Compose file version 1 reference

Estimated reading time: 14 minutes

Reference and guidelines

These topics describe version 1 of the Compose file format. This is the oldest 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.

This table shows which Compose file versions support specific Docker releases.

Compose file format	Docker Engine release
3.7	18.06.0+
3.6	18.02.0+
3.5	17.12.0+
3.4	17.09.0+
3.3	17.06.0+
3.2	17.04.0+
3.1	1.13.1+
3.0	1.13.0+
2.4	17.12.0+
2.3	17.06.0+
2.2	1.13.0+
2.1	1.12.0+
2.0	1.10.0+
1.0	1.9.1.+

In addition to Compose file format versions shown in the table, the Compose itself is on a release schedule, as shown in Compose releases, but file format versions do not necessarily increment with each release. For example, Compose file format 3.0 was first introduced in Compose release 1.10.0, and versioned gradually in subsequent releases.

Service configuration reference

The Version 1 Compose file is a YAML file that defines services.

The default path for a Compose file is ./docker-compose.yml.

Tip: You can use either a .yml or .yaml extension for this file. They both work.

A service definition contains configuration which is applied to each container started for that service, much like passing command-line parameters to docker run.

As with docker run, options specified in the Dockerfile, such as CMD, EXPOSE, VOLUME, ENV, are respected by default - you don’t need to specify them again in docker-compose.yml.

This section contains a list of all configuration options supported by a service definition in version 1.

build

Configuration options that are applied at build time.

build can specified as a string containing a path to the build context.

build: ./dir

Note

In version 1 file format, build is different in two ways:

Only the string form (build: .) is allowed - not the object form that is allowed in Version 2 and up.

Using build together with image is not allowed. Attempting to do so results in an error.

dockerfile

Alternate Dockerfile.

Compose uses an alternate file to build with. A build path must also be specified.

  build: .
  dockerfile: Dockerfile-alternate

Note

In the version 1 file format, dockerfile is different from newer versions in two ways:

It appears alongside build, not as a sub-option:

Using dockerfile together with image is not allowed. Attempting to do so results in an error.

cap_add, cap_drop

Add or drop container capabilities. See man 7 capabilities for a full list.

cap_add:
  - ALL

cap_drop:
  - NET_ADMIN
  - SYS_ADMIN

Note: These options are ignored when deploying a stack in swarm mode with a (version 3) Compose file.

command

Override the default command.

command: bundle exec thin -p 3000

The command can also be a list, in a manner similar to dockerfile:

command: ["bundle", "exec", "thin", "-p", "3000"]

cgroup_parent

Specify an optional parent cgroup for the container.

cgroup_parent: m-executor-abcd

container_name

Specify a custom container name, rather than a generated default name.

container_name: my-web-container

Because Docker container names must be unique, you cannot scale a service beyond 1 container if you have specified a custom name. Attempting to do so results in an error.

devices

List of device mappings. Uses the same format as the --device docker client create option.

devices:
  - "/dev/ttyUSB0:/dev/ttyUSB0"

dns

Custom DNS servers. Can be a single value or a list.

dns: 8.8.8.8
dns:
  - 8.8.8.8
  - 9.9.9.9

dns_search

Custom DNS search domains. Can be a single value or a list.

dns_search: example.com
dns_search:
  - dc1.example.com
  - dc2.example.com

entrypoint

Override the default entrypoint.

entrypoint: /code/entrypoint.sh

The entrypoint can also be a list, in a manner similar to dockerfile:

entrypoint:
    - php
    - -d
    - zend_extension=/usr/local/lib/php/extensions/no-debug-non-zts-20100525/xdebug.so
    - -d
    - memory_limit=-1
    - vendor/bin/phpunit

Note: Setting entrypoint both overrides any default entrypoint set on the service’s image with the ENTRYPOINT Dockerfile instruction, and clears out any default command on the image - meaning that if there’s a CMD instruction in the Dockerfile, it is ignored.

env_file

Add environment variables from a file. Can be a single value or a list.

If you have specified a Compose file with docker-compose -f FILE, paths in env_file are relative to the directory that file is in.

