Services top-level elements
A service is an abstract definition of a computing resource within an application which can be scaled or replaced independently from other components. Services are backed by a set of containers, run by the platform according to replication requirements and placement constraints. As services are backed by containers, they are defined by a Docker image and set of runtime arguments. All containers within a service are identically created with these arguments.
A Compose file must declare a services
top-level element as a map whose keys are string representations of service names,
and whose values are service definitions. A service definition contains the configuration that is applied to each
service container.
Each service may also include a build
section, which defines how to create the Docker image for the service.
Compose supports building docker images using this service definition. If not used, the build
section is ignored and the Compose file is still considered valid. Build support is an optional aspect of the Compose Specification, and is
described in detail in the
Compose Build Specification documentation.
Each service defines runtime constraints and requirements to run its containers. The deploy
section groups
these constraints and allows the platform to adjust the deployment strategy to best match containers' needs with
available resources. Deploy support is an optional aspect of the Compose Specification, and is
described in detail in the
Compose Deploy Specification documentation.
If not implemented the deploy
section is ignored and the Compose file is still considered valid.
Examples
Simple example
The following example demonstrates how to define two simple services, set their images, map ports, and configure basic environment variables using Docker Compose.
services:
web:
image: nginx:latest
ports:
- "8080:80"
db:
image: postgres:13
environment:
POSTGRES_USER: example
POSTGRES_DB: exampledb
Advanced example
In the following example, the proxy
service uses the Nginx image, mounts a local Nginx configuration file into the container, exposes port 80
and depends on the backend
service.
The backend
service builds an image from the Dockerfile located in the backend
directory that is set to build at stage builder
.
services:
proxy:
image: nginx
volumes:
- type: bind
source: ./proxy/nginx.conf
target: /etc/nginx/conf.d/default.conf
read_only: true
ports:
- 80:80
depends_on:
- backend
backend:
build:
context: backend
target: builder
For more example Compose files, explore the Awesome Compose samples.
Attributes
annotations
annotations
defines annotations for the container. annotations
can use either an array or a map.
annotations:
com.example.foo: bar
annotations:
- com.example.foo=bar
attach
When attach
is defined and set to false
Compose does not collect service logs,
until you explicitly request it to.
The default service configuration is attach: true
.
build
build
specifies the build configuration for creating a container image from source, as defined in the
Compose Build Specification.
blkio_config
blkio_config
defines a set of configuration options to set block IO limits for a service.
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
: Defines 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.
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
: Defines 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 a 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
: Defines the symbolic path to the affected device.weight
: An integer value between 10 and 1000.
cpu_count
cpu_count
defines the number of usable CPUs for service container.
cpu_percent
cpu_percent
defines the usable percentage of the available CPUs.
cpu_shares
cpu_shares
defines, as integer value, a service container's relative CPU weight versus other containers.
cpu_period
cpu_period
configures CPU CFS (Completely Fair Scheduler) period when a platform is based
on Linux kernel.
cpu_quota
cpu_quota
configures CPU CFS (Completely Fair Scheduler) quota when a platform is based
on Linux kernel.
cpu_rt_runtime
cpu_rt_runtime
configures CPU allocation parameters for platforms with support for realtime scheduler. It can be either
an integer value using microseconds as unit or a
duration.
cpu_rt_runtime: '400ms'
cpu_rt_runtime: 95000`
cpu_rt_period
cpu_rt_period
configures CPU allocation parameters for platforms with support for realtime scheduler. It can be either
an integer value using microseconds as unit or a
duration.
cpu_rt_period: '1400us'
cpu_rt_period: 11000`
cpus
cpus
define the number of (potentially virtual) CPUs to allocate to service containers. This is a fractional number.
0.000
means no limit.
When set, cpus
must be consistent with the cpus
attribute in the
Deploy Specification.
cpuset
cpuset
defines the explicit CPUs in which to allow execution. Can be a range 0-3
or a list 0,1
cap_add
cap_add
specifies additional container
capabilities
as strings.
cap_add:
- ALL
cap_drop
cap_drop
specifies container
capabilities to drop
as strings.
cap_drop:
- NET_ADMIN
- SYS_ADMIN
cgroup
cgroup
specifies the cgroup namespace to join. When unset, it is the container runtime's decision to
select which cgroup namespace to use, if supported.
host
: Runs the container in the Container runtime cgroup namespace.private
: Runs the container in its own private cgroup namespace.
cgroup_parent
cgroup_parent
specifies an optional parent
cgroup for the container.
cgroup_parent: m-executor-abcd
command
command
overrides the default command declared by the container image, for example by Dockerfile's CMD
.
command: bundle exec thin -p 3000
The value can also be a list, in a manner similar to Dockerfile:
command: [ "bundle", "exec", "thin", "-p", "3000" ]
If the value is null
, the default command from the image is used.
