hands-on-compose.md

Introducing docker-compose (former fig)

• used for running multi-container applications
• single file is used to define all inner workings of the application

Lets build simple web app with Flask and Redis

• Check that docker-compose is installed

  # host
  docker-compose --version

• lets create the directory for our application

  # host
  mkdir composetest
  cd composetest
  mkdir code

• code simple web app in python using Flask in code/app.py

  # file code/app.py
  
  from flask import Flask
  from redis import Redis
  from urlparse import urlparse
  import sys, os
  
  # extract the connection to redis from environment variable
  up = urlparse(os.environ['REDIS_PORT'])
  print >> sys.stderr, 'connecting to redis at %s:%s' % (up.hostname, up.port)
  
  # connect to redis
  redis = Redis(host=up.hostname, port=up.port)
  
  # create flask instancw
  app = Flask(__name__)
  
  # callback to reply to root url
  @app.route('/')
  def hello():
      redis.incr('hits')
      return 'Hi, you are visitor nr %s.' % redis.get('hits')
  
  # main: run flask
  if __name__ == "__main__":
      app.run(host="0.0.0.0", debug=True)

• specify the python dependencies for the web app in code/requirements.txt

  flask
  redis
  

• the configuration of the web app container goes in Dockerfile

  # Dockerfile
  FROM python:2.7
  ADD ./code /code
  RUN pip install -r /code/requirements.txt
  CMD python /code/app.py

• define compose configuration that combining elements together

  # docker-compose.yml
  web:
    build: .
    ports:
     - "5000"
    volumes:
     - ./code:/code
    links:
     - redis
    command: python /code/app.py
  
  redis:
    image: redis

• now run it all

  # host, in composetest
  docker-compose up

• in another terminal, get some information about your servers

  # host, in composetest
  docker-compose ps

• find the external port for the web app

  # host, in composetest
  docker-compose port web 5000

• direct your browser to the IP address of your host and use the proper port

• or in your terminal

 # host
 curl localhost:[port]