DC-Bundler

1-Dockerfile

FROM ruby:2.3-slim

RUN apt-get update && apt-get install -qq -y --no-install-recommends build-essential
# Ensure that our apt package list is updated and has basic build packages.

RUN mkdir -p /app
WORKDIR /app
COPY . .
# Add app files into docker image

COPY ./docker-entrypoint.sh /
RUN chmod +x /docker-entrypoint.sh
ENTRYPOINT ["/docker-entrypoint.sh"]
# Add bundle entry point to handle bundle cache

ENV BUNDLE_PATH=/bundle \
    BUNDLE_BIN=/bundle/bin \
    GEM_HOME=/bundle
ENV PATH="${BUNDLE_BIN}:${PATH}"
# Bundle installs with binstubs to our custom /bundle/bin volume path. 
# Let system use those stubs.

2-docker-entrypoint.sh

#!/bin/bash
# Interpreter identifier

set -e
# Exit on fail

bundle check || bundle install --binstubs="$BUNDLE_BIN"
# Ensure all gems installed. Add binstubs to bin which has been added to PATH in Dockerfile.

exec "$@"
# Finally call command issued to the docker service

3-docker-compose.yml

version: '3.1'
services:
  web:
    build: .
    command: "echo 'Insert a Gemfile dependent startup command here, like \"rails server\".'"
    ports:
      - '3000:3000'
    volumes:
      - bundle_cache:/bundle
      # Map bundle cache to named volume
      - .:/app
      # Map /app files back to host drive, and visa versa
volumes:
  bundle_cache:
  # Mount volume with default driver