docker-compose/docs/gettingstarted.md

Getting Started

Let's get started with a walkthrough of getting a simple Python web app running on Compose. It assumes a little knowledge of Python, but the concepts demonstrated here should be understandable even if you're not familiar with Python.

Installation and set-up

First, install Docker and Compose.

Next, you'll want to make a directory for the project:

$ mkdir composetest
$ cd composetest

Inside this directory, create app.py, a simple Python web app that uses the Flask framework and increments a value in Redis. Don't worry if you don't have Redis installed, docker is going to take care of that for you when we define services:

from flask import Flask
from redis import Redis

app = Flask(__name__)
redis = Redis(host='redis', port=6379)

@app.route('/')
def hello():
    redis.incr('hits')
    return 'Hello World! I have been seen %s times.' % redis.get('hits')

if __name__ == "__main__":
    app.run(host="0.0.0.0", debug=True)

Next, define the Python dependencies in a file called requirements.txt:

flask
redis

Create a Docker image

Now, create a Docker image containing all of your app's dependencies. You specify how to build the image using a file called Dockerfile:

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

This tells Docker to:

• Build an image starting with the Python 2.7 image.
• Add the current directory . into the path /code in the image.
• Set the working directory to /code.
• Install the Python dependencies.
• Set the default command for the container to python app.py

For more information on how to write Dockerfiles, see the Docker user guide and the Dockerfile reference.

You can build the image by running docker build -t web ..

Define services

Next, define a set of services using docker-compose.yml:

web:
  build: .
  ports:
   - "5000:5000"
  volumes:
   - .:/code
  links:
   - redis
redis:
  image: redis

This template defines two services, web and redis. The web service:

• Builds from the Dockerfile in the current directory.
• Forwards the exposed port 5000 on the container to port 5000 on the host machine.
• Mounts the current directory on the host to /code inside the container allowing you to modify the code without having to rebuild the image.
• Links the web container to the Redis service.

The redis service uses the latest public Redis image pulled from the Docker Hub registry.

Build and run your app with Compose

Now, when you run docker-compose up, Compose will pull a Redis image, build an image for your code, and start everything up:

$ docker-compose up
Pulling image redis...
Building web...
Starting composetest_redis_1...
Starting composetest_web_1...
redis_1 | [8] 02 Jan 18:43:35.576 # Server started, Redis version 2.8.3
web_1   |  * Running on http://0.0.0.0:5000/
web_1   |  * Restarting with stat

If you're using Docker Machine, then docker-machine ip MACHINE_VM will tell you its address and you can open http://MACHINE_VM_IP:5000 in a browser.

If you're using Docker on Linux natively, then the web app should now be listening on port 5000 on your Docker daemon host. If http://0.0.0.0:5000 doesn't resolve, you can also try http://localhost:5000.

You should get a message in your browser saying:

Hello World! I have been seen 1 times.

Refreshing the page will increment the number.

If you want to run your services in the background, you can pass the -d flag (for "detached" mode) to docker-compose up and use docker-compose ps to see what is currently running:

$ docker-compose up -d
Starting composetest_redis_1...
Starting composetest_web_1...
$ docker-compose ps
    Name                 Command            State       Ports
-------------------------------------------------------------------
composetest_redis_1   /usr/local/bin/run         Up
composetest_web_1     /bin/sh -c python app.py   Up      5000->5000/tcp

The docker-compose run command allows you to run one-off commands for your services. For example, to see what environment variables are available to the web service:

$ docker-compose run web env

See docker-compose --help to see other available commands. You can also install command completion for the bash and zsh shell, which will also show you available commands.

If you started Compose with docker-compose up -d, you'll probably want to stop your services once you've finished with them:

$ docker-compose stop

At this point, you have seen the basics of how Compose works.

• Next, try the quick start guide for Django, Rails, or WordPress.
• See the reference guides for complete details on the commands, the configuration file and environment variables.

More Compose documentation

• User guide
• Installing Compose
• Get started with Django
• Get started with Rails
• Get started with WordPress
• Command line reference
• Compose file reference