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How to refer from one container to another using localhost – Phpmyadmin

I’m working on building docker containers for a Ruby-on-Rails project I’m currently working on, so that I can develop this project using the remote feature of Visual Studio Code. This project should still continue to work without using docker containers, so I cannot make breaking changes to the existing code that would compromise this.

The application server (Rails) needs to connect to a MySQL database that’s running in a separate container. The database container is named db, and I can connect from the application container to this container by using the db hostname.

The database.yml config file for rails defines how to connect to the database, but this is where my problem is situated. I don’t want to change the host to db instead of localhost as this would mean that regular users (that do not use Docker containers) will no longer be able to connect to the database without changing this file. How can I somehow start or change my docker config so that db is accessible as localhost instead of db inside of the application container?

database.yml:

default: &default
  adapter: mysql2
  username: ****
  password: ****
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: ****
  # setup local port forwarding for this to work
  host: db
  port: 3306

docker-compose.yml:

version: '3.7'

services:
  db:
    build: ./unipept-db
    environment:
      MYSQL_ROOT_PASSWORD: ****
      MYSQL_DATABASE: ****
      MYSQL_USER: ****
      MYSQL_PASSWORD: ****
    restart: always
    ports:
      - "3306:3306"
    hostname: mysql
  phpmyadmin:
    depends_on:
      - db
    image: phpmyadmin/phpmyadmin
    ports:
      - '8080:80'
    environment:
      PMA_HOST: db
      MYSQL_ROOT_PASSWORD: ****
    restart: always
  app:
    depends_on:
      - db
    build: ./unipept-application
    command: sleep infinity
    ports:
      - '5000:5000'
    volumes:
      - ~/.gitconfig:/root/.gitconfig
      - ..:/workspace
Tags:

2

Answers


  1. 0

    user network_mode: "host"in your APP config then you can call the DBfrom your APP using localhost:PORT

    phpmyadmin:
    depends_on:
      - db
    image: phpmyadmin/phpmyadmin
    ports:
      - '8080:80'
    environment:
      PMA_HOST: db
      MYSQL_ROOT_PASSWORD: ****
    restart: always
    network_mode: "host"
  app:
    depends_on:
      - db
    build: ./unipept-application
    command: sleep infinity
    ports:
      - '5000:5000'
    network_mode: "host"
    volumes:
      - ~/.gitconfig:/root/.gitconfig
      - ..:/workspace

    PS: Published ports are discarded when using host network mode

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  2. 0

    If you make it an environment variable in your database.yml.erb file, it will be configurable. You even already have an example of this. You can set:

    host: <%= ENV.fetch('DB_HOST', 'localhost') %>

    In development, just don’t set the environment variable, and it will use localhost. In a Docker environment, do set it, and it will use that hostname.

    version: '3'
services:
  db:
    image: mysql
  app:
    build: .
    environment:
      DB_HOST: db
    ports:
      - '5000:5000'

    You should also pass things like database credentials the same way.

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