Overview of Docker Compose

Estimated reading time: 5 minutes

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.

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.

Using Compose is basically a three-step process.

Define your app’s environment with a Dockerfile so it can be reproduced anywhere.
Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.
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 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

Features

The features of Compose that make it effective are:

Multiple isolated environments on a single host

Compose uses a project name to isolate environments from each other. You can make use of this project name in several different contexts:

on a dev host, to create multiple copies of a single environment (e.g., 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 or the COMPOSE_PROJECT_NAME environment variable.

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.

If you use docker-compose on a Windows machine, see Environmentvariables and adjust the necessary environment variables for you specific needs.

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 for more details.

You can extend a Compose file using the extends field or by creating multiple Compose files. See extends 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 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 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 or an entire Docker Swarm cluster.

For details on using production-oriented features, see compose in production 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.

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.
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.

For more information and resources, please visit the Getting Help project page.

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