compose/docs/index.md

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# Overview of Docker Compose

Compose is a tool for defining and running multi-container applications with
Docker. With Compose, you define a multi-container application in a single
file, then spin your application up in a single command which does everything
that needs to be done to get it running.

Compose is great for development environments, staging servers, and CI. We don't
recommend that you use it in production yet.

Using Compose is basically a three-step process.

1. Define your app's environment with a `Dockerfile` so it can be
reproduced anywhere.
2. Define the services that make up your app in `docker-compose.yml` so
they can be run together in an isolated environment:
3. Lastly, run `docker-compose up` and Compose will start and run your entire app.

A `docker-compose.yml` looks like this:

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

Compose has commands for managing the whole lifecycle of your application:

 * Start, stop and rebuild services
 * View the status of running services
 * Stream the log output of running services
 * Run a one-off command on a service

## Compose documentation

- [Installing Compose](install.md)
- [Get started with Django](django.md)
- [Get started with Rails](rails.md)
- [Get started with WordPress](wordpress.md)
- [Command line reference](./reference/index.md)
- [Compose file reference](yml.md)

## Quick start

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](install.md).

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](#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`](http://docs.docker.com/reference/builder/):

    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](https://docs.docker.com/userguide/dockerimages/#building-an-image-from-a-dockerfile) and the [Dockerfile reference](http://docs.docker.com/reference/builder/).

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](https://registry.hub.docker.com/_/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](https://docs.docker.com/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](completion.md) 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](django.md),
  [Rails](rails.md), or [WordPress](wordpress.md).
- See the reference guides for complete details on the [commands](./reference/index.md), the
  [configuration file](yml.md) and [environment variables](env.md).

## Release Notes

To see a detailed list of changes for past and current releases of Docker
Compose, please refer to the [CHANGELOG](https://github.com/docker/compose/blob/master/CHANGELOG.md).

## Getting help

Docker Compose is under active development. If you need help, would like to
contribute, or simply want to talk about the project with like-minded
individuals, we have a number of open channels for communication.

* To report bugs or file feature requests: please use the [issue tracker on Github](https://github.com/docker/compose/issues).

* To talk about the project with people in real time: please join the
  `#docker-compose` channel on freenode IRC.

* To contribute code or documentation changes: please submit a [pull request on Github](https://github.com/docker/compose/pulls).

For more information and resources, please visit the [Getting Help project page](https://docs.docker.com/project/get-help/).