docker and rails 5

Dockerfile

```ruby
FROM ruby:2.5
RUN apt-get update -qq && apt-get install -y nodejs postgresql-client
RUN mkdir /myapp
WORKDIR /myapp
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

# Add a script to be executed every time the container starts.
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]
EXPOSE 3000

# Start the main process.
CMD ["rails", "server", "-b", "0.0.0.0"]
```

Gemfile
```
source 'https://rubygems.org'
gem 'rails', '~>5
```

Gemfile.lock
touch Gemfile.lock





Next, provide an entrypoint script to fix a 
Rails-specific issue that prevents the server 
from restarting when a certain server.pid file pre-exists. 
This script will be executed every time the container 
gets started. entrypoint.sh consists of:

```
#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails.
rm -f /myapp/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile).
exec "$@"
```


docker-compose.yml
```
version: '3'
services:
  db:
    image: postgres
    environment:
        POSTGRES_DB: "db"
        POSTGRES_HOST_AUTH_METHOD: "trust"
    volumes:
      - ./tmp/db:/var/lib/postgresql/data
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db
```


docker-compose run web rails new . --force --no-deps --database=postgresql
docker-compose build



Replace the contents of config/database.yml with the following:
```
default: &default
  adapter: postgresql
  encoding: unicode
  host: db
  username: postgres
  password:
  pool: 5

development:
  <<: *default
  database: myapp_development


test:
  <<: *default
  database: myapp_test
```

docker-compose up

docker-compose run web rake db:create

docker-compose down





```
Rebuild the application
If you make changes to the Gemfile or the Compose file to try
out some different configurations, you need to rebuild. Some 
changes require only docker-compose up --build, but a full 
rebuild requires a re-run of docker-compose run web bundle 
install to sync changes in the Gemfile.lock to the host, 
followed by docker-compose up --build.

Here is an example of the first case, where a full rebuild is 
not necessary. Suppose you simply want to change the exposed 
port on the local host from 3000 in our first example to 3001. 
Make the change to the Compose file to expose port 3000 on the 
container through a new port, 3001, on the host, and save the changes:

ports: - "3001:3000"
Now, rebuild and restart the app with docker-compose up --build.

Inside the container, your app is running on the same port as before 3000, 
but the Rails Welcome is now available on http://localhost:3001 on your local host.
````


more https://docs.docker.com/compose/rails/