Docker: Docker-compose ruby + postgres - PG::ConnectionBadcould not connect to server

Question

I created Dockerfile to ruby from official docker-compose website. I used docker compose to integrate this with Postgres. When docker-compose up, then PostgreSQL starts but I cannot connect to this. The main problem is in ruby database config because I can't change to listen to another host and set the default user. I don't know how to connect these two containers without changing the ruby database config.

Dockerfile

FROM ruby:2.3.4
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
RUN mkdir /myapp
WORKDIR /myapp
ADD Gemfile /myapp/Gemfile
ADD Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
ADD . /myapp

Docker-compose

version: '3'
services:
  db:
    image: postgres:9.6
    ports:
      - "5432:5432"
  web:
    build: .
    ports:
      - "4000:4000"
    depends_on:
      - db

Ruby database.yml

default: &default
  adapter: postgresql
  encoding: unicode
  pool: 5

development:
  <<: *default
  database: project_development

If i run inside web conatiner "bundle exec rake db:create I get error:

psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

I don't know what env set that will connect together.

Answer 1

You didn't specify database host in your database.yml. Set it to db or just try this database.yml

development: &default
  adapter: postgresql
  encoding: unicode
  database: project_development
  pool: 5
  username: postgres
  password:
  host: db

test:
  <<: *default
  database: project_test

Answer 2

You should update your database.yml with the following:

  database: ENV['DB_NAME']
  username: ENV['DB_USERNAME']
  password: ENV['DB_PASSWORD']

There's no such thing as "default PG user", so you have to create your own user with a proper permissions.

So, once you have a PG user created inside of container, you can update your docker-compose.yml file with a proper DB settings:

web:
  environment:
    - DB_NAME=rails_development
    - DB_USERNAME=rails_user
    - DB_PASSWORD=rails_password

Also, you probably want to mount local storage of postgres in your docker-compose.yml to keep data when container restarts:

volumes:
  - /var/lib/postgresql/data