Docker, how to run .sql file in an image?

Question

It's my first time working with Docker an I am not sure if I am doing things well.

I have a rails applications that depends on a Mysql database, so I've configured the docker-compose.yml file like this:

db:
  image: library/mysql:5.6
  environment:
    MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
  expose:
    - "3306"
  ports:
    - "3306:3306"

rails-app:
  build: .
  dockerfile: Dockerfile
  environment:
    RAILS_ENV: development
  links:
    - db
  volumes:
    - ".:/home/app"
  volumes_from:
    - bundle

  ... omitted lines ...

Then, if I run the following:

$ docker-compose run db mysql --host=$DOCKER_LOCALHOST --port=3306 --protocol=tcp -u root < shared/create_common_tables.sql

I get this error:

ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.99.100' (111)

This sounds normal, because I suspect that I have to build before some container that links to db .

I know this because if I run this in this order:

$ docker-compose build rails-app
$ docker-compose run -e RAILS_ENV=development rails-app bundle
$ docker-compose run -e RAILS_ENV=development rails-app bundle exec rake db:create
$ docker-compose run db mysql --host=$DOCKER_LOCALHOST --port=3306 --protocol=tcp -u root < shared/create_common_tables.sql

It works fine.

But, how can I do to execute this sql before creating any container?

Answer 1

You can load the sql file during the build phase of the image. To do this you create a Dockerfile for the db service that will look something like this:

FROM mysql:5.6
COPY setup.sh /mysql/setup.sh
COPY setup.sql /mysql/setup.sql
RUN /mysql/setup.sh

where setup.sh looks something like this:

#!/bin/bash
set -e
service mysql start
mysql < /mysql/setup.sql
service mysql stop

And in your docker-compose.yml you'd change image to build: ./db or the path where you put your files.

Now this works if you have all your sql in a raw .sql file, but this wont be the case if you're using rails or a similar framework where the sql is actually stored in code. This leaves you with two options.

1. Instead of using FROM mysql:5.6 you can use FROM your_app_image_that_has_the_code_in_it and apt-get install mysql ... . This leaves you with a larger image that contains both mysql and your app, allowing you to run the ruby commands above. You'd replace the mysql < /mysql/setup/sql with the rails-app bundle exec rake db:create lines. You'd also have to provide an app config that hits a database on localhost:3306 instead of db:3306

2. My preferred option is to create a script which exports the sql into a .sql file, which you can then use to build your database container. This is a bit more work, but is a lot nicer. It means that instead of running rails-app bundle exec rake db:create you'd just run the script to load a db.

Such a script would look something like this:

#!/bin/bash
set -e
docker-compose build rails-app
docker run -d --name mysql_empty mysql:5.6
docker run --link mysql_empty:db -v $PWD:/output project_rails-app export.sh

where export.sh looks something like this:

#!/bin/bash
set -e
RAILS_ENV=development
rails-app bundle exec rake db:create
mysqldump > /output/setup.sql

You could also replace the docker run script with a second compose file if you wanted to.