---
description: Compose file reference
keywords: fig, composition, compose version 1, docker
redirect_from:
- /compose/yml
title: Compose file version 1 reference
toc_max: 4
toc_min: 1
---

## 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](compose-versioning.md)**.

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

## Service configuration reference

The Version 1 Compose file is a [YAML](http://yaml.org/) file that defines [services](#service-configuration-reference).

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 will be 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 (e.g., `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](compose-versioning.md#version-1),
`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`](#image) is not allowed.
Attempting to do so results in an error.

#### dockerfile

Alternate Dockerfile.

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

      build: .
      dockerfile: Dockerfile-alternate

> **Note**
>
> In the [version 1 file format](compose-versioning.md#version-1), `dockerfile` is different from newer versions in two ways:
>
>* It appears alongside `build`, not as a sub-option:
>
>*  Using `dockerfile` together with [`image`](#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](/engine/reference/commandline/stack_deploy.md)
> 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](/engine/reference/builder.md#cmd):

    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](/engine/reference/builder.md#entrypoint):

    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` will both override any default entrypoint set
> on the service's image with the `ENTRYPOINT` Dockerfile instruction, *and*
> clear out any default command on the image - meaning that if there's a `CMD`
> instruction in the Dockerfile, it will be 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](#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 `#` (i.e. comments) are ignored, as are blank lines.

    # Set Rails/Rack environment
    RACK_ENV=development

> **Note**: If your service specifies a [build](#build) option, variables
> defined in environment files will _not_ be 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 will be 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`:

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

And the following files:

```none
# a.env
VAR=1
```

and

```none
# b.env
VAR=hello
```

$VAR will be `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](#build) option, variables
> defined in `environment` will _not_ be 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](/compose/extends.md#extending-services).

### 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 will be 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](#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](compose-versioning.md#version-1), using [`build`](#build) together
> with `image` is not allowed. Attempting to do so results in an error.

### labels

Add metadata to containers using [Docker labels](/engine/userguide/labels-custom-metadata.md). 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.

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

Containers for the linked service will be 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](#depends_on), so they determine the order of service startup.

> **Note**: If you define both links and [networks](#networks), services with
> links between them must share at least one network in common in order to
> communicate.

### log_driver

> [Version 1 file format](compose-versioning#version-1) only. In version 2 and up, use
> [logging](/compose/compose-file/index.md#logging).

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

    log_driver: syslog

### log_opt

> [Version 1 file format](compose-versioning#version-1) only. In version 2 and up, use
> [logging](/compose/compose-file/index.md#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](compose-versioning.md#version-1) only. In version 2 and up, use
> [network_mode](/compose/compose-file/index.md#networkmode) and [networks](/compose/compose-file/index.md#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 will be able to access and manipulate other
containers in the bare-metal machine's namespace and vise-versa.

### ports

Expose ports. Either specify both ports (`HOST:CONTAINER`), or just the container
port (a random host port will be 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 will
> parse numbers in the format `xx:yy` as sexagesimal (base 60). 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` will cause
`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](compose-versioning#version-2), named volumes need to be specified with the
[top-level `volumes` key](compose-file-v2.md#volume-configuration-reference).
When using [version 1](compose-versioning#version-1), the Docker Engine will create the named
volume automatically if it doesn't exist.

You can mount a relative path on the host, which will expand 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](compose-versioning#versioning) you're using:

-   For [version 1 files](compose-versioning#version-1), both named volumes and
    container volumes will use the specified driver.

-   No path expansion will be done if you have also specified a `volume_driver`.
    For example, if you specify a mapping of `./foo:/data`, the `./foo` part
    will be passed straight to the volume driver without being expanded.

See [Docker Volumes](/engine/userguide/dockervolumes.md) and
[Volume Plugins](/engine/extend/plugins_volume.md) 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 will be 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](/engine/reference/run.md) 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

- [User guide](/compose/index.md)
- [Installing Compose](/compose/install/)
- [Compose file versions and upgrading](compose-versioning.md)
- [Get started with Django](/compose/django/)
- [Get started with Rails](/compose/rails/)
- [Get started with WordPress](/compose/wordpress/)
- [Command line reference](/compose/reference/)
