--- description: Compose file reference keywords: fig, composition, compose, docker redirect_from: - /compose/yml - /compose/compose-file-v3/ title: Compose file version 3 reference toc_max: 4 toc_min: 1 --- ## Reference and guidelines These topics describe version 3 of the Compose file format. This is the newest version. ## Compose and Docker compatibility matrix There are several versions of the Compose file format – 1, 2, 2.x, and 3.x. The table below is a quick look. For full details on what each version includes and how to upgrade, see **[About versions and upgrading](compose-versioning.md)**. {% include content/compose-matrix.md %} ## Compose file structure and examples Here is a sample Compose file from the voting app sample used in the [Docker for Beginners lab](https://github.com/docker/labs/tree/master/beginner/) topic on [Deploying an app to a Swarm](https://github.com/docker/labs/blob/master/beginner/chapters/votingapp.md): 

version: "{{ site.compose_file_v3 }}"
services:

  redis:
    image: redis:alpine
    ports:
      - "6379"
    networks:
      - frontend
    deploy:
      replicas: 2
      update_config:
        parallelism: 2
        delay: 10s
      restart_policy:
        condition: on-failure

  db:
    image: postgres:9.4
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - backend
    deploy:
      placement:
        max_replicas_per_node: 1
        constraints:
          - "node.role==manager"

  vote:
    image: dockersamples/examplevotingapp_vote:before
    ports:
      - "5000:80"
    networks:
      - frontend
    depends_on:
      - redis
    deploy:
      replicas: 2
      update_config:
        parallelism: 2
      restart_policy:
        condition: on-failure

  result:
    image: dockersamples/examplevotingapp_result:before
    ports:
      - "5001:80"
    networks:
      - backend
    depends_on:
      - db
    deploy:
      replicas: 1
      update_config:
        parallelism: 2
        delay: 10s
      restart_policy:
        condition: on-failure

  worker:
    image: dockersamples/examplevotingapp_worker
    networks:
      - frontend
      - backend
    deploy:
      mode: replicated
      replicas: 1
      labels: [APP=VOTING]
      restart_policy:
        condition: on-failure
        delay: 10s
        max_attempts: 3
        window: 120s
      placement:
        constraints:
          - "node.role==manager"

  visualizer:
    image: dockersamples/visualizer:stable
    ports:
      - "8080:8080"
    stop_grace_period: 1m30s
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock"
    deploy:
      placement:
        constraints:
          - "node.role==manager"

networks:
  frontend:
  backend:

volumes:
  db-data:
The topics on this reference page are organized alphabetically by top-level key to reflect the structure of the Compose file itself. Top-level keys that define a section in the configuration file such as `build`, `deploy`, `depends_on`, `networks`, and so on, are listed with the options that support them as sub-topics. This maps to the `: