docker-compose.yml

version: '3'
services:
  db:
    image: postgres:9.6.5
    volumes:
      - db-data:/var/lib/postgresql/data
    ports:
      - 5432:5432
  app:
    tty: true
    stdin_open: true
    build: .
    command: ash -c "rm -f tmp/pids/server.pid && (bundle check || bundle install) && bundle exec rails s -b 0"
    volumes:
      - .:/app:cached
      - gems:/gems
      - yarn:/usr/local/share/.cache/yarn      
    ports:
      - 3000:3000
    depends_on:
      - db
    environment:
      DATABASE_URL: postgres://postgres@db/app
volumes:
  db-data:
  gems:
  yarn:

Dockerfile

FROM ruby:2.6-alpine

ENV LANG=C.UTF-8 \
    TZ=Asia/Tokyo \
    ROOT_PATH=/app \
    BUNDLE_JOBS=4 \
    BUNDLE_PATH=/gems

VOLUME /gems

RUN mkdir $ROOT_PATH
WORKDIR $ROOT_PATH

RUN apk add --update --no-cache \
      build-base \
      curl-dev \
      linux-headers \
      libxml2-dev \
      libxslt-dev \
      yaml-dev \
      zlib-dev \
      git \
      openssh \
      less \
      tzdata \
      postgresql-dev \
      libidn-dev \
      yaml \
      nodejs \
      npm
RUN npm install -g yarn