Environment variables specified in environment override these values.

env_file: .env

env_file:
  - ./common.env
  - ./apps/web.env
  - /opt/secrets.env

Compose expects each line in an env file to be in VAR=VAL format. Lines beginning with # are processed as comments and are ignored. Blank lines are also ignored.

# Set Rails/Rack environment
RACK_ENV=development

Note: If your service specifies a build option, variables defined in environment files are not automatically visible during the build.

The value of VAL is used as is and not modified at all. For example if the value is surrounded by quotes (as is often the case of shell variables), the quotes are included in the value passed to Compose.

Keep in mind that the order of files in the list is significant in determining the value assigned to a variable that shows up more than once. The files in the list are processed from the top down. For the same variable specified in file a.env and assigned a different value in file b.env, if b.env is listed below (after), then the value from b.env stands. For example, given the following declaration in docker-compose.yml:

services:
  some-service:
    env_file:
      - a.env
      - b.env

And the following files:

# a.env
VAR=1

and

# b.env
VAR=hello

$VAR is hello.

environment

Add environment variables. You can use either an array or a dictionary. Any boolean values; true, false, yes no, need to be enclosed in quotes to ensure they are not converted to True or False by the YML parser.

Environment variables with only a key are resolved to their values on the machine Compose is running on, which can be helpful for secret or host-specific values.

environment:
  RACK_ENV: development
  SHOW: 'true'
  SESSION_SECRET:

environment:
  - RACK_ENV=development
  - SHOW=true
  - SESSION_SECRET

Note: If your service specifies a build option, variables defined in environment are not automatically visible during the build.

expose

Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.

expose:
 - "3000"
 - "8000"

extends

Extend another service, in the current file or another, optionally overriding configuration.

You can use extends on any service together with other configuration keys. The extends value must be a dictionary defined with a required service and an optional file key.

extends:
  file: common.yml
  service: webapp

The service the name of the service being extended, for example web or database. The file is the location of a Compose configuration file defining that service.

If you omit the file Compose looks for the service configuration in the current file. The file value can be an absolute or relative path. If you specify a relative path, Compose treats it as relative to the location of the current file.

You can extend a service that itself extends another. You can extend indefinitely. Compose does not support circular references and docker-compose returns an error if it encounters one.

For more on extends, see the the extends documentation.

external_links

Link to containers started outside this docker-compose.yml or even outside of Compose, especially for containers that provide shared or common services. external_links follow semantics similar to links when specifying both the container name and the link alias (CONTAINER:ALIAS).

external_links:
 - redis_1
 - project_db_1:mysql
 - project_db_1:postgresql

extra_hosts

Add hostname mappings. Use the same values as the docker client --add-host parameter.

extra_hosts:
 - "somehost:162.242.195.82"
 - "otherhost:50.31.209.229"

An entry with the ip address and hostname is created in /etc/hosts inside containers for this service, e.g:

162.242.195.82  somehost
50.31.209.229   otherhost

image

Specify the image to start the container from. Can either be a repository/tag or a partial image ID.

image: redis
image: ubuntu:14.04
image: tutum/influxdb
image: example-registry.com:4000/postgresql
image: a4bc65fd

If the image does not exist, Compose attempts to pull it, unless you have also specified build, in which case it builds it using the specified options and tags it with the specified tag.

Note: In the version 1 file format, using build together with image is not allowed. Attempting to do so results in an error.

labels

Add metadata to containers using Docker labels. You can use either an array or a dictionary.

It’s recommended that you use reverse-DNS notation to prevent your labels from conflicting with those used by other software.

labels:
  com.example.description: "Accounting webapp"
  com.example.department: "Finance"
  com.example.label-with-empty-value: ""

labels:
  - "com.example.description=Accounting webapp"
  - "com.example.department=Finance"
  - "com.example.label-with-empty-value"

links

Link to containers in another service. Either specify both the service name and a link alias (SERVICE:ALIAS), or just the service name.

Links are a legacy option. We recommend using networks instead.

web:
  links:
   - db
   - db:database
   - redis

Containers for the linked service are reachable at a hostname identical to the alias, or the service name if no alias was specified.

Links also express dependency between services in the same way as depends_on, so they determine the order of service startup.

