# Create basic Rails App with Docker

## Generating App Skeleton

inside the container, install rails and generate application with some predefined configuration

```sh
$ docker run --rm -v $PWD:/usr/src -w /usr/src ruby:2.3.3 bash
$ gem install rails
$ rails new "AppName" --database postgresql --skip-bundle
```

### Configuration files for the docker environment
- now, exit the container and enter the project directory
- create your Dockerfile, docker-compose.yml, .dockerignore and .env files

## Dockerfile
```Dockerfile
FROM ruby:2.3.3

# Set TERM env to avoid error message "TERM environment variable not set"
ENV TERM=xterm

RUN apt-get update -yqq \
  && apt-get install -yqq --no-install-recommends \
    postgresql-client \
    nodejs \
  && apt-get -q clean \
  && rm -rf /var/lib/apt/lists

# Pre-install gems with native extensions
RUN gem install nokogiri -v "1.6.8.1"

WORKDIR /usr/src/app
COPY Gemfile* ./
RUN bundle install
COPY . .

CMD rails server -b 0.0.0.0
```

## docker-compose.yml
```yml
version: "2"

volumes:
  db-data:
    external: false

services:
  db:
    image: postgres
    env_file: .env
    volumes:
      - db-data:/var/lib/postgresql/db-data

  app:
    build: .
    env_file: .env
    volumes:
      - .:/usr/src/app
    ports:
      - "3000:3000"
    depends_on:
      - db
```

## .dockerignore
```.dockerignore
.git
.gitignore
README.md

Dockerfile
docker-compose.yml
.dockerignore

log/*
tmp/*
.rake_tasks*
```

## .env
```dotfile
POSTGRES_USER=postgres
POSTGRES_PASSWORD=pass1234
```

## Gemfile
- add Nokogiri in Gemfile, that will speed up image build time

```Gemfile
gem 'nokogiri', '~> 1.6', '>= 1.6.8.1'
```

## database.yml
```yml
default: &default
  adapter: postgresql
  encoding: unicode
  host: db
  username: <%= ENV["POSTGRES_USER"] %>
  password: <%= ENV["POSTGRES_PASSWORD"] %>
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: "name_db"_development

test:
  <<: *default
  database: "name_db"_test

production:
  <<: *default
  host: <%= ENV["POSTGRES_HOST"] %>
  database: "name_db"_production
```

### build image and generate database
```sh
$ docker-compose build
$ docker-compose run --rm app rake db:create db:migrate
```

### run containers in the background
```sh
$ docker-compose up -d
```
### run the bundle command on a container that is running
```sh
$ docker-compose exec app <rails command>
```

#### tips
- after adding a gem in Gemfile, run the build again

```sh
$ docker-compose build
```