Starting docker in rails 7.1 with a separate MySQL container

docker-in-rails-7-with-mysql.md

Setting Up MySQL

1. Pull the MySQL image:

   docker pull mysql/mysql-server

2. Run the MySQL container in a persistent volume:

   docker run --rm -d \
     --name=mysql_container \
     -p 3307:3306 \
     -e MYSQL_ROOT_PASSWORD=password \
     -e MYSQL_ROOT_HOST=% \
     -v mysql-data:/var/lib/mysql \
     mysql/mysql-server
   

   • Explanation:
     • --rm: Remove the container when it stops.
     • -d: Run the container in the background.
     • --name=mysql_container: Name the container for easier management.
     • -p 3307:3306: Map the container port 3306 (MySQL) to host port 3307.
     • -e MYSQL_ROOT_PASSWORD=password: Set the root password for the MySQL user.
     • -e MYSQL_ROOT_HOST=%: Allow connections from any host.
     • -v mysql-data:/var/lib/mysql: Mounts the volume (mysql-data) to the container's /var/lib/mysql directory (where MySQL stores data).
     • mysql/mysql-server: Specifies the Docker image for the MySQL server.

3. Get the container's IP Address:

   docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' mysql_container

   This will display the container's IP address, which will be used later.

4. Set environment variables:

   export DATABASE_URL='mysql2://root:password@<container_ip>/<db_name>:3306?encoding=utf8mb4'
   export RAILS_MASTER_KEY=<rails_master_key>

   • Replace <container_ip> with the IP address obtained in the previous step.
   • Replace <db_name> with the name of the database you want to use.
   • Replace <rails_master_key> with the master key from config/master.key.

Running project

1. Build the project image:

   docker-compose build -t <rails_app> .

   • Replace <rails_app> with the name you want to give to the image.
   • This will build the image using the Dockerfile.

2. Run the project container:

   docker run --rm -it -p 3000:3000 --name=<rails_app_container> \
     -e DATABASE_URL=$DATABASE_URL \
     -e RAILS_MASTER_KEY=$RAILS_MASTER_KEY \
     <rails_app>

   • Replace <rails_app_container> with the name you want to give to the container.
   • Replace <rails_app> with the name of the image you built in the previous step.
   • Explanation:
     • --rm: Remove the container when it stops.
     • -it: Run in interactive.
     • -p 3000:3000: Map the container port 3000 (Rails) to host port 3000.
     • -e DATABASE_URL=$DATABASE_URL: Set the database URL environment variable.
     • -e RAILS_MASTER_KEY=$RAILS_MASTER_KEY: Set the Rails master key environment variable.

Debugging

• View MySQL container logs:

  docker logs mysql_container

• Enter the MySQL container:

  docker exec -it mysql_container bash

  • This will open a bash shell inside the container.
  • You can then run mysql -u root -p to enter the MySQL command line.
  • Use exit to leave the container.

Controlling the MySQL container

• Stop the container:

  docker stop mysql_container

• Start the container:

  docker start mysql_container

• Remove the container:

  docker rm mysql_container