docker-compose : Unable to connect Rails app to Mysql

Question

I'm trying use Docker compose and Dockerfile to connect my Ruby on Rails app to Mariadb database and importing a database (.sql file) to this database.

I'm using gem 'mysql2', '>= 0.3.18', '< 0.5'

In config/database.yml I tried:

default: &default
    adapter: mysql2
    encoding: utf8
    pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
    username: root
    password: somepassword
    host: mysql2://root:somepassword@127.0.0.1:3306/mydatabase

development:
    <<: *default

I also tried replacing the above with the following:

default: &default
    url: <%= ENV['DATABASE_URL'] %>

development:
    <<: *default

In Dockerfile I added:

# after COPY . .

RUN bundle exec rake RAILS_ENV=production DATABASE_URL=mysql2://root:somepassword@127.0.0.1:3306/mydatabase SECRET_TOKEN=sometoken assets:precompile

CMD bundle exec unicorn -c config/

In docker-compose.yml :

services:
    mysql:
        image: mariadb:10.3
        container_name: mysql
        volumes:
            - ./database.sql:/docker-entrypoint-initdb.d/database.sql
            - ~/.docker-volumes/database/mysql:/var/lib/mysql
        environment:
            MYSQL_ROOT_PASSWORD: somepassword
            MYSQL_DATABASE: mydatabase
        ports:
            - '3306:3306'

    rails_app:
        build: .
        restart: always
        container_name: rails_app
        environment:
            DATABASE_URL: mysql2://root:somepassword@mysql/mydatabase
        links:
            - mysql:sql_srv
            - redis
            - elasticsearch
        volumes:
            - .:/rails_app
         ports:
             - '3000:3000'
         env_file:
             - .rails_app.env

In .rails_app.env :

SECRET_KEY_BASE=sometoken
WORKER_PROCESSES=1
LISTEN_ON=127.0.0.1:3000
DATABASE_URL=mysql2://root:somepasssword@127.0.0.1:3306/mydatabase

The error I got for my last attempt was:

Mysql2::Error: Can't connect to MySQL server on '127.0.0.1' (111 "Connection refused")
...
ERROR: Service 'rails_app' failed to build: The command '/bin/sh -c bundle exec rake RAILS_ENV=production DATABASE_URL=mysql2://root:somepassword@127.0.0.1:3306/mydatabase SECRET_TOKEN=sometoken assets:precompile' returned a non-zero code: 1

How can I fix this issue and succeed to connect rails app with mariadb through Docker compose?

Any help please?

Answer 1

Try change database.yml to

default: &default
    adapter: mysql2
    encoding: utf8
    pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
    username: root
    password: somepassword
    host: sql_srv
    database: mydatabase
    port: 3306

Also remove DATABASE_URL from bundle exec rake in Dockerfile

You trying to connect database on 127.0.0.1 but really your DB locate on another docker container in same network, in

links:
  - mysql:sql_srv
  - redis
  - elasticsearch

you pass to rails_app service link to database service and set alias to sql_srv

From rails app you can connect to database use that link wich will be resolved in docker network to mysql service.