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Compose file reference
fig, composition, compose, versions, upgrading, docker
Compose file versions and upgrading

The Compose file is a YAML file defining services, networks, and volumes for a Docker application.

The Compose file formats are now described in these references, specific to each version.

Reference file What changed in this version
Version 3 (most current, and recommended) Version 3 updates
Version 2 Version 2 updates
Version 1 Version 1 updates

The topics below explain the differences among the versions, Docker Engine compatibility, and how to upgrade.

Compatibility matrix

There are several versions of the Compose file format – 1, 2, 2.x, and 3.x

{% include content/compose-matrix.md %}

Looking for more detail on Docker and Compose compatibility?

We recommend keeping up-to-date with newer releases as much as possible. However, if you are using an older version of Docker and want to determine which Compose release is compatible, refer to the Compose release notes. Each set of release notes gives details on which versions of Docker Engine are supported, along with compatible Compose file format versions. (See also, the discussion in issue #3404.)

For details on versions and how to upgrade, see Versioning and Upgrading.

Versioning

There are currently three versions of the Compose file format:

  • Version 1, the legacy format. This is specified by omitting a version key at the root of the YAML.

  • Version 2.x. This is specified with a version: '2' or version: '2.1', etc., entry at the root of the YAML.

  • Version 3.x, the latest and recommended version, designed to be cross-compatible between Compose and the Docker Engine's swarm mode. This is specified with a version: '3' or version: '3.1', etc., entry at the root of the YAML.

v2 and v3 Declaration

Note: When specifying the Compose file version to use, make sure to specify both the major and minor numbers. If no minor version is given, 0 is used by default and not the latest minor version.

The Compatibility Matrix shows Compose file versions mapped to Docker Engine releases.

To move your project to a later version, see the Upgrading section.

Note: If you're using multiple Compose files or extending services, each file must be of the same version - you cannot, for example, mix version 1 and 2 in a single project.

Several things differ depending on which version you use:

  • The structure and permitted configuration keys
  • The minimum Docker Engine version you must be running
  • Compose's behaviour with regards to networking

These differences are explained below.

Version 1

Compose files that do not declare a version are considered "version 1". In those files, all the services are declared at the root of the document.

Version 1 is supported by Compose up to 1.6.x. It will be deprecated in a future Compose release.

Version 1 files cannot declare named volumes, networks or build arguments.

Compose does not take advantage of networking when you use version 1: every container is placed on the default bridge network and is reachable from every other container at its IP address. You need to use links to enable discovery between containers.

Example:

web:
  build: .
  ports:
   - "5000:5000"
  volumes:
   - .:/code
  links:
   - redis
redis:
  image: redis

Version 2

Compose files using the version 2 syntax must indicate the version number at the root of the document. All services must be declared under the services key.

Version 2 files are supported by Compose 1.6.0+ and require a Docker Engine of version 1.10.0+.

Named volumes can be declared under the volumes key, and networks can be declared under the networks key.

By default, every container joins an application-wide default network, and is discoverable at a hostname that's the same as the service name. This means links are largely unnecessary. For more details, see Networking in Compose.

Note: When specifying the Compose file version to use, make sure to specify both the major and minor numbers. If no minor version is given, 0 is used by default and not the latest minor version. As a result, features added in later versions will not be supported. For example:

version: "2"

is equivalent to:

version: "2.0"

Simple example:

version: "{{ site.compose_file_v2 }}"
services:
  web:
    build: .
    ports:
     - "5000:5000"
    volumes:
     - .:/code
  redis:
    image: redis

A more extended example, defining volumes and networks:

version: "{{ site.compose_file_v2 }}"
services:
  web:
    build: .
    ports:
     - "5000:5000"
    volumes:
     - .:/code
    networks:
      - front-tier
      - back-tier
  redis:
    image: redis
    volumes:
      - redis-data:/var/lib/redis
    networks:
      - back-tier
volumes:
  redis-data:
    driver: local
networks:
  front-tier:
    driver: bridge
  back-tier:
    driver: bridge

Several other options were added to support networking, such as:

  • aliases

  • The depends_on option can be used in place of links to indicate dependencies between services and startup order.

    version: "{{ site.compose_file_v2 }}"
services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
  db:
    image: postgres

  • ipv4_address, ipv6_address

Variable substitution also was added in Version 2.

Version 2.1

An upgrade of version 2 that introduces new parameters only available with Docker Engine version 1.12.0+. Version 2.1 files are supported by Compose 1.9.0+.

Introduces the following additional parameters:

Version 2.2

An upgrade of version 2.1 that introduces new parameters only available with Docker Engine version 1.13.0+. Version 2.2 files are supported by Compose 1.13.0+. This version also allows you to specify default scale numbers inside the service's configuration.

Introduces the following additional parameters:

Version 2.3

An upgrade of version 2.2 that introduces new parameters only available with Docker Engine version 17.06.0+. Version 2.3 files are supported by Compose 1.16.0+.

Introduces the following additional parameters:

Version 2.4

An upgrade of version 2.3 that introduces new parameters only available with Docker Engine version 17.12.0+. Version 2.4 files are supported by Compose 1.21.0+.

Introduces the following additional parameters:

  • platform for service definitions
  • Support for extension fields at the root of service, network, and volume definitions

Version 3

Designed to be cross-compatible between Compose and the Docker Engine's swarm mode, version 3 removes several options and adds several more.

