Overview of Docker Compose

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 servicesfrom your configuration. To learn more about all the features of Composesee the list of features.

Compose is great for development, testing, and staging environments, as well asCI workflows. You can learn more about each case inCommon Use Cases.

Using Compose is basically a three-step process.

1. Define your app’s environment with a Dockerfile so it can bereproduced anywhere.
2. Define the services that make up your app in docker-compose.yml sothey 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

For more information about the Compose file, see theCompose 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

• Installing Compose
• Getting Started
• Get started with Django
• Get started with Rails
• Get started with WordPress
• Frequently asked questions
• Command line reference
• Compose file reference

Features

The features of Compose that make it effective are:

• Multiple isolated environments on a single host
• Preserve volume data when containers are created
• Only recreate containers that have changed
• 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 usethis project name to:

• on a dev host, to create multiple copies of a single environment (ex: you wantto 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 setthe project name to a unique build number
• on a shared host or dev host, to prevent different projects which may use thesame service names, from interfering with each other

The default project name is the basename of the project directory. You can seta custom project name by using the-p command line option or theCOMPOSE_PROJECT_NAME environment variable.

Preserve volume data when containers are created

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

Only recreate containers that have changed

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

Variables and moving a composition between environments

Compose supports variables in the Compose file. You can use these variablesto customize your composition for different environments, or different users.See Variable substitution for moredetails.

You can extend a Compose file using the extends field or by creating multipleCompose files. See extends for more details.

Common Use Cases

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

Development environments

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

The Compose file provides a way to document and configureall of the application’s service dependencies (databases, queues, caches,web service APIs, etc). Using the Compose command line tool you can createand 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 getstarted on a project. Compose can reduce a multi-page “developer gettingstarted 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 processis the automated test suite. Automated end-to-end testing requires anenvironment in which to run tests. Compose provides a convenient way to createand destroy isolated testing environments for your test suite. By defining the fullenvironment in a Compose file you can create and destroy theseenvironments in just a few commands:

$ docker-compose up -d
$ ./run_tests
$ docker-compose stop
$ docker-compose rm -f

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 maybe a single instance provisioned withDocker Machine or an entireDocker Swarm cluster.

For details on using production-oriented features, seecompose in production in this documentation.

Release Notes

To see a detailed list of changes for past and current releases of DockerCompose, please refer to theCHANGELOG.

Getting help

Docker Compose is under active development. If you need help, would like tocontribute, or simply want to talk about the project with like-mindedindividuals, 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.