Basis Docker setup for Rails app (Postgres)

docker-compose.yml

version: '3.4'

services:

  app:
    restart: always
    build:
      context: .
      dockerfile: ./Dockerfile
      args:
        - SECRET_KEY_BASE
        - DATABASE_URL
    depends_on:
      - postgres
    volumes:
      - attachments:/app/app/uploads:delegated
      - ./seed:/app/seed
    environment:
      RAILS_ENV: production
      DATABASE_URL: "postgres://postgres:postgres@postgres:5432/app"
      SECRET_KEY_BASE: xxxxxxxxxxxx
      RAILS_LOG_TO_STDOUT: 1
      RAILS_SERVE_STATIC_FILES: 1
    command: /bin/sh -c "rm -f ./tmp/pids/server.pid && rails server -b 0.0.0.0"
    logging:
      driver: "json-file"
      options:
        max-size: "100k"
        max-file: "20"

  postgres:
    image: postgres:12.1
    restart: always
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
    volumes:
      - db_data:/var/lib/postgresql/data
    restart: on-failure
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5
    logging:
      driver: none

volumes:
  db_data:
  attachments:

Dockerfile

FROM ruby:2.7.1-alpine

ENV BUNDLER_VERSION=2.0.2

RUN apk add --update --no-cache \
      binutils-gold \
      build-base \
      curl \
      file \
      g++ \
      gcc \
      git \
      less \
      libstdc++ \
      libffi-dev \
      libc-dev \
      linux-headers \
      postgresql-client \
      libxml2-dev \
      libxml2-dev \
      imagemagick \
      libxslt-dev \
      libgcrypt-dev \
      make \
      netcat-openbsd \
      nodejs \
      openssl \
      pkgconfig \
      postgresql-dev \
      tzdata \
      yarn

RUN gem install -N bundler -v 2.1.2

WORKDIR /app

COPY entrypoint.sh /app/entrypoint.sh

WORKDIR /app/app
COPY app/Gemfile app/Gemfile.lock ./

RUN bundle config build.nokogiri --use-system-libraries
RUN bundle check || bundle install

COPY app/package.json app/yarn.lock ./

RUN yarn install --check-files

COPY app/. ./

RUN bundle add activerecord-nulldb-adapter && rm config/credentials.yml.enc

# copy database.yml with credentials OR config via DB_URL
RUN cp config/database.yml.example config/database.yml

RUN DB_ADAPTER=nulldb bundle exec rake assets:precompile RAILS_ENV=production SECRET_KEY_BASE=foobar

ENTRYPOINT ["/app/entrypoint.sh"]
CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0"]