docker
/
docs
mirror of https://github.com/docker/docs.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

added drafts of versioned compose reference files 

pruning Compose file v2 reference

updated Compose v1, v2, v3 files, still WIP

added includes for compatibility matrix, fixed TOC menu

new topic organziation Compose reference, split two 3 files plus versioning

Daniel's comments, fixed links, added more to versioning details

fixed volumes_from example per Daniel's comments for v1

simplified links to version references

copyedits and improved/surfaced links to versioning/upgrade docs

removed for version specific content re: volume_drivers from various files

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
This commit is contained in:
Victoria Bialas 2017-02-02 15:25:17 -08:00
parent e322b5974c
commit 55b004036a
7 changed files with 2135 additions and 530 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
_data/toc.yaml
View File

@ -799,8 +799,16 @@ toc:
title: Networking in Compose
- path: /compose/production/
title: Using Compose in Production
- path: /compose/compose-file/
title: Compose File Reference
- sectiontitle: Compose File Reference
section:
- path: /compose/compose-file/
title: Version 3 reference
- path: /compose/compose-file/compose-file-v2/
title: Version 2 reference
- path: /compose/compose-file/compose-file-v1/
title: Version 1 reference
- path: /compose/compose-file/compose-versioning/
title: About versions and upgrading
- sectiontitle: Command-line Reference
section:
- path: /compose/reference/overview/

13
_includes/content/compose-matrix.md Normal file
View File

@ -0,0 +1,13 @@
There are several versions of the Compose file format – 1, 2, 2.1 and 3. For
details on versions and how to upgrade, see
[Versioning](compose-versioning.md#versioning) and
[Upgrading](compose-versioning.md#upgrading).
This table shows which Compose file versions support specific Docker releases.
| **Compose file format** | **Docker Engine release** |
| ------------------- | ------------------ |
| 3.0 ; 3.1 | 1.13.0+ |
| 2.1 | 1.12.0+ |
| 2.0 | 1.10.0+ |
| 1.0 | 1.9.1.+ |

54
_includes/content/compose-var-sub.md Normal file
View File

@ -0,0 +1,54 @@
Your configuration options can contain environment variables. Compose uses the
variable values from the shell environment in which `docker-compose` is run.
For example, suppose the shell contains `EXTERNAL_PORT=8000` and you supply
this configuration:
web:
build: .
ports:
- "${EXTERNAL_PORT}:5000"
When you run `docker-compose up` with this configuration, Compose looks for
the `EXTERNAL_PORT` environment variable in the shell and substitutes its
value in. In this example, Compose resolves the port mapping to `"8000:5000"`
before creating the `web` container.
If an environment variable is not set, Compose substitutes with an empty
string. In the example above, if `EXTERNAL_PORT` is not set, the value for the
port mapping is `:5000` (which is of course an invalid port mapping, and will
result in an error when attempting to create the container).
You can set default values for environment variables using a
[`.env` file](env-file.md), which Compose will automatically look for. Values
set in the shell environment will override those set in the `.env` file.
$ unset EXTERNAL_PORT
$ echo "EXTERNAL_PORT=6000" > .env
$ docker-compose up # EXTERNAL_PORT will be 6000
$ export EXTERNAL_PORT=7000
$ docker-compose up # EXTERNAL_PORT will be 7000
Both `$VARIABLE` and `${VARIABLE}` syntax are supported.
Additionally when using the [2.1 file format](compose-versioning.md#version-21), it
is possible to provide inline default values using typical shell syntax:
- `${VARIABLE:-default}` will evaluate to `default` if `VARIABLE` is unset or
empty in the environment.
- `${VARIABLE-default}` will evaluate to `default` only if `VARIABLE` is unset
in the environment.
Other extended shell-style features, such as `${VARIABLE/foo/bar}`, are not
supported.
You can use a `$$` (double-dollar sign) when your configuration needs a literal
dollar sign. This also prevents Compose from interpolating a value, so a `$$`
allows you to refer to environment variables that you don't want processed by
Compose.
web:
build: .
command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
If you forget and use a single dollar sign (`$`), Compose interprets the value as an environment variable and will warn you:
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.

512
compose/compose-file/compose-file-v1.md Normal file
View File

@ -0,0 +1,512 @@
---
description: Compose file reference
keywords: fig, composition, compose version 1, docker
redirect_from:
- /compose/yml
title: Compose file version 1 reference
---
These topics describe version 1 of the Compose file format. This is the oldest
version.
For a Compose/Docker Engine compatibility matrix, and detailed guidelines on
versions and upgrading, see
[Compose file versions and upgrading](compose-versioning.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 the [version 1 file format](compose-versioning.md#version-1), `build` is different in
> two ways:
>
> 1. Only the string form (`build: .`) is allowed - not the object form that is allowed in Version 2 and up.
> 2. 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:
>
> 1. It appears alongside `build`, not as a sub-option:
>
> 2. 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` 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.
### 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](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](#dependson), 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](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](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](index.md#networkmode) and [networks](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, oom_score_adj, 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](index.md)
- [Installing Compose](install.md)
- [Compose file versions and upgrading](compose-versioning.md)
- [Get started with Django](django.md)
- [Get started with Rails](rails.md)
- [Get started with WordPress](wordpress.md)
- [Command line reference](./reference/index.md)

1179
compose/compose-file/compose-file-v2.md Normal file
View File

File diff suppressed because it is too large Load Diff

318
compose/compose-file/compose-versioning.md Normal file
View File

@ -0,0 +1,318 @@
---
description: Compose file reference
keywords: fig, composition, compose, versions, upgrading, docker
title: Compose file versions and upgrading
---
The Compose file is a [YAML](http://yaml.org/) file defining services,
networks, and volumes for a Docker application.
Thes Compose file formats are now specified in these references, specific to each version.
- [Version 3](index.md) (most current, and recommended)
- [Version 2](compose-file-v2.md)
- [Version 1](compose-file-v1.md)
The topics below explain the differences among the versions, Docker Engine compatibility, and how to upgrade.
## Compatibility matrix
{% include content/compose-matrix.md %}
## 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'` 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](/engine/swarm/index.md). This is specified with a `version: '3'` or `version: '3.1'`, etc., entry at the root of the YAML.
The [Compatibility Matrix](#compatibility-matrix) shows Compose file versions mapped to Docker Engine releases.
To move your project to a later version, see the [Upgrading](#upgrading)
section.
> **Note:** If you're using
> [multiple Compose files](extends.md#different-environments) or
> [extending services](extends.md#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](index.md#service-configuration-reference) 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](index.md#volume-configuration-reference), [networks](index.md#network-configuration-reference) or
[build arguments](index.md#args).
Compose does not take advantage of [networking](index.md#networking.md) 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 will need to use
[links](compose-file-v1.md#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](compose-file-v2.md#service-configuration-reference)
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](compose-file-v2.md#volume-configuration-reference) can be declared under the
`volumes` key, and [networks](compose-file-v2.md#network-configuration-reference) 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](compose-file-v2.md#links) are largely unnecessary. For more details, see
[Networking in Compose](compose-file-v2.md#networking.md).
Simple example:
version: '2'
services:
web:
build: .
ports:
- "5000:5000"
volumes:
- .:/code
redis:
image: redis
A more extended example, defining volumes and networks:
version: '2'
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: '2'
services:
web:
build: .
depends_on:
- db
- redis
redis:
image: redis
db:
image: postgres
* ipv4_address, ipv6_address
[Variable substitution](compose-file-v2.md#variable-substitution) was added in Version 2.
### Version 2.1
An upgrade of [version 2](#version-2) that introduces new parameters only
available with Docker Engine version **1.12.0+**
Introduces the following additional parameters:
- [`link_local_ips`](compose-file-v2.md#linklocalips)
- [`isolation`](compose-file-v2.md#isolation)
- `labels` for [volumes](compose-file-v2.md#volume-configuration-reference) and
[networks](compose-file-v2.md#network-configuration-reference)
- [`userns_mode`](compose-file-v2.md#userns_mode)
- [`healthcheck`](compose-file-v2.md#healthcheck)
- [`sysctls`](compose-file-v2.md#sysctls)
### Version 3
Designed to be cross-compatible between Compose and the Docker Engine's
[swarm mode](/engine/swarm/index.md), version 3 removes several options and adds
several more.
- Removed: `volume_driver`, `volumes_from`, `cpu_shares`, `cpu_quota`, `cpuset`,
`mem_limit`, `memswap_limit`. See the [upgrading](#upgrading)
guide for how to migrate away from these.
- Added: [deploy](index.md#deploy)
## 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](index.md#volume-configuration-reference)
and specify the driver there.
version: "3"
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](index.md#volume-configuration-reference)
and reference it from each service that shares it using the
[service-level `volumes` option](index.md#volumes-volumedriver).
- `cpu_shares`, `cpu_quota`, `cpuset`, `mem_limit`, `memswap_limit`: These
have been replaced by the [resources](index.md#resources) key under
`deploy`. Note that `deploy` configuration only takes effect when using
`docker stack deploy`, and is ignored by `docker-compose`.
### 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](link-env-deprecated.md), 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](networking.md), or connect both the external container and
your service's containers to an
[external network](networking.md#using-a-pre-existing-network).
- `net`: This is now replaced by [network_mode](compose-file-v1.md#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: '2'
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
## Compose file format references
- [Compose file version 3](index.md)
- [Compose file version 2](compose-file-v2.md)
- [Compose file version 1](compose-file-v1.md)

577
compose/compose-file.md → compose/compose-file/index.md
View File

@ -3,13 +3,23 @@ description: Compose file reference
keywords: fig, composition, compose, docker
redirect_from:
- /compose/yml
title: Compose file reference
- /compose/compose-file-v3.md
title: Compose file version 3 reference
---
These topics describe version 3 of the Compose file format. This is the newest
version.
For a Compose/Docker Engine compatibility matrix, and detailed guidelines on
versions and upgrading, see
[Compose file versions and upgrading](compose-versioning.md).
## Service configuration reference
The Compose file is a [YAML](http://yaml.org/) file defining
[services](compose-file.md#service-configuration-reference),
[networks](compose-file.md#network-configuration-reference) and
[volumes](compose-file.md#volume-configuration-reference).
[services](#service-configuration-reference),
[networks](#network-configuration-reference) and
[volumes](#volume-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.
@ -24,18 +34,11 @@ As with `docker run`, options specified in the Dockerfile (e.g., `CMD`,
specify them again in `docker-compose.yml`.
You can use environment variables in configuration values with a Bash-like
`${VARIABLE}` syntax - see [variable substitution](compose-file.md#variable-substitution) for
full details.
## Service configuration reference
> **Note:** There are several versions of the Compose file format – 1, 2, 2.1
> and 3. For more information, see the [Versioning](compose-file.md#versioning)
> section.
`${VARIABLE}` syntax - see [variable
substitution](compose-file.md#variable-substitution) for full details.
This section contains a list of all configuration options supported by a service
definition.
definition in version 3.
### build
@ -61,22 +64,12 @@ with the `webapp` and optional `tag` specified in `image`:
This will result in an image named `webapp` and tagged `tag`, built from `./dir`.
> **Note**: In the [version 1 file format](compose-file.md#version-1), `build` is different in
> two ways:
>
> 1. Only the string form (`build: .`) is allowed - not the object form.
> 2. Using `build` together with `image` is not allowed. Attempting to do so
> results in an error.
> **Note:** This option is ignored when
> [deploying a stack in swarm mode](/engine/reference/commandline/stack_deploy.md)
> with a (version 3) Compose file. The `docker stack` command accepts only pre-built images.
#### context
> [Version 2 file format](compose-file.md#version-2) and up. In version 1, just use
> [build](compose-file.md#build).
Either a path to a directory containing a Dockerfile, or a url to a git repository.
When the value supplied is a relative path, it is interpreted as relative to the
@ -99,22 +92,8 @@ specified.
context: .
dockerfile: Dockerfile-alternate
> **Note**: In the [version 1 file format](compose-file.md#version-1), `dockerfile` is
> different in two ways:
>
> 1. It appears alongside `build`, not as a sub-option:
>
> ```
> build: .
> dockerfile: Dockerfile-alternate
> ```
>
> 2. Using `dockerfile` together with `image` is not allowed. Attempting to do so results in an error.
#### args
> [Version 2 file format](compose-file.md#version-2) and up.
Add build arguments, which are environment variables accessible only during the
build process.
@ -200,7 +179,7 @@ results in an error.
### deploy
> **[Version 3](compose-file.md#version-3) only.**
> **[Version 3](compose-versioning.md#version-3) only.**
Specify configuration related to the deployment and running of services. This
only takes effect when deploying to a [swarm](/engine/swarm/index.md) with
@ -268,13 +247,18 @@ Configures resource constraints. This replaces the older resource constraint
options in Compose files prior to version 3 (`cpu_shares`, `cpu_quota`,
`cpuset`, `mem_limit`, `memswap_limit`).
resources:
limits:
cpus: '0.001'
memory: 50M
reservations:
cpus: '0.0001'
memory: 20M
Each of these is a single value, analogous to its
[docker run](/engine/reference/run.md) counterpart.
```
resources:
limits:
cpus: '0.001'
memory: 50M
reservations:
cpus: '0.0001'
memory: 20M
```
#### restart_policy
@ -362,9 +346,7 @@ Simple example:
> for a service to be ready, see [Controlling startup order](startup-order.md)
> for more on this problem and strategies for solving it.
> **[Version 2.1](compose-file.md#version-21) file format only.**
With Compose 1.10, it is now possible to indicate you want a dependency to wait
A healthcheck indicates you want a dependency to wait
for another container to be "healthy" (i.e. its healthcheck advertises a
successful state) before starting.
@ -389,7 +371,7 @@ Example:
In the above example, Compose will wait for the `redis` service to be started
(legacy behavior) and the `db` service to be healthy before starting `web`.
See the [healthcheck section](compose-file.md#healthcheck) for complementary
See the [healthcheck section](#healthcheck) for complementary
information.
### dns
@ -420,7 +402,7 @@ Custom DNS search domains. Can be a single value or a list.
### tmpfs
> [Version 2 file format](compose-file.md#version-2) and up.
> [Version 2 file format](compose-versioning.md#version-2) and up.
Mount a temporary file system inside the container. Can be a single value or a list.
@ -565,9 +547,9 @@ container name and the link alias (`CONTAINER:ALIAS`).
- project_db_1:mysql
- project_db_1:postgresql
> **Note:** If you're using the [version 2 file format](compose-file.md#version-2), the
> **Note:** If you're using the [version 2 or above file format](compose-versioning.md#version-2), the
> externally-created containers must be connected to at least one of the same
> networks as the service which is linking to them.
> networks as the service which is linking to them. Starting with Version 2, links are a legacy option. We recommend using networks instead. See [Version 2 file format](compose-versioning.md#version-2).
> **Note:** This option is ignored when
> [deploying a stack in swarm mode](/engine/reference/commandline/stack_deploy.md)
@ -588,7 +570,7 @@ An entry with the ip address and hostname will be created in `/etc/hosts` inside
### group_add
> [Version 2 file format](compose-file.md#version-2) and up.
> [Version 2 file format](compose-versioning.md#version-2) and up.
Specify additional groups (by name or number) which the user inside the
container will be a member of. Groups must exist in both the container and the
@ -661,13 +643,8 @@ If the image does not exist, Compose attempts to pull it, unless you have also
specified [build](compose-file.md#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-file.md#version-1), using `build` together
> with `image` is not allowed. Attempting to do so results in an error.
### isolation
> [Added in version 2.1 file format](compose-file.md#version-21).
Specify a container’s isolation technology. On Linux, the only supported value
is `default`. On Windows, acceptable values are `default`, `process` and
`hyperv`. Refer to the
@ -676,7 +653,6 @@ for details.
### 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.
@ -718,9 +694,6 @@ Links also express dependency between services in the same way as
### logging
> [Version 2 file format](compose-file.md#version-2) and up. In version 1, use
> [log_driver](compose-file.md#log_driver) and [log_opt](compose-file.md#log_opt).
Logging configuration for the service.
logging:
@ -750,43 +723,8 @@ Logging options are key-value pairs. An example of `syslog` options:
options:
syslog-address: "tcp://192.168.0.42:123"
### log_driver
> [Version 1 file format](compose-file.md#version-1) only. In version 2, use
> [logging](compose-file.md#logging).
Specify a log driver. The default is `json-file`.
log_driver: syslog
### log_opt
> [Version 1 file format](compose-file.md#version-1) only. In version 2, use
> [logging](compose-file.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-file.md#version-1) only. In version 2, use
> [network_mode](compose-file.md#networkmode).
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]"
### network_mode
> [Version 2 file format](compose-file.md#version-2) and up. In version 1, use [net](compose-file.md#net).
Network mode. Use the same values as the docker client `--net` parameter, plus
the special form `service:[service name]`.
@ -802,8 +740,6 @@ the special form `service:[service name]`.
### networks
> [Version 2 file format](compose-file.md#version-2) and up. In version 1, use [net](compose-file.md#net).
Networks to join, referencing entries under the
[top-level `networks` key](compose-file.md#network-configuration-reference).
@ -896,8 +832,6 @@ An example:
#### link_local_ips
> [Added in version 2.1 file format](compose-file.md#version-21).
Specify a list of link-local IPs. Link-local IPs are special IPs which belong
to a well known subnet and are purely managed by the operator, usually
dependent on the architecture where they are deployed. Therefore they are not
@ -962,8 +896,6 @@ Override the default labeling scheme for each container.
### stop_grace_period
> [Added in version 2 file format](compose-file.md#version-2)
Specify how long to wait when attempting to stop a container if it doesn't
handle SIGTERM (or whatever stop signal has been specified with
[`stop_signal`](compose-file.md#stopsignal)), before sending SIGKILL. Specified
@ -989,8 +921,6 @@ SIGTERM. Setting an alternative signal using `stop_signal` will cause
### sysctls
> [Added in version 2.1 file format](compose-file.md#version-21).
Kernel parameters to set in the container. You can use either an array or a
dictionary.
@ -1020,8 +950,6 @@ limit as an integer or soft/hard limits as a mapping.
### userns_mode
> [Added in version 2.1 file format](compose-file.md#version-21).
userns_mode: "host"
Disables the user namespace for this service, if Docker daemon is configured with user namespaces.
@ -1034,11 +962,15 @@ more information.
### volumes, volume\_driver
> **Note:** The top-level
> [`volumes` option](compose-file.md#volume-configuration-reference) defines
> a named volume and references it from each service's `volumes` list. This replaces `volumes_from` in earlir versions of the Compose file format.
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-file.md#version-2), named volumes need to be specified with the
[top-level `volumes` key](compose-file.md#volume-configuration-reference).
When using [version 1](compose-file.md#version-1), the Docker Engine will create the named
For [version 2 files](compose-versioning.md#version-2), named volumes need to be specified with the
[top-level `volumes` key](#volume-configuration-reference).
When using [version 1](compose-versioning.md#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
@ -1066,24 +998,14 @@ 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-file.md#versioning) you're using:
[Compose file version](compose-versioning.md#versioning) you're using:
- `volume_driver` is not supported at all in
[version 3](compose-file.md#version-3). Instead of setting the volume driver
[version 3](compose-versioning.md#version-3). Instead of setting the volume driver
on the service, define a volume using the
[top-level `volumes` option](compose-file.md#volume-configuration-reference)
[top-level `volumes` option](#volume-configuration-reference)
and specify the driver there.
- You can use `volume_driver` in [version 2 files](compose-file.md#version-2),
but it will only apply to anonymous volumes (those specified in the image,
or specified under `volumes` without an explicit named volume or host path).
To configure the driver for a named volume, use the `driver` key under the
entry in the
[top-level `volumes` option](compose-file.md#volume-configuration-reference).
- For [version 1 files](compose-file.md#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.
@ -1091,79 +1013,6 @@ There are several things to note, depending on which
See [Docker Volumes](/engine/userguide/dockervolumes.md) and
[Volume Plugins](/engine/extend/plugins_volume.md) for more information.
### volumes_from
> **Removed in [version 3](compose-file.md#version-3).** The best way to share a
> volume between services is to use the top-level
> [`volumes` option](compose-file.md#volume-configuration-reference) to define
> a named volume and reference it from each service's `volumes` list.
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
- container:container_name
- container:container_name:rw
> **Note:** The `container:...` formats are only supported in the
> [version 2 file format](compose-file.md#version-2). In [version 1](compose-file.md#version-1), you can use
> container names without marking them as such:
>
> - service_name
> - service_name:ro
> - container_name
> - container_name:rw
### cpu\_shares, cpu\_quota, cpuset, domainname, hostname, ipc, mac\_address, mem\_limit, memswap\_limit, oom_score_adj, privileged, read\_only, restart, shm\_size, stdin\_open, tty, user, working\_dir
> **Note:** Resource constraint options (`cpu_shares`, `cpu_quota`, `cpuset`,
> `mem_limit`, `memswap_limit`) have been removed in
> [version 3](compose-file.md#version-3). You should set resource constraints
> with [deploy.resources](compose-file.md#resources) instead. Note that `deploy`
> configuration only takes effect when using `docker stack deploy`, and is
> ignored by `docker-compose`.
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
oom_score_adj: 500
restart: always
read_only: true
shm_size: 64M
stdin_open: true
tty: true
> **Note:** The following options are only available for
> [version 2](compose-file.md#version-2) and up:
> * `oom_score_adj`
> **Note:** The `domainname`, `ipc`, `mac_address`, `privileged`, `read_only`,
> `restart` and `shm_size` options are ignored when
> [deploying a stack in swarm mode](/engine/reference/commandline/stack_deploy.md)
> with a (version 3) Compose file.
## Specifying durations
Some configuration options, such as the `interval` and `timeout` sub-options for
@ -1265,8 +1114,6 @@ refer to it within the Compose file:
### labels
> [Added in version 2.1 file format](compose-file.md#version-21).
Add metadata to containers using
[Docker labels](/engine/userguide/labels-custom-metadata.md). You can use either
an array or a dictionary.
@ -1315,8 +1162,6 @@ documentation for more information. Optional.
### enable_ipv6
> [Added in version 2.1 file format](compose-file.md#version-21).
Enable IPv6 networking on this network.
### ipam
@ -1348,16 +1193,12 @@ A full example:
### internal
> [Version 2 file format](compose-file.md#version-2) and up.
By default, Docker also connects a bridge network to it to provide external
connectivity. If you want to create an externally isolated overlay network,
you can set this option to `true`.
### labels
> [Added in version 2.1 file format](compose-file.md#version-21).
Add metadata to containers using
[Docker labels](/engine/userguide/labels-custom-metadata.md). You can use either
an array or a dictionary.
@ -1414,336 +1255,16 @@ refer to it within the Compose file:
external:
name: actual-name-of-network
## Versioning
There are currently four 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. This is specified with a `version: '2'` entry at the root of the
YAML.
- Version 2.1, an upgrade over version 2 that takes advantage of newer Docker
Engine features. Specify with a `version: '2.1'` entry at the root of
the YAML.
- Version 3, the latest and recommended version, designed to be cross-compatible
between Compose and the Docker Engine's [swarm mode](/engine/swarm/index.md).
To move your project to a later version, see the
[Upgrading](compose-file.md#upgrading) section.
> **Note:** If you're using
> [multiple Compose files](extends.md#different-environments) or
> [extending services](extends.md#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](compose-file.md#service-configuration-reference) 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](compose-file.md#volume-configuration-reference), [networks](networking.md) or
[build arguments](compose-file.md#args).
Compose does not take advantage of [networking](networking.md) 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 will need to use
[links](compose-file.md#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](compose-file.md#service-configuration-reference)
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](compose-file.md#volume-configuration-reference) can be declared under the
`volumes` key, and [networks](compose-file.md#network-configuration-reference) 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](compose-file.md#links) are largely unnecessary. For more details, see
[Networking in Compose](networking.md).
Simple example:
version: '2'
services:
web:
build: .
ports:
- "5000:5000"
volumes:
- .:/code
redis:
image: redis
A more extended example, defining volumes and networks:
version: '2'
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
### Version 2.1
An upgrade of [version 2](compose-file.md#version-2) that introduces new parameters only
available with Docker Engine version **1.12.0+**
Introduces the following additional parameters:
- [`link_local_ips`](compose-file.md#linklocalips)
- [`isolation`](compose-file.md#isolation)
- `labels` for [volumes](compose-file.md#volume-configuration-reference) and
[networks](compose-file.md#network-configuration-reference)
