Wordpress

Next we'll setup Wordpress that requires MySQL and persisted volume.

In https://hub.docker.com/_/wordpress/ there is a massive list of different variants in Supported tags and respective Dockerfile links - most likely for this testing we can use any of the images. From "How to use this image" we can see that all variants require WORDPRESS_DB_HOST that needs to be MySQL.So before moving forward, let's setup that.

In https://hub.docker.com/_/mysql/ there's a sample compose file under "via docker stack deploy or docker-compose" - Let's strip that down to

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example

Under "Caveats - Where to Store Data" we can see that the /var/lib/mysql needs to be mounted separately to preserve data so that the container can be recreated.

First, let's try with bind mount:

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - ./mysql-data:/var/lib/mysql

And now docker compose up

Then, with a volume

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - mysql-data:/var/lib/mysql

volumes:
  mysql-data:

And then docker-compose up

Now when the MySQL is running, let's add the actual Wordpress. The container seems to require just two environment variables.

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - mysql-data:/var/lib/mysql
  wordpress:
    image: 'wordpress:4.9.1-php7.1-apache'
    environment:
      - WORDPRESS_DB_HOST=db
      - WORDPRESS_DB_PASSWORD=example
    ports:
      - '9999:80'
    depends_on:
      - db

volumes:
  mysql-data:

We also declare that db service should be started first and that the container will link to it - The MySQL server is accessible with dns name "db" from the Wordpress service.

Now when you run, we'll find that it doesn't work:

$ docker compose up
...
MySQL Connection Error: (2054) The server requested authentication method unknown to the client

We need to start mysql with --default-authentication-plugin=mysql_native_password to enable plain text passwords:

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    command: --default-authentication-plugin=mysql_native_password
    volumes:
      - mysql-data:/var/lib/mysql

  wordpress:
    image: 'wordpress:4.9.1-php7.1-apache'
    environment:
      - WORDPRESS_DB_HOST=db
      - WORDPRESS_DB_PASSWORD=example
    ports:
      - '9999:80'
    depends_on:
      - db

volumes:
  mysql-data:

Then we need to delete the volume, because the setting is persisted there:

docker compose down -v

And now, we'll run again:

docker compose up

From the wordpress logs we'll see that:

$ docker compose logs wordpress
...
wordpress_1  | WordPress not found in /var/www/html - copying now...
wordpress_1  | Complete! WordPress has been successfully copied to /var/www/html
...

Wordpress image creates files in startup at /var/www/html that also needs to be persisted. The Dockerfile has this line https://github.com/docker-library/wordpress/blob/6a085d90853b8baffadbd3f0a41d6814a2513c11/php7.1/apache/Dockerfile#L44 where it declares that a volume should be created. Docker will create the volume, but it will be handled as a anonymous volume that is not managed by compose, so it's better to be explicit about the volume. With that in mind our final file should look like this:

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    command: --default-authentication-plugin=mysql_native_password
    volumes:
      - mysql-data:/var/lib/mysql

  wordpress:
    image: 'wordpress:4.9.1-php7.1-apache'
    environment:
      - WORDPRESS_DB_HOST=db
      - WORDPRESS_DB_PASSWORD=example
    ports:
      - '9999:80'
    depends_on:
      - db
    volumes:
      - wordpress-data:/var/www/html

volumes:
  mysql-data:
  wordpress-data:

Now open and configure the installation at http://localhost:9999

We can inspect the changes that happened in the image and ensure that no extra meaningful files got written to the container:

$ docker compose ps
  NAME                    COMMAND                  SERVICE             STATUS              PORTS
  wordpress-db-1          "docker-entrypoint.s…"   db                  running             33060/tcp
  wordpress-wordpress-1   "docker-entrypoint.s…"   wordpress           running             0.0.0.0:9999->80/tcp

$ docker diff wordpress-wordpress-1
  C /run
  C /run/apache2
  A /run/apache2/apache2.pid

Run "at" wordpress.colasloth.com with

version: '3'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    command: --default-authentication-plugin=mysql_native_password
    volumes:
      - mysql-data:/var/lib/mysql

  wordpress:
    image: 'wordpress:4.9.1-php7.1-apache'
    environment:
      - WORDPRESS_DB_HOST=db
      - WORDPRESS_DB_PASSWORD=example
      - VIRTUAL_HOST=wordpress.colasloth.com
    depends_on:
      - db
    volumes:
      - wordpress-data:/var/www/html

  proxy:
    image: jwilder/nginx-proxy
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock:ro
    ports:
      - 80:80

volumes:
  mysql-data:
  wordpress-data:

You have reached the end of this section!