If the value is []
(empty list) or ''
(empty string), the default command declared by the image is ignored,
i.e. overridden to be empty.
configs
Configs allow services to adapt their behaviour without the need to rebuild a Docker image.
Services can only access configs when explicitly granted by the configs
attribute. Two different syntax variants are supported.
Compose reports an error if config
doesn't exist on the platform or isn't defined in the
configs
top-level element in the Compose file.
There are two syntaxes defined for configs: a short syntax and a long syntax.
You can grant a service access to multiple configs, and you can mix long and short syntax.
Short syntax
The short syntax variant only specifies the config name. This grants the
container access to the config and mounts it as files into a service’s container’s filesystem. The location of the mount point within the container defaults to /<config_name>
in Linux containers, and C:\<config-name>
in Windows containers.
The following example uses the short syntax to grant the redis
service
access to the my_config
and my_other_config
configs. The value of
my_config
is set to the contents of the file ./my_config.txt
, and
my_other_config
is defined as an external resource, which means that it has
already been defined in the platform. If the external config does not exist,
the deployment fails.
services:
redis:
image: redis:latest
configs:
- my_config
- my_other_config
configs:
my_config:
file: ./my_config.txt
my_other_config:
external: true
Long syntax
The long syntax provides more granularity in how the config is created within the service's task containers.
source
: The name of the config as it exists in the platform.target
: The path and name of the file to be mounted in the service's task containers. Defaults to/<source>
if not specified.uid
andgid
: The numeric UID or GID that owns the mounted config file within the service's task containers. Default value when not specified is USER running container.mode
: The permissions for the file that is mounted within the service's task containers, in octal notation. Default value is world-readable (0444
). Writable bit must be ignored. The executable bit can be set.
The following example sets the name of my_config
to redis_config
within the
container, sets the mode to 0440
(group-readable) and sets the user and group
to 103
. The redis
service does not have access to the my_other_config
config.
services:
redis:
image: redis:latest
configs:
- source: my_config
target: /redis_config
uid: "103"
gid: "103"
mode: 0440
configs:
my_config:
external: true
my_other_config:
external: true
container_name
container_name
is a string that specifies a custom container name, rather than a name generated by default.
container_name: my-web-container
Compose does not scale a service beyond one container if the Compose file specifies a
container_name
. Attempting to do so results in an error.
container_name
follows the regex format of [a-zA-Z0-9][a-zA-Z0-9_.-]+
credential_spec
credential_spec
configures the credential spec for a managed service account.
If you have services that use Windows containers, you can use file:
and
registry:
protocols for credential_spec
. Compose also supports additional
protocols for custom use-cases.
The credential_spec
must be in the format file://<filename>
or registry://<value-name>
.
credential_spec:
file: my-credential-spec.json
When using registry:
, the credential spec is read from the Windows registry on
the daemon's host. A registry value with the given name must be located in:
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\Containers\CredentialSpecs
The following example loads the credential spec from a value named my-credential-spec
in the registry:
credential_spec:
registry: my-credential-spec
Example gMSA configuration
When configuring a gMSA credential spec for a service, you only need
to specify a credential spec with config
, as shown in the following example:
services:
myservice:
image: myimage:latest
credential_spec:
config: my_credential_spec
configs:
my_credentials_spec:
file: ./my-credential-spec.json|
depends_on
With the depends_on
attribute, you can control the order of service startup and shutdown. It is useful if services are closely coupled, and the startup sequence impacts the application's functionality.
Short syntax
The short syntax variant only specifies service names of the dependencies. Service dependencies cause the following behaviors:
Compose creates services in dependency order. In the following example,
db
andredis
are created beforeweb
.Compose removes services in dependency order. In the following example,
web
is removed beforedb
andredis
.
Simple example:
services:
web:
build: .
depends_on:
- db
- redis
redis:
image: redis
db:
image: postgres
Compose guarantees dependency services have been started before starting a dependent service. Compose waits for dependency services to be "ready" before starting a dependent service.
Long syntax
The long form syntax enables the configuration of additional fields that can't be expressed in the short form.
restart
: When set totrue
Compose restarts this service after it updates the dependency service. This applies to an explicit restart controlled by a Compose operation, and excludes automated restart by the container runtime after the container dies. Introduced in Docker Compose version 2.17.0.condition
: Sets the condition under which dependency is considered satisfiedservice_started
: An equivalent of the short syntax described aboveservice_healthy
: Specifies that a dependency is expected to be "healthy" (as indicated by healthcheck) before starting a dependent service.service_completed_successfully
: Specifies that a dependency is expected to run to successful completion before starting a dependent service.
required
: When set tofalse
Compose only warns you when the dependency service isn't started or available. If it's not defined the default value ofrequired
istrue
. Introduced in Docker Compose version 2.20.0.
