Base Rails Docker Development Environment

database.yml

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS", 5) %>
  username: <%= ENV.fetch("DATABASE_USER", 'postgres') %>
  host: <%= ENV.fetch("DATABASE_HOST", 'localhost') %>
  port: 5432

development:
  <<: *default
  database: docker_development
test:
  <<: *default
  database: docker_test

production:
  <<: *default
  database: docker_production
  username: docker
  password: <%= ENV['DOCKER_DATABASE_PASSWORD'] %>

docker-compose.yml

version: '3.7'

services:
  rails:
    build:
      context: ./docker/ruby
      args:
        - RUBY_VERSION=2.6.5
        - BUNDLE_JOBS=15
        - BUNDLE_RETRY=2
        - NODE_VERSION=12
        - INSTALL_PG_CLIENT=true
        - UID=500
        - GID=500
    environment:
      - DATABASE_USER=postgres
      - DATABASE_HOST=postgres
    command: bundle exec rails server -p 3000 -b '0.0.0.0'
    entrypoint: docker/ruby/entrypoint.sh
    volumes:
      - .:/app:cached
      - gems:/gems
      - node_modules:/app/node_modules
      - packs:/app/public/packs
      - rails_cache:/app/tmp/cache
    ports: 
      - "3000:3000"
    user: ruby
    tty: true
    stdin_open: true
    depends_on:
      - postgres
  postgres:
    image: postgres:11
    environment:
      - POSTGRES_HOST_AUTH_METHOD=trust
    volumes:
      - postgres:/var/lib/postgresql/data

volumes:
  gems:
  postgres:
  node_modules:
  packs:
  rails_cache:

Dockerfile

ARG RUBY_VERSION=2.6
FROM ruby:$RUBY_VERSION

ARG DEBIAN_FRONTEND=noninteractive

ARG NODE_VERSION=11
RUN curl -sL https://deb.nodesource.com/setup_$NODE_VERSION.x | bash -
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
  echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list

RUN apt-get update && apt-get install -y \
  build-essential \
  nodejs \
  yarn \
  locales \
  git \
  netcat \
  vim \
  sudo
  
ARG UID
ENV UID $UID
ARG GID
ENV GID $GID
ARG USER=ruby
ENV USER $USER

RUN groupadd -g $GID $USER && \
    useradd -u $UID -g $USER -m $USER && \
    usermod -p "*" $USER && \
    usermod -aG sudo $USER && \
    echo "$USER ALL=NOPASSWD: ALL" >> /etc/sudoers.d/50-$USER

ENV LANG C.UTF-8

ENV BUNDLE_PATH /gems
ENV BUNDLE_HOME /gems

ARG BUNDLE_JOBS=20
ENV BUNDLE_JOBS $BUNDLE_JOBS

ARG BUNDLE_RETRY=5
ENV BUNDLE_RETRY $BUNDLE_RETRY

ENV GEM_HOME /gems
ENV GEM_PATH /gems

ENV PATH /gems/bin:$PATH

ARG INSTALL_PG_CLIENT=false
RUN if [ "$INSTALL_PG_CLIENT" = true ]; then \
    apt-get install -y postgresql-client \
;fi

RUN mkdir -p "$GEM_HOME" && chown $USER:$USER "$GEM_HOME"
RUN mkdir -p /app && chown $USER:$USER /app

WORKDIR /app

RUN mkdir -p node_modules && chown $USER:$USER node_modules
RUN mkdir -p public/packs && chown $USER:$USER public/packs
RUN mkdir -p tmp/cache && chown $USER:$USER tmp/cache

USER $USER

RUN gem install bundler

entrypoint.sh

#! /bin/bash
set -e

: ${APP_PATH:="/app"}
: ${APP_TEMP_PATH:="$APP_PATH/tmp"}
: ${APP_SETUP_LOCK:="$APP_TEMP_PATH/setup.lock"}
: ${APP_SETUP_WAIT:="5"}

# 1: Define the functions to lock and unlock our app container's setup
# processes:
function lock_setup { mkdir -p $APP_TEMP_PATH && touch $APP_SETUP_LOCK; }
function unlock_setup { rm -rf $APP_SETUP_LOCK; }
function wait_setup { echo "Waiting for app setup to finish..."; sleep $APP_SETUP_WAIT; }

# 2: 'Unlock' the setup process if the script exits prematurely:
trap unlock_setup HUP INT QUIT KILL TERM EXIT

# 3: Wait for postgres to come up
echo "DB is not ready, sleeping..."
until nc -vz postgres 5432 &>/dev/null; do
  sleep 1
done
echo "DB is ready, starting Rails."

# 4: Specify a default command, in case it wasn't issued:
if [ -z "$1" ]; then set -- bundle exec rails server -p 3000 -b 0.0.0.0 "$@"; fi

# 5: Run the checks only if the app code is executed:
if [[ "$3" = "rails" ]]
then
  # Clean up any orphaned lock file
  unlock_setup
  # 6: Wait until the setup 'lock' file no longer exists:
  while [ -f $APP_SETUP_LOCK ]; do wait_setup; done
  # 7: 'Lock' the setup process, to prevent a race condition when the
  # project's app containers will try to install gems and set up the
  # database concurrently:
  lock_setup
  # 8: Check if dependencies need to be installed and install them
  bundle install
  yarn install
  # 9: Run migrations or set up the database if it doesn't exist
  # Rails >= 6
  bundle exec rails db:prepare
  # Rails < 6
  # bundle exec rake db:migrate 2>/dev/null || bundle exec rake db:setup
  # 10: 'Unlock' the setup process:
  unlock_setup
  # 11: If the command to execute is 'rails server', then we must remove any
  # pid file present. Suddenly killing and removing app containers might leave
  # this file, and prevent rails from starting-up if present:
  if [[ "$4" = "s" || "$4" = "server" ]]; then rm -rf /app/tmp/pids/server.pid; fi
fi
# 12: Replace the shell with the given command:
exec "$@"

Great Gist, even two years on ;-) I also love the blog on hint.io. But allow me one question: In entrypoint.sh, you call unlock_setup followed by while [ -f $APP_SETUP_LOCK ]; do wait_setup; done -- but if I am not mistaken, the call to unlock_setup will basically render the locking mechanism ineffective? It seems to me that this function call is erroneous, or am I missing something?

@bovender Thanks for the kind words! I have gone back and forth on that section of the entrypoint with my team over the years. I honestly believe we landed there because if a setup.lock file did not get cleaned up for some reason when the entrypoint was run again it would stall the starting of the app. Feel free to experiment with it to see what works best in your situation.

Thanks!