- [`userns_mode`](compose-file.md#userns_mode)
- [`healthcheck`](compose-file.md#healthcheck),
- [`sysctls`](compose-file.md#sysctls)
### Version 3
Designed to be cross-compatible between Compose and the Docker Engine's
[swarm mode](/engine/swarm/index.md), version 3 removes several options and adds
several more.
- Removed: `volume_driver`, `volumes_from`, `cpu_shares`, `cpu_quota`, `cpuset`,
`mem_limit`, `memswap_limit`. See the [upgrading](compose-file.md#upgrading)
guide for how to migrate away from these.
- Added: [deploy](compose-file.md#deploy)
### 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](compose-file.md#volume-configuration-reference)
and specify the driver there.
version: "3"
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](compose-file.md#volume-configuration-reference)
and reference it from each service that shares it using the
[service-level `volumes` option](compose-file.md#volumes-volume-driver).
- `cpu_shares`, `cpu_quota`, `cpuset`, `mem_limit`, `memswap_limit`: These
have been replaced by the [resources](compose-file.md#resources) key under
`deploy`. Note that `deploy` configuration only takes effect when using
`docker stack deploy`, and is ignored by `docker-compose`.
#### 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](link-env-deprecated.md), 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](networking.md), or connect both the external container and
your service's containers to an
[external network](networking.md#using-a-pre-existing-network).
- `net`: This is now replaced by [network_mode](compose-file.md#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: '2'
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
## Variable substitution
Your configuration options can contain environment variables. Compose uses the
variable values from the shell environment in which `docker-compose` is run.
For example, suppose the shell contains `EXTERNAL_PORT=8000` and you supply
this configuration:
web:
build: .
ports:
- "${EXTERNAL_PORT}:5000"
When you run `docker-compose up` with this configuration, Compose looks for
the `EXTERNAL_PORT` environment variable in the shell and substitutes its
value in. In this example, Compose resolves the port mapping to `"8000:5000"`
before creating the `web` container.
If an environment variable is not set, Compose substitutes with an empty
string. In the example above, if `EXTERNAL_PORT` is not set, the value for the
port mapping is `:5000` (which is of course an invalid port mapping, and will
result in an error when attempting to create the container).
You can set default values for environment variables using a
[`.env` file](env-file.md), which Compose will automatically look for. Values
set in the shell environment will override those set in the `.env` file.
$ unset EXTERNAL_PORT
$ echo "EXTERNAL_PORT=6000" > .env
$ docker-compose up # EXTERNAL_PORT will be 6000
$ export EXTERNAL_PORT=7000
$ docker-compose up # EXTERNAL_PORT will be 7000
Both `$VARIABLE` and `${VARIABLE}` syntax are supported.
Additionally when using the [2.1 file format](compose-file.md#version-21), it
is possible to provide inline default values using typical shell syntax:
- `${VARIABLE:-default}` will evaluate to `default` if `VARIABLE` is unset or
empty in the environment.
- `${VARIABLE-default}` will evaluate to `default` only if `VARIABLE` is unset
in the environment.
Other extended shell-style features, such as `${VARIABLE/foo/bar}`, are not
supported.
You can use a `$$` (double-dollar sign) when your configuration needs a literal
dollar sign. This also prevents Compose from interpolating a value, so a `$$`
allows you to refer to environment variables that you don't want processed by
Compose.
web:
build: .
command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
If you forget and use a single dollar sign (`$`), Compose interprets the value as an environment variable and will warn you:
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.
{% include content/compose-var-sub.md %}
## Compose documentation
- [User guide](index.md)
- [Installing Compose](install.md)
- [Compose file versions and upgrading](compose-versioning.md)
- [Sample app with swarm mode](/engine/getstarted-voting-app/)
- [Get started with Django](django.md)
- [Get started with Rails](rails.md)
- [Get started with WordPress](wordpress.md)