Service dependencies cause the following behaviors:
Compose creates services in dependency order. In the following example,
db
andredis
are created beforeweb
.Compose waits for healthchecks to pass on dependencies marked with
service_healthy
. In the following example,db
is expected to be "healthy" beforeweb
is created.Compose removes services in dependency order. In the following example,
web
is removed beforedb
andredis
.
services:
web:
build: .
depends_on:
db:
condition: service_healthy
restart: true
redis:
condition: service_started
redis:
image: redis
db:
image: postgres
Compose guarantees dependency services are started before
starting a dependent service.
Compose guarantees dependency services marked with
service_healthy
are "healthy" before starting a dependent service.
deploy
deploy
specifies the configuration for the deployment and lifecycle of services, as defined
in the Compose Deploy Specification.
develop
develop
specifies the development configuration for maintaining a container in sync with source, as defined in the
Development Section.
device_cgroup_rules
device_cgroup_rules
defines a list of device cgroup rules for this container.
The format is the same format the Linux kernel specifies in the
Control Groups
Device Whitelist Controller.
device_cgroup_rules:
- 'c 1:3 mr'
- 'a 7:* rmw'
devices
devices
defines a list of device mappings for created containers in the form of
HOST_PATH:CONTAINER_PATH[:CGROUP_PERMISSIONS]
.
devices:
- "/dev/ttyUSB0:/dev/ttyUSB0"
- "/dev/sda:/dev/xvda:rwm"
dns
dns
defines custom DNS servers to set on the container network interface configuration. It can be a single value or a list.
dns: 8.8.8.8
dns:
- 8.8.8.8
- 9.9.9.9
dns_opt
dns_opt
list custom DNS options to be passed to the container’s DNS resolver (/etc/resolv.conf
file on Linux).
dns_opt:
- use-vc
- no-tld-query
dns_search
dns_search
defines custom DNS search domains to set on container network interface configuration. It can be a single value or a list.
dns_search: example.com
dns_search:
- dc1.example.com
- dc2.example.com
domainname
domainname
declares a custom domain name to use for the service container. It must be a valid RFC 1123 hostname.
driver_opts
driver_opts
specifies a list of options as key-value pairs to pass to the driver. These options are
driver-dependent.
services:
app:
networks:
app_net:
driver_opts:
com.docker.network.bridge.host_binding_ipv4: "127.0.0.1"
Consult the network drivers documentation for more information.
entrypoint
entrypoint
declares the default entrypoint for the service container.
This overrides the ENTRYPOINT
instruction from the service's Dockerfile.
If entrypoint
is non-null, Compose ignores any default command from the image, for example the CMD
instruction in the Dockerfile.
See also
command
to set or override the default command to be executed by the entrypoint process.
In its short form, the value can be defined as a string:
entrypoint: /code/entrypoint.sh
Alternatively, the value can also be a list, in a manner similar to the Dockerfile:
entrypoint:
- php
- -d
- zend_extension=/usr/local/lib/php/extensions/no-debug-non-zts-20100525/xdebug.so
- -d
- memory_limit=-1
- vendor/bin/phpunit
If the value is null
, the default entrypoint from the image is used.
If the value is []
(empty list) or ''
(empty string), the default entrypoint declared by the image is ignored,
i.e. overridden to be empty.
env_file
The env_file
attribute is used to specify one or more files that contain environment variables to be passed to the containers.
env_file: .env
env_file
can also be a list. The files in the list are processed from the top down. For the same variable
specified in two env files, the value from the last file in the list stands.
env_file:
- ./a.env
- ./b.env
List elements can also be declared as a mapping, which then lets you set an additional
attribute required
. This defaults to true
. When required
is set to false
and the .env
file is missing,
Compose silently ignores the entry.
env_file:
- path: ./default.env
required: true # default
- path: ./override.env
required: false
required
attribute is available with Docker Compose version 2.24.0 or later.
Relative path are resolved from the Compose file's parent folder. As absolute paths prevent the Compose
file from being portable, Compose warns you when such a path is used to set env_file
.
Environment variables declared in the environment section override these values. This holds true even if those values are empty or undefined.
Env_file format
Each line in an .env
file must be in VAR[=[VAL]]
format. The following syntax rules apply:
- Lines beginning with
#
are processed as comments and ignored. - Blank lines are ignored.
