compose/docs/overview.md

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# Overview of Docker Compose

Compose is a tool for defining and running multi-container Docker applications.
With Compose, you use a Compose file to configure your application's services.
Then, using a single command, you create and start all the services
from your configuration. To learn more about all the features of Compose
see [the list of features](#features).

Compose is great for development, testing, and staging environments, as well as
CI workflows. You can learn more about each case in
[Common Use Cases](#common-use-cases).

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:

    version: '2'
    services:
      web:
        build: .
        ports:
         - "5000:5000"
        volumes:
         - .:/code
         - logvolume01:/var/log
        links:
         - redis
      redis:
        image: redis
    volumes:
      logvolume01: {}

For more information about the Compose file, see the
[Compose file reference](compose-file.md)

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)
- [Getting Started](gettingstarted.md)
- [Get started with Django](django.md)
- [Get started with Rails](rails.md)
- [Get started with WordPress](wordpress.md)
- [Frequently asked questions](faq.md)
- [Command line reference](./reference/index.md)
- [Compose file reference](compose-file.md)

## Features

The features of Compose that make it effective are:

* [Multiple isolated environments on a single host](#Multiple-isolated-environments-on-a-single-host)
* [Preserve volume data when containers are created](#preserve-volume-data-when-containers-are-created)
* [Only recreate containers that have changed](#only-recreate-containers-that-have-changed)
* [Variables and moving a composition between environments](#variables-and-moving-a-composition-between-environments)

### Multiple isolated environments on a single host

Compose uses a project name to isolate environments from each other. You can use
this project name to:

* on a dev host, to create multiple copies of a single environment (ex: you want
  to run a stable copy for each feature branch of a project)
* on a CI server, to keep builds from interfering with each other, you can set
  the project name to a unique build number
* on a shared host or dev host, to prevent different projects which may use the
  same service names, from interfering with each other

The default project name is the basename of the project directory. You can set
a custom project name by using the
[`-p` command line option](./reference/overview.md) or the
[`COMPOSE_PROJECT_NAME` environment variable](./reference/envvars.md#compose-project-name).

### Preserve volume data when containers are created

Compose preserves all volumes used by your services. When `docker-compose up`
runs, if it finds any containers from previous runs, it copies the volumes from
the old container to the new container. This process ensures that any data
you've created in volumes isn't lost.


### Only recreate containers that have changed

Compose caches the configuration used to create a container. When you
restart a service that has not changed, Compose re-uses the existing
containers. Re-using containers means that you can make changes to your
environment very quickly.


### Variables and moving a composition between environments

Compose supports variables in the Compose file. You can use these variables
to customize your composition for different environments, or different users.
See [Variable substitution](compose-file.md#variable-substitution) for more
details.

You can extend a Compose file using the `extends` field or by creating multiple
Compose files. See [extends](extends.md) for more details.


## Common Use Cases

Compose can be used in many different ways. Some common use cases are outlined
below.

### Development environments

When you're developing software, the ability to run an application in an
isolated environment and interact with it is crucial.  The Compose command
line tool can be used to create the environment and interact with it.

The [Compose file](compose-file.md) provides a way to document and configure
all of the application's service dependencies (databases, queues, caches,
web service APIs, etc). Using the Compose command line tool you can create
and start one or more containers for each dependency with a single command
(`docker-compose up`).

Together, these features provide a convenient way for developers to get
started on a project.  Compose can reduce a multi-page "developer getting
started guide" to a single machine readable Compose file and a few commands.

### Automated testing environments

An important part of any Continuous Deployment or Continuous Integration process
is the automated test suite. Automated end-to-end testing requires an
environment in which to run tests. Compose provides a convenient way to create
and destroy isolated testing environments for your test suite. By defining the full
environment in a [Compose file](compose-file.md) you can create and destroy these
environments in just a few commands:

    $ docker-compose up -d
    $ ./run_tests
    $ docker-compose down

### Single host deployments

Compose has traditionally been focused on development and testing workflows,
but with each release we're making progress on more production-oriented features.
You can use Compose to deploy to a remote Docker Engine. The Docker Engine may
be a single instance provisioned with
[Docker Machine](https://docs.docker.com/machine/) or an entire
[Docker Swarm](https://docs.docker.com/swarm/) cluster.

For details on using production-oriented features, see
[compose in production](production.md) in this documentation.


## 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/opensource/get-help/).