  • Removed: volume_driver, volumes_from, cpu_shares, cpu_quota, cpuset, mem_limit, memswap_limit, extends, group_add. See the upgrading guide for how to migrate away from these. (For more information on extends, see Extending services.)

  • Added: deploy

Note: When specifying the Compose file version to use, make sure to specify both the major and minor numbers. If no minor version is given, 0 is used by default and not the latest minor version. As a result, features added in later versions will not be supported. For example:

version: "3"

is equivalent to:

version: "3.0"

Version 3.3

An upgrade of version 3 that introduces new parameters only available with Docker Engine version 17.06.0+, and higher.

Introduces the following additional parameters:

Version 3.4

An upgrade of version 3 that introduces new parameters. It is only available with Docker Engine version 17.09.0 and higher.

Introduces the following additional parameters:

Version 3.5

An upgrade of version 3 that introduces new parameters. It is only available with Docker Engine version 17.12.0 and higher.

Introduces the following additional parameters:

Version 3.6

An upgrade of version 3 that introduces new parameters. It is only available with Docker Engine version 18.02.0 and higher.

Introduces the following additional parameters:

Version 3.7

An upgrade of version 3 that introduces new parameters. It is only available with Docker Engine version 18.06.0 and higher.

Introduces the following additional parameters:

  • init in service definitions
  • rollback_config in deploy configurations
  • Support for extension fields at the root of service, network, volume, secret and config definitions

Upgrading

Version 2.x to 3.x

Between versions 2.x and 3.x, the structure of the Compose file is the same, but several options have been removed:

  • volume_driver: Instead of setting the volume driver on the service, define a volume using the top-level volumes option and specify the driver there.

    version: "{{ site.compose_file_v3 }}"
services:
  db:
    image: postgres
    volumes:
      - data:/var/lib/postgresql/data
volumes:
  data:
    driver: mydriver

  • volumes_from: To share a volume between services, define it using the top-level volumes option and reference it from each service that shares it using the service-level volumes option.

  • cpu_shares, cpu_quota, cpuset, mem_limit, memswap_limit: These have been replaced by the resources key under deploy. deploy configuration only takes effect when using docker stack deploy, and is ignored by docker-compose.

  • extends: This option has been removed for version: "3.x" Compose files. (For more information, see Extending services.)

  • group_add: This option has been removed for version: "3.x" Compose files.

  • pids_limit: This option has not been introduced in version: "3.x" Compose files.

  • link_local_ips in networks: This option has not been introduced in version: "3.x" Compose files.

Version 1 to 2.x

In the majority of cases, moving from version 1 to 2 is a very simple process:

  1. Indent the whole file by one level and put a services: key at the top.
  2. Add a version: '2' line at the top of the file.

It's more complicated if you're using particular configuration features:

  • dockerfile: This now lives under the build key:

    build:
  context: .
  dockerfile: Dockerfile-alternate

  • log_driver, log_opt: These now live under the logging key:

    logging:
  driver: syslog
  options:
    syslog-address: "tcp://192.168.0.42:123"

  • links with environment variables: As documented in the environment variables reference, environment variables created by links have been deprecated for some time. In the new Docker network system, they have been removed. You should either connect directly to the appropriate hostname or set the relevant environment variable yourself, using the link hostname:

    web:
  links:
    - db
  environment:
    - DB_PORT=tcp://db:5432

  • external_links: Compose uses Docker networks when running version 2 projects, so links behave slightly differently. In particular, two containers must be connected to at least one network in common in order to communicate, even if explicitly linked together.

    Either connect the external container to your app's default network, or connect both the external container and your service's containers to an external network.

  • net: This is now replaced by network_mode:

    net: host    ->  network_mode: host
net: bridge  ->  network_mode: bridge
net: none    ->  network_mode: none

    If you're using net: "container:[service name]", you must now use network_mode: "service:[service name]" instead.

    net: "container:web"  ->  network_mode: "service:web"

    If you're using net: "container:[container name/id]", the value does not need to change.

    net: "container:cont-name"  ->  network_mode: "container:cont-name"
net: "container:abc12345"   ->  network_mode: "container:abc12345"

  • volumes with named volumes: these must now be explicitly declared in a top-level volumes section of your Compose file. If a service mounts a named volume called data, you must declare a data volume in your top-level volumes section. The whole file might look like this:

    version: "{{ site.compose_file_v2 }}"
services:
  db:
    image: postgres
    volumes:
      - data:/var/lib/postgresql/data
volumes:
  data: {}

    By default, Compose creates a volume whose name is prefixed with your project name. If you want it to just be called data, declare it as external:

    volumes:
  data:
    external: true

Compatibility mode

docker-compose 1.20.0 introduces a new --compatibility flag designed to help developers transition to version 3 more easily. When enabled, docker-compose reads the deploy section of each service's definition and attempts to translate it into the equivalent version 2 parameter. Currently, the following deploy keys are translated:

All other keys are ignored and produce a warning if present. You can review the configuration that will be used to deploy by using the --compatibility flag with the config command.

Do not use this in production!

We recommend against using --compatibility mode in production. Because the resulting configuration is only an approximate using non-Swarm mode properties, it may produce unexpected results.

Compose file format references