- Unquoted and double-quoted (
"
) values have Interpolation applied. - Each line represents a key-value pair. Values can optionally be quoted.
VAR=VAL
->VAL
VAR="VAL"
->VAL
VAR='VAL'
->VAL
- Inline comments for unquoted values must be preceded with a space.
VAR=VAL # comment
->VAL
VAR=VAL# not a comment
->VAL# not a comment
- Inline comments for quoted values must follow the closing quote.
VAR="VAL # not a comment"
->VAL # not a comment
VAR="VAL" # comment
->VAL
- Single-quoted (
'
) values are used literally.VAR='$OTHER'
->$OTHER
VAR='${OTHER}'
->${OTHER}
- Quotes can be escaped with
\
.VAR='Let\'s go!'
->Let's go!
VAR="{\"hello\": \"json\"}"
->{"hello": "json"}
- Common shell escape sequences including
\n
,\r
,\t
, and\\
are supported in double-quoted values.VAR="some\tvalue"
->some value
VAR='some\tvalue'
->some\tvalue
VAR=some\tvalue
->some\tvalue
VAL
may be omitted, in such cases the variable value is an empty string.
=VAL
may be omitted, in such cases the variable is unset.
# Set Rails/Rack environment
RACK_ENV=development
VAR="quoted"
environment
The environment
attribute defines environment variables set in the container. environment
can use either an array or a
map. Any boolean values; true, false, yes, no, should be enclosed in quotes to ensure
they are not converted to True or False by the YAML parser.
Environment variables can be declared by a single key (no value to equals sign). In this case Compose relies on you to resolve the value. If the value is not resolved, the variable is unset and is removed from the service container environment.
Map syntax:
environment:
RACK_ENV: development
SHOW: "true"
USER_INPUT:
Array syntax:
environment:
- RACK_ENV=development
- SHOW=true
- USER_INPUT
When both env_file
and environment
are set for a service, values set by environment
have precedence.
expose
expose
defines the (incoming) port or a range of ports that Compose exposes from the container. These ports must be
accessible to linked services and should not be published to the host machine. Only the internal container
ports can be specified.
Syntax is <portnum>/[<proto>]
or <startport-endport>/[<proto>]
for a port range.
When not explicitly set, tcp
protocol is used.
expose:
- "3000"
- "8000"
- "8080-8085/tcp"
Note
If the Dockerfile for the image already exposes ports, it is visible to other containers on the network even if
expose
is not set in your Compose file.
extends
extends
lets you share common configurations among different files, or even different projects entirely. With extends
you can define a common set of service options in one place and refer to it from anywhere. You can refer to another Compose file and select a service you want to also use in your own application, with the ability to override some attributes for your own needs.
You can use extends
on any service together with other configuration keys. The extends
value must be a mapping
defined with a required service
and an optional file
key.
extends:
file: common.yml
service: webapp
service
: Defines the name of the service being referenced as a base, for exampleweb
ordatabase
.file
: The location of a Compose configuration file defining that service.
When a service uses extends
, it can also specify dependencies on other resources, an explicit volumes
declaration for instance. However, it's important to note that extends
does not automatically incorporate the target volume definition into the extending Compose file. Instead, you are responsible for ensuring that an equivalent resource exists for the service being extended to maintain consistency. Docker Compose verifies that a resource with the referenced ID is present within the Compose model.
Dependencies on other resources in an extends
target can be:
- An explicit reference by
volumes
,networks
,configs
,secrets
,links
,volumes_from
ordepends_on
- A reference to another service using the
service:{name}
syntax in namespace declaration (ipc
,pid
,network_mode
)
Circular references with extends
are not supported, Compose returns an error when one is detected.
Finding referenced service
file
value can be:
- Not present. This indicates that another service within the same Compose file is being referenced.
- File path, which can be either:
- Relative path. This path is considered as relative to the location of the main Compose file.
- Absolute path.
A service denoted by service
must be present in the identified referenced Compose file.
Compose returns an error if:
- The service denoted by
service
is not found. - The Compose file denoted by
file
is not found.
Merging service definitions
Two service definitions, the main one in the current Compose file and the referenced one
specified by extends
, are merged in the following way:
- Mappings: Keys in mappings of the main service definition override keys in mappings of the referenced service definition. Keys that aren't overridden are included as is.
- Sequences: Items are combined together into a new sequence. The order of elements is preserved with the referenced items coming first and main items after.
- Scalars: Keys in the main service definition take precedence over keys in the referenced one.
Mappings
The following keys should be treated as mappings: annotations
, build.args
, build.labels
,
build.extra_hosts
, deploy.labels
, deploy.update_config
, deploy.rollback_config
,
deploy.restart_policy
, deploy.resources.limits
, environment
, healthcheck
,
labels
, logging.options
, sysctls
, storage_opt
, extra_hosts
, ulimits
.
One exception that applies to healthcheck
is that the main mapping cannot specify
disable: true
unless the referenced mapping also specifies disable: true
. Compose returns an error in this case.
For example, the input below:
services:
common:
image: busybox
environment:
TZ: utc
PORT: 80
cli:
extends:
service: common
environment:
PORT: 8080
Produces the following configuration for the cli
service. The same output is
produced if array syntax is used.
environment:
PORT: 8080
TZ: utc
image: busybox
Items under blkio_config.device_read_bps
, blkio_config.device_read_iops
,
blkio_config.device_write_bps
, blkio_config.device_write_iops
, devices
and
volumes
are also treated as mappings where key is the target path inside the
container.
For example, the input below:
services:
common:
image: busybox
volumes:
- common-volume:/var/lib/backup/data:rw
cli:
extends:
service: common
volumes:
- cli-volume:/var/lib/backup/data:ro
Produces the following configuration for the cli
service. Note that the mounted path
now points to the new volume name and ro
flag was applied.
image: busybox
volumes:
- cli-volume:/var/lib/backup/data:ro
If the referenced service definition contains extends
mapping, the items under it
are simply copied into the new merged definition. The merging process is then kicked
off again until no extends
keys are remaining.
For example, the input below:
services:
base:
image: busybox
user: root
common:
image: busybox
extends:
service: base
cli:
extends:
service: common
Produces the following configuration for the cli
service. Here, cli
services
gets user
key from common
service, which in turn gets this key from base
service.
image: busybox
user: root
Sequences
The following keys should be treated as sequences: cap_add
, cap_drop
, configs
,
deploy.placement.constraints
, deploy.placement.preferences
,
deploy.reservations.generic_resources
, device_cgroup_rules
, expose
,
external_links
, ports
, secrets
, security_opt
.
Any duplicates resulting from the merge are removed so that the sequence only
contains unique elements.
For example, the input below:
services:
common:
image: busybox
security_opt:
- label:role:ROLE
cli:
extends:
service: common
security_opt:
- label:user:USER
Produces the following configuration for the cli
service.
image: busybox
security_opt:
- label:role:ROLE
- label:user:USER
In case list syntax is used, the following keys should also be treated as sequences:
dns
, dns_search
, env_file
, tmpfs
. Unlike sequence fields mentioned above,
duplicates resulting from the merge are not removed.
Scalars
Any other allowed keys in the service definition should be treated as scalars.
external_links
external_links
link service containers to services managed outside of your Compose application.
external_links
define the name of an existing service to retrieve using the platform lookup mechanism.
An alias of the form SERVICE:ALIAS
can be specified.
external_links:
- redis
- database:mysql
- database:postgresql
extra_hosts
extra_hosts
adds hostname mappings to the container network interface configuration (/etc/hosts
for Linux).
Short syntax
Short syntax uses plain strings in a list. Values must set hostname and IP address for additional hosts in the form of HOSTNAME=IP
.
extra_hosts:
- "somehost=162.242.195.82"
- "otherhost=50.31.209.229"
- "myhostv6=::1"
IPv6 addresses can be enclosed in square brackets, for example:
extra_hosts:
- "myhostv6=[::1]"
The separator =
is preferred, but :
can also be used. Introduced in Docker Compose version
2.24.1. For example:
extra_hosts:
- "somehost:162.242.195.82"
- "myhostv6:::1"
Long syntax
Alternatively, extra_hosts
can be set as a mapping between hostname(s) and IP(s)
extra_hosts:
somehost: "162.242.195.82"
otherhost: "50.31.209.229"
myhostv6: "::1"
Compose creates a matching entry with the IP address and hostname in the container's network
configuration, which means for Linux /etc/hosts
get extra lines:
162.242.195.82 somehost
50.31.209.229 otherhost
::1 myhostv6
group_add
group_add
specifies additional groups, by name or number, which the user inside the container must be a member of.
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 a shared volume. That file can be owned by a group shared by all the containers, and specified in
group_add
.
services:
myservice:
image: alpine
group_add:
- mail
Running id
inside the created container must show that the user belongs to the mail
group, which would not have
been the case if group_add
were not declared.
healthcheck
The healthcheck
attribute declares a check that's run to determine whether or not the service containers are "healthy". It works in the same way, and has the same default values, as the HEALTHCHECK Dockerfile instruction
set by the service's Docker image. Your Compose file can override the values set in the Dockerfile.
