other questions similar but their error came from problems with absolute paths on Windows which I am not looking for.

EDIT: Adding the correct final docker-compose.yml, hopefully it can help

version: '2'
services:
  web_db:
    build: ./database/mysql
    command: "mysqld --innodb-buffer-pool-size=20M"
    volumes:
      - ./database/mysql/data/:/var/lib/mysql
      - ./database/mysql/initDB/create_tables.sql:/docker-entrypoint-initdb.d/create_tables.sql
    environment:
      MYSQL_ROOT_PASSWORD: 'YOURPASSWORD'
      MYSQL_DATABASE: 'support-technique'
      MYSQL_ROOT_HOST: '172.17.0.1'
    ports:
      - "3306:3306"
    container_name: web_db

  web:
    build: .
    depends_on:
      - web_db
    links:
      - web_db:db
    ports:
      - "80:80"

  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    depends_on:
      - web_db
    links:
      - web_db:mysql
    ports:
      - "8181:80"
    environment:
PMA_HOST: mysql

Answer 1

When you Mount a host directory as a data volume, the documentation says:

The host-dir can either be an absolute path or a name value. If you supply an absolute path for the host-dir, Docker bind-mounts to the path you specify. If you supply a name, Docker creates a named volume by that name.

A name value must start with an alphanumeric character, followed by a-z0-9, _ (underscore), . (period) or - (hyphen).
An absolute path starts with a / (forward slash).

That explain the error message.

Using an absolute path links it to the OS (which is not what you want)

docker run -v c:\<path>:/c:\<container path>
docker run -v /c/<path>:/c:\<container path>

As mentioned in "Running a docker-compose “Getting Started” example causes “Invalid volume specification” on Windows", try first setting this docker-compose environment variable:

Create .env file in the path docker-compose.yml is placed with following content:

COMPOSE_CONVERT_WINDOWS_PATHS=1

The OP Daniel confirms in the comments that with the .env including COMPOSE_CONVERT_WINDOWS_PATHS, a relative path works.

I would recommend using a data volume name instead: it won't depend on an host pathname.