Notepad/enter/Coding Tips (Classical)/Terminal Tips/System Client/Servers/Virtual Machines/Docker/Docker Compose.md

via the Docker docs

Key features and use cases of Docker Compose

Using Compose is essentially 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 a compose.yaml file so they can be run together in an isolated environment.

3. Run docker compose up and the Docker compose command starts and runs your entire app.

A compose.yaml looks like this:

services:
  web:
    build: .
    ports:
      - "8000:5000"
    volumes:
      - .:/code
      - logvolume01:/var/log
    depends_on:
      - redis
  redis:
    image: redis
volumes:
  logvolume01: {}

For more information about the Compose file, see the Compose file reference.

Key features of Docker Compose

Have 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, such as when 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 base name 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.

The default project directory is the base directory of the Compose file. A custom value for it can be defined with the --project-directory command line option.

Preserves 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 Environment variables and adjust the necessary environment variables for your 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.

Supports 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.

You can extend a Compose file using the extends field or by creating multiple Compose files. For more details, see Working with multiple Compose files.

Common use cases of Docker Compose

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.