What is the difference between docker and docker-compose

The docker cli is used when managing individual containers on a docker engine. It is the client command line to access the docker daemon api.

The docker-compose cli can be used to manage a multi-container application. It also moves many of the options you would enter on the docker run cli into the docker-compose.yml file for easier reuse. It works as a front end "script" on top of the same docker api used by docker, so you can do everything docker-compose does with docker commands and a lot of shell scripting. See this documentation on docker-compose for more details.

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Update for Swarm Mode

Since this answer was posted, docker has added a second use of docker-compose.yml files. Starting with the version 3 yml format and docker 1.13, you can use the yml with docker-compose and also to define a stack in docker's swarm mode. To do the latter you need to use docker stack deploy -c docker-compose.yml $stack_name instead of docker-compose up and then manage the stack with docker commands instead of docker-compose commands. The mapping is a one for one between the two uses:

• Compose Project -> Swarm Stack: A group of services for a specific purpose
• Compose Service -> Swarm Service: One image and it's configuration, possibly scaled up.
• Compose Container -> Swarm Task: A single container in a service

For more details on swarm mode, see docker's swarm mode documentation.

docker manages single containers

docker-compose manages multiple container applications

Usage of docker-compose requires 3 steps:

1. Define the app environment with a Dockerfile
2. Define the app services in docker-compose.yml
3. Run docker-compose up to start and run app

Below is a docker-compose.yml example taken from the docker docs:

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