For more information on HEALTHCHECK
, see the
Dockerfile reference.
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost"]
interval: 1m30s
timeout: 10s
retries: 3
start_period: 40s
start_interval: 5s
interval
, timeout
, start_period
, and start_interval
are
specified as durations. Introduced in Docker Compose version
2.20.2
test
defines the command Compose runs to check container health. It can 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.
# Hit the local web app
test: ["CMD", "curl", "-f", "http://localhost"]
Using CMD-SHELL
runs the command configured as a string using the container's default shell
(/bin/sh
for Linux). Both forms below are equivalent:
test: ["CMD-SHELL", "curl -f http://localhost || exit 1"]
test: curl -f https://localhost || exit 1
NONE
disables the healthcheck, and is mostly useful to disable the Healthcheck Dockerfile instruction set by the service's Docker image. Alternatively,
the healthcheck set by the image can be disabled by setting disable: true
:
healthcheck:
disable: true
hostname
hostname
declares a custom host name to use for the service container. It must be a valid RFC 1123 hostname.
image
image
specifies the image to start the container from. image
must follow the Open Container Specification
addressable image format,
as [<registry>/][<project>/]<image>[:<tag>|@<digest>]
.
image: redis
image: redis:5
image: redis@sha256:0ed5d5928d4737458944eb604cc8509e245c3e19d02ad83935398bc4b991aac7
image: library/redis
image: docker.io/library/redis
image: my_private.registry:5000/redis
If the image does not exist on the platform, Compose attempts to pull it based on the pull_policy
.
If you are also using the
Compose Build Specification, there are alternative options for controlling the precedence of
pull over building the image from source, however pulling the image is the default behavior.
image
may be omitted from a Compose file as long as a build
section is declared. If you are not using the Compose Build Specification, Compose won't work if image
is missing from the Compose file.
init
init
runs an init process (PID 1) inside the container that forwards signals and reaps processes.
Set this option to true
to enable this feature for the service.
services:
web:
image: alpine:latest
init: true
The init binary that is used is platform specific.
ipc
ipc
configures the IPC isolation mode set by the service container.
shareable
: Gives the container its own private IPC namespace, with a possibility to share it with other containers.service:{name}
: Makes the container join another container's (shareable
) IPC namespace.
ipc: "shareable"
ipc: "service:[service name]"
isolation
isolation
specifies a container’s isolation technology. Supported values are platform specific.
labels
labels
add metadata to containers. You can use either an array or a map.
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"
Compose creates containers with canonical labels:
com.docker.compose.project
set on all resources created by Compose to the user project namecom.docker.compose.service
set on service containers with service name as defined in the Compose file
The com.docker.compose
label prefix is reserved. Specifying labels with this prefix in the Compose file
results in a runtime error.
links
links
defines a network 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 are reachable at a hostname identical to the alias, or the service name if no alias is specified.
Links are not required to enable services to communicate. When no specific network configuration is set,
any service is able to reach any other service at that service’s name on the default
network. If services
do declare networks they are attached to, links
does not override the network configuration and services not
attached to a shared network are not be able to communicate. Compose doesn't warn you about a configuration mismatch.
Links also express implicit dependency between services in the same way as depends_on, so they determine the order of service startup.
logging
logging
defines the logging configuration for the service.
logging:
driver: syslog
options:
syslog-address: "tcp://192.168.0.42:123"
The driver
name specifies a logging driver for the service's containers. The default and available values
are platform specific. Driver specific options can be set with options
as key-value pairs.
mac_address
Available with Docker Compose version 2.24.0 and later.
mac_address
sets a MAC address for the service container.
Note
Container runtimes might reject this value (ie. Docker Engine >= v25.0). In that case, you should use networks.mac_address instead.
mem_limit
mem_limit
configures a limit on the amount of memory a container can allocate, set as a string expressing a
byte value.
When set, mem_limit
must be consistent with the limits.memory
attribute in the
Deploy Specification.
mem_reservation
mem_reservation
configures a reservation on the amount of memory a container can allocate, set as a string expressing a
byte value.
When set, mem_reservation
must be consistent with the reservations.memory
attribute in the
Deploy Specification.
mem_swappiness
mem_swappiness
defines as a percentage, a value between 0 and 100, for the host kernel to swap out
anonymous memory pages used by a container.
0
: Turns off anonymous page swapping.100
: Sets all anonymous pages as swappable.
The default value is platform specific.
memswap_limit
memswap_limit
defines the amount of memory the container is allowed to swap to disk. This is a modifier
attribute that only has meaning if
memory
is also set. Using swap lets the container write excess
memory requirements to disk when the container has exhausted all the memory that is available to it.
There is a performance penalty for applications that swap memory to disk often.
- If
memswap_limit
is set to a positive integer, then bothmemory
andmemswap_limit
must be set.memswap_limit
represents the total amount of memory and swap that can be used, andmemory
controls the amount used by non-swap memory. So ifmemory
="300m" andmemswap_limit
="1g", the container can use 300m of memory and 700m (1g - 300m) swap. - If
memswap_limit
is set to 0, the setting is ignored, and the value is treated as unset. - If
memswap_limit
is set to the same value asmemory
, andmemory
is set to a positive integer, the container does not have access to swap. - If
memswap_limit
is unset, andmemory
is set, the container can use as much swap as thememory
setting, if the host container has swap memory configured. For instance, ifmemory
="300m" andmemswap_limit
is not set, the container can use 600m in total of memory and swap. - If
memswap_limit
is explicitly set to -1, the container is allowed to use unlimited swap, up to the amount available on the host system.
network_mode
network_mode
sets a service container's network mode.
none
: Turns off all container networking.host
: Gives the container raw access to the host's network interface.service:{name}
: Gives the container access to the specified container by referring to its service name.container:{name}
: Gives the container access to the specified container by referring to its container ID.
For more information container networks, see the Docker Engine documentation.
network_mode: "host"
network_mode: "none"
network_mode: "service:[service name]"
When set, the
networks
attribute is not allowed and Compose rejects any
Compose file containing both attributes.
networks
The networks
attribute defines the networks that service containers are attached to, referencing entries under the
networks
top-level element. The networks
attribute helps manage the networking aspects of containers, providing control over how services are segmented and interact within the Docker environment. This is used to specify which networks the containers for that service should connect to. This is important for defining how containers communicate with each other and externally.
services:
some-service:
networks:
- some-network
- other-network
For more information about the networks
top-level element, see
Networks.
aliases
aliases
declares alternative hostnames for the service on the network. Other containers on the same
network can use either the service name or an alias to connect to one of the service's containers.
Since aliases
are 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.
services:
some-service:
networks:
some-network:
aliases:
- alias1
- alias3
other-network:
aliases:
- alias2
In the following example, service frontend
is able to reach the backend
service at
the hostname backend
or database
on the back-tier
network. The service monitoring
is able to reach same backend
service at backend
or mysql
on the admin
network.
services:
frontend:
image: example/webapp
networks:
- front-tier
- back-tier
monitoring:
image: example/monitoring
networks:
- admin
backend:
image: example/backend
networks:
back-tier:
aliases:
- database
admin:
aliases:
- mysql
networks:
front-tier:
back-tier:
admin:
ipv4_address, ipv6_address
Specify a static IP address for a service container when joining the network.
The corresponding network configuration in the
top-level networks section must have an
ipam
attribute with subnet configurations covering each static address.
services:
frontend:
image: example/webapp
networks:
front-tier:
ipv4_address: 172.16.238.10
ipv6_address: 2001:3984:3989::10
networks:
front-tier:
ipam:
driver: default
config:
- subnet: "172.16.238.0/24"
- subnet: "2001:3984:3989::/64"
link_local_ips
link_local_ips
specifies 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.
Example:
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
mac_address
mac_address
sets the MAC address used by the service container when connecting to this particular network.
priority
priority
indicates in which order Compose connects 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.
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:
oom_kill_disable
If oom_kill_disable
is set, Compose configures the platform so it won't kill the container in case
of memory starvation.
oom_score_adj
oom_score_adj
tunes the preference for containers to be killed by platform in case of memory starvation. Value must
be within -1000,1000 range.
pid
pid
sets the PID mode for container created by Compose.
Supported values are platform specific.
pids_limit
pids_limit
tunes a container’s PIDs limit. Set to -1 for unlimited PIDs.
pids_limit: 10
When set, pids_limit
must be consistent with the pids
attribute in the
Deploy Specification.
platform
platform
defines the target platform the containers for the service run on. It uses the os[/arch[/variant]]
syntax.
The values of os
, arch
, and variant
must conform to the convention used by the
OCI Image Spec.
Compose uses this attribute to determine which version of the image is pulled and/or on which platform the service’s build is performed.
platform: darwin
platform: windows/amd64
platform: linux/arm64/v8
ports
The ports
is used to define the port mappings between the host machine and the containers. This is crucial for allowing external access to services running inside containers. It can be defined using short syntax for simple port mapping or long syntax, which includes additional options like protocol type and network mode.
Note
Port mapping must not be used with
network_mode: host
otherwise a runtime error occurs.
