a minimum rails environment with docker-compose

docker-compose.yml

version: '3'
services:
  mysql:
    image: mysql:5.7.19
    environment:
      MYSQL_ALLOW_EMPTY_PASSWORD: 'yes'
  rails:
    build: .
    environment:
      DATABASE_HOST: mysql
    volumes:
      - .:/opt/app
    ports:
      - 3000:3000
    links:
      - mysql

Dockerfile

FROM ruby:2.4.1-alpine

ENV RAILS_ROOT /opt/app
RUN mkdir -p $RAILS_ROOT
WORKDIR $RAILS_ROOT

RUN set -x \
  && apk upgrade --no-cache \
  && apk add --no-cache --virtual build-dependencies \
    less \
    tzdata \
    build-base \
    mysql-dev \
    nodejs \
  && apk add --no-cache \
    libxml2-dev \
    libxslt-dev \
  && gem install --no-document nokogiri \
    -- --use-system-libraries \
    --with-xml2-config=/usr/bin/xml2-config \
    --with-xslt-config=/usr/bin/xslt-config \
  && gem install --no-document bundler rails

COPY . $RAILS_ROOT
RUN bundle install
CMD ["./bin/rails", "server", "-b", "0.0.0.0"]