Note: If you define both links and networks, services with links between them must share at least one network in common in order to communicate.

log_driver

Version 1 file format only. In version 2 and up, use logging.

Specify a log driver. The default is json-file.

log_driver: syslog

log_opt

Version 1 file format only. In version 2 and up, use logging.

Specify logging options as key-value pairs. An example of syslog options:

log_opt:
  syslog-address: "tcp://192.168.0.42:123"

net

Version 1 file format only. In version 2 and up, use network_mode and networks.

Network mode. Use the same values as the docker client --net parameter. The container:... form can take a service name instead of a container name or id.

net: "bridge"
net: "host"
net: "none"
net: "container:[service name or container name/id]"

pid

pid: "host"

Sets the PID mode to the host PID mode. This turns on sharing between container and the host operating system the PID address space. Containers launched with this flag can access and manipulate other containers in the bare-metal machine’s namespace and vice versa.

ports

Expose ports. Either specify both ports (HOST:CONTAINER), or just the container port (an ephemeral host port is chosen).

Note: When mapping ports in the HOST:CONTAINER format, you may experience erroneous results when using a container port lower than 60, because YAML parses numbers in the format xx:yy as a base-60 value. For this reason, we recommend always explicitly specifying your port mappings as strings.

ports:
 - "3000"
 - "3000-3005"
 - "8000:8000"
 - "9090-9091:8080-8081"
 - "49100:22"
 - "127.0.0.1:8001:8001"
 - "127.0.0.1:5000-5010:5000-5010"
 - "6060:6060/udp"

security_opt

Override the default labeling scheme for each container.

security_opt:
  - label:user:USER
  - label:role:ROLE

stop_signal

Sets an alternative signal to stop the container. By default stop uses SIGTERM. Setting an alternative signal using stop_signal causes stop to send that signal instead.

stop_signal: SIGUSR1

ulimits

Override the default ulimits for a container. You can either specify a single limit as an integer or soft/hard limits as a mapping.

ulimits:
  nproc: 65535
  nofile:
    soft: 20000
    hard: 40000

volumes, volume_driver

Mount paths or named volumes, optionally specifying a path on the host machine (HOST:CONTAINER), or an access mode (HOST:CONTAINER:ro). For version 2 files, named volumes need to be specified with the top-level volumes key. When using version 1, the Docker Engine creates the named volume automatically if it doesn’t exist.

You can mount a relative path on the host, which expands relative to the directory of the Compose configuration file being used. Relative paths should always begin with . or ...

volumes:
  # Just specify a path and let the Engine create a volume
  - /var/lib/mysql

  # Specify an absolute path mapping
  - /opt/data:/var/lib/mysql

  # Path on the host, relative to the Compose file
  - ./cache:/tmp/cache

  # User-relative path
  - ~/configs:/etc/configs/:ro

  # Named volume
  - datavolume:/var/lib/mysql

If you do not use a host path, you may specify a volume_driver.

volume_driver: mydriver

There are several things to note, depending on which Compose file version you’re using:

For version 1 files, both named volumes and container volumes use the specified driver.
No path expansion is done if you have also specified a volume_driver. For example, if you specify a mapping of ./foo:/data, the ./foo part is passed straight to the volume driver without being expanded.

See Docker Volumes and Volume Plugins for more information.

volumes_from

Mount all of the volumes from another service or container, optionally specifying read-only access (ro) or read-write (rw). If no access level is specified, then read-write is used.

volumes_from:
 - service_name
 - service_name:ro

cpu_shares, cpu_quota, cpuset, domainname, hostname, ipc, mac_address, mem_limit, memswap_limit, mem_swappiness, privileged, read_only, restart, shm_size, stdin_open, tty, user, working_dir

Each of these is a single value, analogous to its docker run counterpart.

cpu_shares: 73
cpu_quota: 50000
cpuset: 0,1

user: postgresql
working_dir: /code

domainname: foo.com
hostname: foo
ipc: host
mac_address: 02:42:ac:11:65:43

mem_limit: 1000000000
memswap_limit: 2000000000
privileged: true

restart: always

read_only: true
shm_size: 64M
stdin_open: true
tty: true

Compose documentation

Rate this page: