As we've discussed, microservices solve a particular set of problems but introduce some new challenges of their own. One challenge that engineers on your team will probably run into is doing local development. With a monolith, there are fewer moving parts that have to be managed—usually, you can get away with just running a database and an application server on your workstation to get work done. As you start to create new microservices, however, the situation gets more complicated. 

Containers are a great way to manage this complexity. Docker is a popular, open source software containerization platform. Docker allows you to specify how to run your application as a container—a lightweight standardized unit for deployment. There are plenty of books and online documentation about Docker, so we won't go into too much detail here, just know that a container encapsulates all of the information needed to run your application. As mentioned, a monolith application will often require an application server and a database server at a minimum—these will each run in their own container.

Docker Compose is a tool for running multicontainer applications. Compose allows you to define your applications containers in a YAML configuration file. Using the information in this file, you can then build and run your application. Compose will manage all of the various services defined in the configuration file in separate containers, allowing you to run a complex system on your workstation for local development.

brew install docker-compose

apt-get install docker-compose

  FROM ruby:2.3.3
  RUN apt-get update -qq && apt-get install -y build-essential 
  libpq-dev nodejs
  RUN mkdir /pichat
  WORKDIR /pichat
  ADD Gemfile /pichat/Gemfile
  ADD Gemfile.lock /pichat/Gemfile.lock
  RUN bundle install
  ADD . /pichat

version: '3'
services:
  db:
    image: mysql:5.6.34
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root

  app:
    build: .
    environment:
      RAILS_ENV: development
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/pichat
    ports:
      - "3000:3000"
    depends_on:
      - db