Part 3: Docker with rails, postgres (database which is running outside the docker)

Here we are going see how docker cab be added to the existing rails application.

Files need to be created and updated

a. Dockerfile

b. docker-compose.yml

c. database.yml

Dockerfile

FROM ruby:2.4.0
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
RUN mkdir /myapp
WORKDIR /myapp
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

docker-compose.yml

version: '3'
services:
  db:
    image: postgres
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

Look for docker ip address and replace it with localhost in database.yml

example : host: 172.17.0.1

$ ifconfig

This method we are connecting to the database which is running outside the docker. So data persist.

database.yml

default: &default
  adapter: postgresql
  encoding: utf8
  pool: 5
  username: postgres
  password: enter_password
  host: 172.17.0.1


development:
  <<: *default
  database: project_db

test:
  <<: *default
  database: project_db

production:
  <<: *default
  database: project_db

If find any problem in postgres error authentication failed look here

If your postgres does not allow to connect for the ip address (ex: 172.17.0.1), then do the below listed changes

If your postgres does not allow to connect for the ip address (ex: 172.17.0.1). Then do the below listed changes

Changes to be made at two places (Path : /etc/postgresql/[version]/main/pg_hba.conf)

1.postgresql.conf

2. pg_hba.conf

1. postgresql.conf

Open the file and look for the line listern_addresses. Set it to ‘*’

For me previously it was commented and looks like

#listern_addresses = 'localhost'

Change to

 listern_addresses = '*'

2. pg_hba.conf

open the file add the host. IP address shown in the docker and additional if required. example: 172.17.0.1 in ifconfig section

host   all     all    172.17.0.0/24    md5 

All set I guess, then from project path run the below listed commands

$ docker-compose build  # Build the application

$ docker-compose up     # Start the application

hit 172.17.0.1:3000

You are done!!

$ docker-compose down   # stop the application

Rails repo can be found at here for reference

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