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---
description: Compose file reference
keywords: fig, composition, compose version 2, docker
title: Compose file version 2 reference
toc_max: 4
toc_min: 1
---
{% include compose-eol.md %}
## Reference and guidelines
These topics describe version 2 of the Compose file format.
## 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 Compose file is a [YAML](https://yaml.org) file defining
[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.
A service definition contains configuration that is applied to each
container started for that service, much like passing command-line parameters to
`docker run`. Likewise, network and volume definitions are analogous to
`docker network create` and `docker volume create`.
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`.
You can use environment variables in configuration values with a Bash-like
`${VARIABLE}` syntax - see [variable substitution](#variable-substitution) for
full details.
This section contains a list of all configuration options supported by a service
definition in version 2.
### blkio_config
A set of configuration options to set block IO limits for this service.
version: "{{ site.compose_file_v2 }}"
services:
foo:
image: busybox
blkio_config:
weight: 300
weight_device:
- path: /dev/sda
weight: 400
device_read_bps:
- path: /dev/sdb
rate: '12mb'
device_read_iops:
- path: /dev/sdb
rate: 120
device_write_bps:
- path: /dev/sdb
rate: '1024k'
device_write_iops:
- path: /dev/sdb
rate: 30
#### device_read_bps, device_write_bps
Set a limit in bytes per second for read / write operations on a given device.
Each item in the list must have two keys:
* `path`, defining the symbolic path to the affected device
* `rate`, either as an integer value representing the number of bytes or as
a string expressing a [byte value](#specifying-byte-values).
#### device_read_iops, device_write_iops
Set a limit in operations per second for read / write operations on a given
device. Each item in the list must have two keys:
* `path`, defining the symbolic path to the affected device
* `rate`, as an integer value representing the permitted number of operations
per second.
#### weight
Modify the proportion of bandwidth allocated to this service relative to other
services. Takes an integer value between 10 and 1000, with 500 being the
default.
#### weight_device
Fine-tune bandwidth allocation by device. Each item in the list must have
two keys:
* `path`, defining the symbolic path to the affected device
* `weight`, an integer value between 10 and 1000
### build
Configuration options that are applied at build time.
`build` can be specified either as a string containing a path to the build
context:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
webapp:
build: ./dir
```
Or, as an object with the path specified under [context](#context) and
optionally [Dockerfile](#dockerfile) and [args](#args):
```yaml
version: "{{ site.compose_file_v2 }}"
services:
webapp:
build:
context: ./dir
dockerfile: Dockerfile-alternate
args:
buildno: 1
```
If you specify `image` as well as `build`, then Compose names the built image
with the `webapp` and optional `tag` specified in `image`:
```yaml
build: ./dir
image: webapp:tag
```
This results in an image named `webapp` and tagged `tag`, built from `./dir`.
#### context
> Added in [version 2.0](compose-versioning.md#version-2) file format.
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
location of the Compose file. This directory is also the build context that is
sent to the Docker daemon.
Compose builds and tags it with a generated name, and uses that image
thereafter.
```yaml
build:
context: ./dir
```
#### dockerfile
Alternate Dockerfile.
Compose uses an alternate file to build with. A build path must also be
specified.
```yaml
build:
context: .
dockerfile: Dockerfile-alternate
```
#### args
> Added in [version 2.0](compose-versioning.md#version-2) file format.
Add build arguments, which are environment variables accessible only during the
build process.
First, specify the arguments in your Dockerfile:
```dockerfile
# syntax=docker/dockerfile:1
ARG buildno
ARG gitcommithash
RUN echo "Build number: $buildno"
RUN echo "Based on commit: $gitcommithash"
```
Then specify the arguments under the `build` key. You can pass a mapping
or a list:
```yaml
build:
context: .
args:
buildno: 1
gitcommithash: cdc3b19
```
```yaml
build:
context: .
args:
- buildno=1
- gitcommithash=cdc3b19
```
> Scope of build-args
>
> In your Dockerfile, if you specify `ARG` before the `FROM` instruction,
> `ARG` is not available in the build instructions under `FROM`.
> If you need an argument to be available in both places, also specify it under
> the `FROM` instruction. Refer to the [understand how ARGS and FROM interact](../../engine/reference/builder.md#understand-how-arg-and-from-interact)
> section in the documentation for usage details.
You can omit the value when specifying a build argument, in which case its value
at build time is the value in the environment where Compose is running.
```yaml
args:
- buildno
- gitcommithash
```
> Tip when using boolean values
>
> YAML boolean values (`"true"`, `"false"`, `"yes"`, `"no"`, `"on"`,
> `"off"`) must be enclosed in quotes, so that the parser interprets them as
> strings.
#### cache_from
> Added in [version 2.2](compose-versioning.md#version-22) file format
A list of images that the engine uses for cache resolution.
```yaml
build:
context: .
cache_from:
- alpine:latest
- corp/web_app:3.14
```
#### extra_hosts
Add hostname mappings at build-time. Use the same values as the docker client `--add-host` parameter.
```yaml
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 build, e.g:
```console
162.242.195.82 somehost
50.31.209.229 otherhost
```
#### isolation
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Specify a build’s container isolation technology. On Linux, the only supported value
is `default`. On Windows, acceptable values are `default`, `process` and
`hyperv`. Refer to the
[Docker Engine docs](../../engine/reference/commandline/run.md#isolation)
for details.
If unspecified, Compose will use the `isolation` value found in the service's definition
to determine the value to use for builds.
#### labels
> Added in [version 2.1](compose-versioning.md#version-21) file format
Add metadata to the resulting image using [Docker labels](../../config/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.
```yaml
build:
context: .
labels:
com.example.description: "Accounting webapp"
com.example.department: "Finance"
com.example.label-with-empty-value: ""
```
```yaml
build:
context: .
labels:
- "com.example.description=Accounting webapp"
- "com.example.department=Finance"
- "com.example.label-with-empty-value"
```
#### network
> Added in [version 2.2](compose-versioning.md#version-22) file format
Set the network containers connect to for the `RUN` instructions during
build.
```yaml
build:
context: .
network: host
```
```yaml
build:
context: .
network: custom_network_1
```
Use `none` to disable networking during build:
```yaml
build:
context: .
network: none
```
#### shm_size
> Added in [version 2.3](compose-versioning.md#version-23) file format
Set the size of the `/dev/shm` partition for this build's containers. Specify
as an integer value representing the number of bytes or as a string expressing
a [byte value](#specifying-byte-values).
```yaml
build:
context: .
shm_size: '2gb'
```
```yaml
build:
context: .
shm_size: 10000000
```
#### target
> Added in [version 2.3](compose-versioning.md#version-23) file format
Build the specified stage as defined inside the `Dockerfile`. See the
[multi-stage build docs](../../build/building/multi-stage.md) for
details.
```yaml
build:
context: .
target: prod
```
### cap_add, cap_drop
Add or drop container capabilities.
See `man 7 capabilities` for a full list.
```yaml
cap_add:
- ALL
cap_drop:
- NET_ADMIN
- SYS_ADMIN
```
### cgroup_parent
Specify an optional parent cgroup for the container.
```yaml
cgroup_parent: m-executor-abcd
```
### command
Override the default command.
```yaml
command: bundle exec thin -p 3000
```
The command can also be a list, in a manner similar to
[dockerfile](../../engine/reference/builder.md#cmd):
```yaml
command: ["bundle", "exec", "thin", "-p", "3000"]
```
### container_name
Specify a custom container name, rather than a generated default name.
```yaml
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.
### cpu_rt_runtime, cpu_rt_period
> Added in [version 2.2](compose-versioning.md#version-22) file format
Configure CPU allocation parameters using the Docker daemon realtime scheduler.
```yaml
cpu_rt_runtime: '400ms'
cpu_rt_period: '1400us'
```
Integer values will use microseconds as units:
```yaml
cpu_rt_runtime: 95000
cpu_rt_period: 11000
```
### device_cgroup_rules
> Added in [version 2.3](compose-versioning.md#version-23) file format.
Add rules to the cgroup allowed devices list.
```yaml
device_cgroup_rules:
- 'c 1:3 mr'
- 'a 7:* rmw'
```
### devices
List of device mappings. Uses the same format as the `--device` docker
client create option.
```yaml
devices:
- "/dev/ttyUSB0:/dev/ttyUSB0"
```
### depends_on
> Added in [version 2.0](compose-versioning.md#version-2) file format.
Express dependency between services. Service dependencies cause the following
behaviors:
- `docker-compose up` starts services in dependency order. In the following
example, `db` and `redis` are started before `web`.
- `docker-compose up SERVICE` automatically includes `SERVICE`'s
dependencies. In the example below, `docker-compose up web` also
creates and starts `db` and `redis`.
- `docker-compose stop` stops services in dependency order. In the following
example, `web` is stopped before `db` and `redis`.
Simple example:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
web:
build: .
depends_on:
- db
- redis
redis:
image: redis
db:
image: postgres
```
> **Note**
>
> `depends_on` does not wait for `db` and `redis` to be "ready" before
> starting `web` - only until they have been started. If you need to wait
> for a service to be ready, see [Controlling startup order](../startup-order.md)
> for more on this problem and strategies for solving it.
> Added in [version 2.1](compose-versioning.md#version-21) file format.
A healthcheck indicates that you want a dependency to wait
for another container to be "healthy" (as indicated by a successful state from
the healthcheck) before starting.
Example:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
web:
build: .
depends_on:
db:
condition: service_healthy
redis:
condition: service_started
redis:
image: redis
db:
image: postgres
healthcheck:
test: "exit 0"
```
In the above example, Compose waits for the `redis` service to be started
(legacy behavior) and the `db` service to be healthy before starting `web`.
See the [healthcheck section](#healthcheck) for complementary
information.
### dns
Custom DNS servers. Can be a single value or a list.
```yaml
dns: 8.8.8.8
```
```yaml
dns:
- 8.8.8.8
- 9.9.9.9
```
### dns_opt
List of custom DNS options to be added to the container's `resolv.conf` file.
```yaml
dns_opt:
- use-vc
- no-tld-query
```
### dns_search
Custom DNS search domains. Can be a single value or a list.
```yaml
dns_search: example.com
```
```yaml
dns_search:
- dc1.example.com
- dc2.example.com
```
### entrypoint
Override the default entrypoint.
```yaml
entrypoint: /code/entrypoint.sh
```
The entrypoint can also be a list, in a manner similar to
[dockerfile](../../engine/reference/builder.md#entrypoint):
```yaml
entrypoint: ["php", "-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 declared in the [environment](#environment) section
_override_ these values – this holds true even if those values are
empty or undefined.
```yaml
env_file: .env
```
```yaml
env_file:
- ./common.env
- ./apps/web.env
- /opt/runtime_opts.env
```
Compose expects each line in an env file to be in `VAR=VAL` format. Lines
beginning with `#` are treated as comments and are ignored. Blank lines are
also ignored.
```console
# Set Rails/Rack environment
RACK_ENV=development
```
> **Note**
>
> If your service specifies a [build](#build) option, variables defined in
> environment files are _not_ automatically visible during the build. Use
> the [args](#args) sub-option of `build` to define build-time environment
> variables.
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`:
```yaml
services:
some-service:
env_file:
- a.env
- b.env
```
And the following files:
```console
# a.env
VAR=1
```
and
```console
# 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.
```yaml
environment:
RACK_ENV: development
SHOW: 'true'
SESSION_SECRET:
```
```yaml
environment:
- RACK_ENV=development
- SHOW=true
- SESSION_SECRET
```
> **Note**
>
> If your service specifies a [build](#build) option, variables defined in
> `environment` are _not_ automatically visible during the build. Use the
> [args](#args) sub-option of `build` to define build-time environment
> variables.
### 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.
```yaml
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.
```yaml
extends:
file: common.yml
service: webapp
```
The `service` is 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 the legacy option `links` when
specifying both the container name and the link alias (`CONTAINER:ALIAS`).
```yaml
external_links:
- redis_1
- project_db_1:mysql
- project_db_1:postgresql
```
> **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 that is linking to them. [Links](compose-file-v2.md#links)
> are a legacy option. We recommend using [networks](#networks) instead.
### extra_hosts
Add hostname mappings. Use the same values as the docker client `--add-host` parameter.
```yaml
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:
```console
162.242.195.82 somehost
50.31.209.229 otherhost
```
### group_add
Specify additional groups (by name or number) which the user inside the
container should be a member of. Groups must exist in both the container and the
host system to be added. An example of where this is useful is when multiple
containers (running as different users) need to all read or write the same
file on the host system. That file can be owned by a group shared by all the
containers, and specified in `group_add`. See the
[Docker documentation](../../engine/reference/run.md#additional-groups) for more
details.
A full example:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
myservice:
image: alpine
group_add:
- mail
```
Running `id` inside the created container shows that the user belongs to
the `mail` group, which would not have been the case if `group_add` were not
used.
### healthcheck
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Configure a check that's run to determine whether or not containers for this
service are "healthy". See the docs for the
[HEALTHCHECK Dockerfile instruction](../../engine/reference/builder.md#healthcheck)
for details on how healthchecks work.
```yaml
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost"]
interval: 1m30s
timeout: 10s
retries: 3
start_period: 40s
```
`interval`, `timeout` and `start_period` are specified as
[durations](#specifying-durations).
> Added in [version 2.3](compose-versioning.md#version-23) file format.
>
> The `start_period` option was added in file format 2.3.
`test` must be either a string or a list. If it's a list, the first item must be
either `NONE`, `CMD` or `CMD-SHELL`. If it's a string, it's equivalent to
specifying `CMD-SHELL` followed by that string.
```yaml
# Hit the local web app
test: ["CMD", "curl", "-f", "http://localhost"]
```
As above, but wrapped in `/bin/sh`. Both forms below are equivalent.
```yaml
test: ["CMD-SHELL", "curl -f http://localhost || exit 1"]
```
```yaml
test: curl -f https://localhost || exit 1
```
To disable any default healthcheck set by the image, you can use `disable: true`.
This is equivalent to specifying `test: ["NONE"]`.
```yaml
healthcheck:
disable: true
```
### image
Specify the image to start the container from. Can either be a repository/tag or
a partial image ID.
```yaml
image: redis
```
```yaml
image: ubuntu:18.04
```
```yaml
image: tutum/influxdb
```
```yaml
image: example-registry.com:4000/postgresql
```
```yaml
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.
### init
> Added in [version 2.2](compose-versioning.md#version-22) file format.
Run an init inside the container that forwards signals and reaps processes.
Set this option to `true` to enable this feature for the service.
```yaml
version: "{{ site.compose_file_v2 }}"
services:
web:
image: alpine:latest
init: true
```
> The default init binary that is used is [Tini](https://github.com/krallin/tini),
> and is installed in `/usr/libexec/docker-init` on the daemon host. You can
> configure the daemon to use a custom init binary through the
> [`init-path` configuration option](../../engine/reference/commandline/dockerd.md#daemon-configuration-file).
### isolation
> Added in [version 2.1](compose-versioning.md#version-21) file format.
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
[Docker Engine docs](../../engine/reference/commandline/run.md#isolation)
for details.
### labels
Add metadata to containers using [Docker labels](../../config/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.
```yaml
labels:
com.example.description: "Accounting webapp"
com.example.department: "Finance"
com.example.label-with-empty-value: ""
```
```yaml
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](#networks) instead.
```yaml
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 are not required to enable services to communicate - by default,
any service can reach any other service at that service’s name. (See also, the
[Links topic in Networking in Compose](../networking.md#link-containers).)
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 to
> communicate. We recommend using networks instead.
### logging
Logging configuration for the service.
```yaml
logging:
driver: syslog
options:
syslog-address: "tcp://192.168.0.42:123"
```
The `driver` name specifies a logging driver for the service's
containers, as with the ``--log-driver`` option for docker run
([documented here](../../config/containers/logging/configure.md)).
The default value is json-file.
```yaml
driver: "json-file"
```
```yaml
driver: "syslog"
```
```yaml
driver: "none"
```
> **Note**
>
> Only the `json-file` and `journald` drivers make the logs available directly
> from `docker-compose up` and `docker-compose logs`. Using any other driver
> does not print any logs.
Specify logging options for the logging driver with the ``options`` key, as with the ``--log-opt`` option for `docker run`.
Logging options are key-value pairs. An example of `syslog` options:
```yaml
driver: "syslog"
options:
syslog-address: "tcp://192.168.0.42:123"
```
### network_mode
> Changed in [version 2](compose-versioning.md#version-2) file format.
Network mode. Use the same values as the docker client `--network` parameter, plus
the special form `service:[service name]`.
```yaml
network_mode: "bridge"
```
```yaml
network_mode: "host"
```
```yaml
network_mode: "none"
```
```yaml
network_mode: "service:[service name]"
```
```yaml
network_mode: "container:[container name/id]"
```
### networks
> Changed in [version 2](compose-versioning.md#version-2) file format.
Networks to join, referencing entries under the
[top-level `networks` key](#network-configuration-reference).
```yaml
services:
some-service:
networks:
- some-network
- other-network
```
#### aliases
Aliases (alternative hostnames) for this service on the network. Other containers on the same network can use either the service name or this alias to connect to one of the service's containers.
Since `aliases` is network-scoped, the same service can have different aliases on different networks.
> **Note**
>
> A network-wide alias can be shared by multiple containers, and even by multiple
> services. If it is, then exactly which container the name resolves to is not
> guaranteed.
The general format is shown here.
```yaml
services:
some-service:
networks:
some-network:
aliases:
- alias1
- alias3
other-network:
aliases:
- alias2
```
In the example below, three services are provided (`web`, `worker`, and `db`),
along with two networks (`new` and `legacy`). The `db` service is reachable at
the hostname `db` or `database` on the `new` network, and at `db` or `mysql` on
the `legacy` network.
```yaml
version: "{{ site.compose_file_v2 }}"
services:
web:
image: "nginx:alpine"
networks:
- new
worker:
image: "my-worker-image:latest"
networks:
- legacy
db:
image: mysql
networks:
new:
aliases:
- database
legacy:
aliases:
- mysql
networks:
new:
legacy:
```
#### ipv4_address, ipv6_address
Specify a static IP address for containers for this service when joining the network.
The corresponding network configuration in the
[top-level networks section](#network-configuration-reference) must have an
`ipam` block with subnet and gateway configurations covering each static address.
> If IPv6 addressing is desired, the [`enable_ipv6`](#enable_ipv6) option must be set.
An example:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
app:
image: busybox
command: ifconfig
networks:
app_net:
ipv4_address: 172.16.238.10
ipv6_address: 2001:3984:3989::10
networks:
app_net:
driver: bridge
enable_ipv6: true
ipam:
driver: default
config:
- subnet: 172.16.238.0/24
gateway: 172.16.238.1
- subnet: 2001:3984:3989::/64
gateway: 2001:3984:3989::1
```
#### link_local_ips
> Added in [version 2.1](compose-versioning.md#version-21) file format.
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
managed by docker (IPAM driver).
Example usage:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
app:
image: busybox
command: top
networks:
app_net:
link_local_ips:
- 57.123.22.11
- 57.123.22.13
networks:
app_net:
driver: bridge
```
#### priority
Specify a priority to indicate in which order Compose should connect the
service's containers to its networks. If unspecified, the default value is `0`.
In the following example, the `app` service connects to `app_net_1` first
as it has the highest priority. It then connects to `app_net_3`, then
`app_net_2`, which uses the default priority value of `0`.
```yaml
version: "{{ site.compose_file_v2 }}"
services:
app:
image: busybox
command: top
networks:
app_net_1:
priority: 1000
app_net_2:
app_net_3:
priority: 100
networks:
app_net_1:
app_net_2:
app_net_3:
```
> **Note**
>
> If multiple networks have the same priority, the connection order is undefined.
### pid
```yaml
pid: "host"
```
```yaml
pid: "container:custom_container_1"
```
```yaml
pid: "service:foobar"
```
If set to one of the following forms: `container:<container_name>`,
`service:<service_name>`, the service shares the PID address space of the
designated container or service.
If set to "host", the service's PID mode is 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.
> Added in [version 2.1](compose-versioning.md#version-21) file format.
>
> The `service:` and `container:` forms require [version 2.1](compose-versioning.md#version-21) or above
### pids_limit
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Tunes a container's PIDs limit. Set to `-1` for unlimited PIDs.
```yaml
pids_limit: 10
```
### platform
> Added in [version 2.4](compose-versioning.md#version-24) file format.
Target platform containers for this service will run on, using the
`os[/arch[/variant]]` syntax, e.g.
```yaml
platform: osx
```
```yaml
platform: windows/amd64
```
```yaml
platform: linux/arm64/v8
```
This parameter determines which version of the image will be pulled and/or
on which platform the service's build will be performed.
### 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.
```yaml
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"
- "12400-12500:1240"
```
### runtime
> Added in [version 2.3](compose-versioning.md#version-23) file format.
Specify which runtime to use for the service's containers. Default runtime
and available runtimes are listed in the output of `docker info`.
```yaml
web:
image: busybox:latest
command: true
runtime: runc
```
### scale
> Added in [version 2.2](compose-versioning.md#version-22) file format.
Specify the default number of containers to deploy for this service. Whenever
you run `docker-compose up`, Compose creates or removes containers to match
the specified number. This value can be overridden using the
[`--scale`](../../engine/reference/commandline/compose_up.md)
```yaml
web:
image: busybox:latest
command: echo 'scaled'
scale: 3
```
### security_opt
Override the default labeling scheme for each container.
```yaml
security_opt:
- label:user:USER
- label:role:ROLE
```
### stop_grace_period
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`](#stop_signal)), before sending SIGKILL. Specified
as a [duration](#specifying-durations).
```yaml
stop_grace_period: 1s
```
```yaml
stop_grace_period: 1m30s
```
By default, `stop` waits 10 seconds for the container to exit before sending
SIGKILL.
### 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.
```yaml
stop_signal: SIGUSR1
```
### storage_opt
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Set storage driver options for this service.
```yaml
storage_opt:
size: '1G'
```
### sysctls
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Kernel parameters to set in the container. You can use either an array or a
dictionary.
```yaml
sysctls:
net.core.somaxconn: 1024
net.ipv4.tcp_syncookies: 0
```
```yaml
sysctls:
- net.core.somaxconn=1024
- net.ipv4.tcp_syncookies=0
```
### tmpfs
Mount a temporary file system inside the container. Can be a single value or a list.
```yaml
tmpfs: /run
```
```yaml
tmpfs:
- /run
- /tmp
```
### 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.
```yaml
ulimits:
nproc: 65535
nofile:
soft: 20000
hard: 40000
```
### userns_mode
> Added in [version 2.1](compose-versioning.md#version-21) file format.
```yaml
userns_mode: "host"
```
Disables the user namespace for this service, if Docker daemon is configured with user namespaces.
See [dockerd](../../engine/security/userns-remap.md#disable-namespace-remapping-for-a-container) for
more information.
### volumes
Mount host paths or named volumes. Named volumes need to be specified with the
[top-level `volumes` key](#volume-configuration-reference).
#### Short syntax
The short syntax uses the generic `[SOURCE:]TARGET[:MODE]` format, where
`SOURCE` can be either a host path or volume name. `TARGET` is the container
path where the volume is mounted. Standard modes are `ro` for read-only
and `rw` for read-write (default).
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 `..`.
```yaml
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
```
#### Long syntax
> Added in [version 2.3](compose-versioning.md#version-23) file format.
The long form syntax allows the configuration of additional fields that can't be
expressed in the short form.
- `type`: the mount type `volume`, `bind`, `tmpfs` or `npipe`
- `source`: the source of the mount, a path on the host for a bind mount, or the
name of a volume defined in the
[top-level `volumes` key](#volume-configuration-reference). Not applicable for a tmpfs mount.
- `target`: the path in the container where the volume is mounted
- `read_only`: flag to set the volume as read-only
- `bind`: configure additional bind options
- `propagation`: the propagation mode used for the bind
- `volume`: configure additional volume options
- `nocopy`: flag to disable copying of data from a container when a volume is
created
- `tmpfs`: configure additional tmpfs options
- `size`: the size for the tmpfs mount in bytes
```yaml
version: "{{ site.compose_file_v2 }}"
services:
web:
image: nginx:alpine
ports:
- "80:80"
volumes:
- type: volume
source: mydata
target: /data
volume:
nocopy: true
- type: bind
source: ./static
target: /opt/app/static
networks:
webnet:
volumes:
mydata:
```
> **Note**
>
> When creating bind mounts, using the long syntax requires the
> referenced folder to be created beforehand. Using the short syntax
> creates the folder on the fly if it doesn't exist.
> See the [bind mounts documentation](../../storage/bind-mounts.md#differences-between--v-and---mount-behavior)
> for more information.
### volume\_driver
Specify a default volume driver to be used for all declared volumes on this
service.
```yaml
volume_driver: mydriver
```
> **Note**
>
> In [version 2 files](compose-versioning.md#version-2), this
> option only applies 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](#volume-configuration-reference).
See [Docker Volumes](../../storage/volumes.md) and
[Volume Plugins](/engine/extend/plugins_volume/) 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.
```yaml
volumes_from:
- service_name
- service_name:ro
- container:container_name
- container:container_name:rw
```
> Changed in [version 2](compose-versioning.md#version-2) file format.
### restart
`no` is the default restart policy, and it doesn't restart a container under any circumstance. When `always` is specified, the container always restarts. The `on-failure` policy restarts a container if the exit code indicates an on-failure error.
```yaml
restart: "no"
```
```yaml
restart: "always"
```
```yaml
restart: "on-failure"
```
```yaml
restart: "unless-stopped"
```
{: id="cpu-and-other-resources"}
### cpu_count, cpu_percent, cpu\_shares, cpu\_period, cpu\_quota, cpus, cpuset, domainname, hostname, ipc, mac\_address, mem\_limit, memswap\_limit, mem\_swappiness, mem\_reservation, oom_kill_disable, oom_score_adj, privileged, read\_only, shm\_size, stdin\_open, tty, user, working\_dir
Each of these is a single value, analogous to its
[docker run](../../engine/reference/run.md#runtime-constraints-on-resources) counterpart.
> Added in [version 2.2](compose-versioning.md#version-22) file format.
>
> The `cpu_count`, `cpu_percent`, and `cpus` options were added in [version 2.2](compose-versioning.md#version-22).
> Added in [version 2.1](compose-versioning.md#version-21) file format.
>
> The `oom_kill_disable` and `cpu_period` options were added in [version 2.1](compose-versioning.md#version-21).
```yaml
cpu_count: 2
cpu_percent: 50
cpus: 0.5
cpu_shares: 73
cpu_quota: 50000
cpu_period: 20ms
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
mem_reservation: 512m
privileged: true
oom_score_adj: 500
oom_kill_disable: true
read_only: true
shm_size: 64M
stdin_open: true
tty: true
```
<a name="orig-resources"></a>
## Specifying durations
Some configuration options, such as the `interval` and `timeout` sub-options for
[`healthcheck`](#healthcheck), accept a duration as a string in a
format that looks like this:
2.5s
10s
1m30s
2h32m
5h34m56s
The supported units are `us`, `ms`, `s`, `m` and `h`.
## Specifying byte values
Some configuration options, such as the `device_read_bps` sub-option for
[`blkio_config`](#blkio_config), accept a byte value as a string in a format
that looks like this:
2b
1024kb
2048k
300m
1gb
The supported units are `b`, `k`, `m` and `g`, and their alternative notation `kb`,
`mb` and `gb`. Decimal values are not supported at this time.
## Volume configuration reference
While it is possible to declare [volumes](#volumes) on the fly as part of the
service declaration, this section allows you to create named volumes that can be
reused across multiple services (without relying on `volumes_from`), and are
easily retrieved and inspected using the docker command line or API.
See the [docker volume](../../engine/reference/commandline/volume_create.md)
subcommand documentation for more information.
See [use volumes](../../storage/volumes.md) and [volume plugins](/engine/extend/plugins_volume/)
for general information on volumes.
Here's an example of a two-service setup where a database's data directory is
shared with another service as a volume so that it can be periodically backed
up:
```yaml
version: "{{ site.compose_file_v2 }}"
services:
db:
image: db
volumes:
- data-volume:/var/lib/db
backup:
image: backup-service
volumes:
- data-volume:/var/lib/backup/data
volumes:
data-volume:
```
An entry under the top-level `volumes` key can be empty, in which case it
uses the default driver configured by the Engine (in most cases, this is the
`local` driver). Optionally, you can configure it with the following keys:
### driver
Specify which volume driver should be used for this volume. Defaults to whatever
driver the Docker Engine has been configured to use, which in most cases is
`local`. If the driver is not available, the Engine returns an error when
`docker-compose up` tries to create the volume.
```yaml
driver: foobar
```
### driver_opts
Specify a list of options as key-value pairs to pass to the driver for this
volume. Those options are driver-dependent - consult the driver's
documentation for more information. Optional.
```yaml
volumes:
example:
driver_opts:
type: "nfs"
o: "addr=10.40.0.199,nolock,soft,rw"
device: ":/docker/example"
```
### external
If set to `true`, specifies that this volume has been created outside of
Compose. `docker-compose up` does not attempt to create it, and raises
an error if it doesn't exist.
For version 2.0 of the format, `external` cannot be used in
conjunction with other volume configuration keys (`driver`, `driver_opts`,
`labels`). This limitation no longer exists for
[version 2.1](compose-versioning.md#version-21) and above.
In the example below, instead of attempting to create a volume called
`[projectname]_data`, Compose looks for an existing volume simply
called `data` and mount it into the `db` service's containers.
```yaml
version: "{{ site.compose_file_v2 }}"
services:
db:
image: postgres
volumes:
- data:/var/lib/postgresql/data
volumes:
data:
external: true
```
You can also specify the name of the volume separately from the name used to
refer to it within the Compose file:
```yaml
volumes:
data:
external:
name: actual-name-of-volume
```
> Deprecated in [version 2.1](compose-versioning.md#version-21) file format.
>
> external.name was deprecated in version 2.1 file format use `name` instead.
{: .important }
### labels
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Add metadata to containers using
[Docker labels](../../config/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.
```yaml
labels:
com.example.description: "Database volume"
com.example.department: "IT/Ops"
com.example.label-with-empty-value: ""
```
```yaml
labels:
- "com.example.description=Database volume"
- "com.example.department=IT/Ops"
- "com.example.label-with-empty-value"
```
### name
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Set a custom name for this volume. The name field can be used to reference
volumes that contain special characters. The name is used as is
and will **not** be scoped with the stack name.
```yaml
version: "{{ site.compose_file_v2 }}"
volumes:
data:
name: my-app-data
```
It can also be used in conjunction with the `external` property:
```yaml
version: "{{ site.compose_file_v2 }}"
volumes:
data:
external: true
name: my-app-data
```
## Network configuration reference
The top-level `networks` key lets you specify networks to be created. For a full
explanation of Compose's use of Docker networking features, see the
[Networking guide](../networking.md).
### driver
Specify which driver should be used for this network.
The default driver depends on how the Docker Engine you're using is configured,
but in most instances it is `bridge` on a single host and `overlay` on a
Swarm.
The Docker Engine returns an error if the driver is not available.
```yaml
driver: overlay
```
> Changed in [version 2.1](compose-versioning.md#version-21) file format.
>
> Starting with Compose file format 2.1, overlay networks are always created as
> `attachable`, and this is not configurable. This means that standalone
> containers can connect to overlay networks.
### driver_opts
Specify a list of options as key-value pairs to pass to the driver for this
network. Those options are driver-dependent - consult the driver's
documentation for more information. Optional.
```yaml
driver_opts:
foo: "bar"
baz: 1
```
### enable_ipv6
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Enable IPv6 networking on this network.
### ipam
Specify custom IPAM config. This is an object with several properties, each of
which is optional:
- `driver`: Custom IPAM driver, instead of the default.
- `config`: A list with zero or more config blocks, each containing any of
the following keys:
- `subnet`: Subnet in CIDR format that represents a network segment
- `ip_range`: Range of IPs from which to allocate container IPs
- `gateway`: IPv4 or IPv6 gateway for the master subnet
- `aux_addresses`: Auxiliary IPv4 or IPv6 addresses used by Network driver,
as a mapping from hostname to IP
- `options`: Driver-specific options as a key-value mapping.
A full example:
```yaml
ipam:
driver: default
config:
- subnet: 172.28.0.0/16
ip_range: 172.28.5.0/24
gateway: 172.28.5.254
aux_addresses:
host1: 172.28.1.5
host2: 172.28.1.6
host3: 172.28.1.7
options:
foo: bar
baz: "0"
```
### internal
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](compose-versioning.md#version-21) file format.
Add metadata to containers using
[Docker labels](../../config/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.
```yaml
labels:
com.example.description: "Financial transaction network"
com.example.department: "Finance"
com.example.label-with-empty-value: ""
```
```yaml
labels:
- "com.example.description=Financial transaction network"
- "com.example.department=Finance"
- "com.example.label-with-empty-value"
```
### external
If set to `true`, specifies that this network has been created outside of
Compose. `docker-compose up` does not attempt to create it, and raises
an error if it doesn't exist.
For version 2.0 of the format, `external` cannot be used in conjunction with
other network configuration keys (`driver`, `driver_opts`, `ipam`, `internal`).
This limitation no longer exists for
[version 2.1](compose-versioning.md#version-21) and above.
In the example below, `proxy` is the gateway to the outside world. Instead of
attempting to create a network called `[projectname]_outside`, Compose
looks for an existing network simply called `outside` and connect the `proxy`
service's containers to it.
```yaml
version: "{{ site.compose_file_v2 }}"
services:
proxy:
build: ./proxy
networks:
- outside
- default
app:
build: ./app
networks:
- default
networks:
outside:
external: true
```
You can also specify the name of the network separately from the name used to
refer to it within the Compose file:
```yaml
version: "{{ site.compose_file_v2 }}"
networks:
outside:
external:
name: actual-name-of-network
```
Not supported for version 2 `docker-compose` files. Use
[network_mode](#network_mode) instead.
### name
> Added in [version 2.1](compose-versioning.md#version-21) file format.
Set a custom name for this network. The name field can be used to reference
networks which contain special characters. The name is used as is
and will **not** be scoped with the stack name.
```yaml
version: "{{ site.compose_file_v2 }}"
networks:
network1:
name: my-app-net
```
It can also be used in conjunction with the `external` property:
```yaml
version: "{{ site.compose_file_v2 }}"
networks:
network1:
external: true
name: my-app-net
```
## Variable substitution
{% include content/compose-var-sub.md %}
## Extension fields
> Added in [version 2.1](compose-versioning.md#version-21) file format.
{% include content/compose-extfields-sub.md %}
## Compose documentation
- [User guide](../index.md)
- [Installing Compose](../install/index.md)
- [Compose file versions and upgrading](compose-versioning.md)
- [Sample apps with Compose](../samples-for-compose.md)
- [Command line reference](../reference/index.md)
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