Rails-Postgres-on-Docker

This is a rails demo app that links to postgres and running on docker

Prerequisites

Step 1 - Setting and starting a new rails app

Open your terminal and run

	rails new [your_app_name]

Then,

	rails server

Once successful, open up your browser and go to localhost:3000 or the port that you've allocated to the rails server.

You'll be able to see a rails welcome page.

For kali users, you may run into problems because of its 'incompatibility' with ruby. You'll have to reinstall it using rvm and not directly with apt-get. More here

Step 2 - Dockerizing your rails app

Navigate to the root of your rails app. Then in the terminal,

	touch Dockerfile

This will create an empty dockerfile. Visit the link above on What and why docker for more on Dockerfile.

Open the newly created Dockerfile with your favorite editor, I use sublime. Then, copy the following:

FROM ruby:2.5.1
MAINTAINER your_name
RUN apt-get update && apt-get install -y build-essential && apt-get install -y nodejs
WORKDIR /
COPY Gemfile /
COPY Gemfile.lock /
RUN gem install bundler && bundle install
COPY . ./
EXPOSE 3000
ENTRYPOINT ["bundle", "exec"]
CMD ["rails","server","-b","0.0.0.0"]

Save it and run:

	docker build -t [tagname] .

This will build your image from the Dockerfile. At this point, you can actually run the docker image and view it on your browser with:

	docker run -p your_image_name

If you are having problems with port problems, in your terminal,

	docker ps

This will list your running images. Use the port of your corresponding image

docker-compose

Let's introduce docker-compose. More here.

Inside your rails app root directory, create a new file called docker-compose.yml. In it paste the following:

	version: "3"
		services: 
  			web:
    			build: .
    			command: rails server -p 3000 -b '0.0.0.0'
    			volumes:
                 - .:/myapp
    			ports:
                 - 3000:3000
    			links:
                 - db
  			db:
    			image: postgres
			    ports:
                 - "5432"

Don't build the container yet but you are free to do so.

Setup Postgresql

Open up Gemfile and include gem 'pg'. You can delete gem 'sqlite3' because we won't be using sqlite for our database needs.

Then, open config/database.yml and replace its content with the following:

default: &default
  adapter: postgresql
  pool: 5
  timeout: 5000
  username: postgres
  host: db
  port: 5432

development:
  <<: *default
  database: myapp_db

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: myapp_db_test

production:
  <<: *default
  database: myapp_db_prod

You can now build your container with

	docker-compose build

If you, start your container at this point, you'll stumble into issues with the app connecting to a non existing database. To solve this:

	docker-compose run web rake db:create

web is the name of the service as defined in the docker-compose.yml file.

Once successful, you can now do:

	docker-compose up

to start your application.

Yay, you've just dockerized your application!