Short syntax
The short syntax is a colon-separated string to set the host IP, host port, and container port in the form:
[HOST:]CONTAINER[/PROTOCOL]
where:
HOST
is[IP:](port | range)
CONTAINER
isport | range
PROTOCOL
to restrict port to specified protocol.tcp
andudp
values are defined by the Specification, Compose offers support for platform-specific protocol names.
If host IP is not set, it binds to all network interfaces. Ports can be either a single value or a range. Host and container must use equivalent ranges.
Either specify both ports (HOST:CONTAINER
), or just the container port. In the latter case,
the container runtime automatically allocates any unassigned port of the host.
HOST:CONTAINER
should always be specified as a (quoted) string, to avoid conflicts
with
yaml base-60 float.
Examples:
ports:
- "3000"
- "3000-3005"
- "8000:8000"
- "9090-9091:8080-8081"
- "49100:22"
- "8000-9000:80"
- "127.0.0.1:8001:8001"
- "127.0.0.1:5000-5010:5000-5010"
- "6060:6060/udp"
Note
If Host IP mapping is not supported by a container engine, Compose rejects the Compose file and ignores the specified host IP.
Long syntax
The long form syntax allows the configuration of additional fields that can't be expressed in the short form.
target
: The container portpublished
: The publicly exposed port. It is defined as a string and can be set as a range using syntaxstart-end
. It means the actual port is assigned a remaining available port, within the set range.host_ip
: The Host IP mapping, unspecified means all network interfaces (0.0.0.0
).protocol
: The port protocol (tcp
orudp
). Defaults totcp
.app_protocol
: The application protocol (TCP/IP level 4 / OSI level 7) this port is used for. This is optional and can be used as a hint for Compose to offer richer behavior for protocols that it understands. Introduced in Docker Compose version 2.26.0.mode
:host
: For publishing a host port on each node, oringress
for a port to be load balanced. Defaults toingress
.name
: A human-readable name for the port, used to document it's usage within the service.
ports:
- name: web
target: 80
host_ip: 127.0.0.1
published: "8080"
protocol: tcp
app_protocol: http
mode: host
- name: web-secured
target: 443
host_ip: 127.0.0.1
published: "8083-9000"
protocol: tcp
app_protocol: https
mode: host
post_start
post_start
defines a sequence of lifecycle hooks to run after a container has started. The exact timing of when the command is run is not guaranteed.
command
: Specifies the command to run once the container starts. This attribute is required, and you can choose to use either the shell form or the exec form.user
: The user to run the command. If not set, the command is run with the same user as the main service command.privileged
: Lets thepost_start
command run with privileged access.working_dir
: The working directory in which to run the command. If not set, it is run in the same working directory as the main service command.environment
: Sets environment variables specifically for thepost_start
command. While the command inherits the environment variables defined for the service’s main command, this section lets you add new variables or override existing ones.
services:
test:
post_start:
- command: ./do_something_on_startup.sh
user: root
privileged: true
environment:
- FOO=BAR
For more information, see Use lifecycle hooks.
pre_stop
pre_stop
defines a sequence of lifecycle hooks to run before the container is stopped. These hooks won't run if the container stops by itself or is terminated suddenly.
Configuration is equivalent to `post_start.
privileged
privileged
configures the service container to run with elevated privileges. Support and actual impacts are platform specific.
profiles
profiles
defines a list of named profiles for the service to be enabled under. If unassigned, the service is always started but if assigned, it is only started if the profile is activated.
If present, profiles
follow the regex format of [a-zA-Z0-9][a-zA-Z0-9_.-]+
.
services:
frontend:
image: frontend
profiles: ["frontend"]
phpmyadmin:
image: phpmyadmin
depends_on:
- db
profiles:
- debug
pull_policy
pull_policy
defines the decisions Compose makes when it starts to pull images. Possible values are:
always
: Compose always pulls the image from the registry.never
: Compose doesn't pull the image from a registry and relies on the platform cached image. If there is no cached image, a failure is reported.missing
: Compose pulls the image only if it's not available in the platform cache. This is the default option if you are not also using the Compose Build Specification.if_not_present
is considered an alias for this value for backward compatibility.build
: Compose builds the image. Compose rebuilds the image if it's already present.
read_only
read_only
configures the service container to be created with a read-only filesystem.
restart
restart
defines the policy that the platform applies on container termination.
no
: The default restart policy. It does not restart the container under any circumstances.always
: The policy always restarts the container until its removal.on-failure[:max-retries]
: The policy restarts the container if the exit code indicates an error. Optionally, limit the number of restart retries the Docker daemon attempts.unless-stopped
: The policy restarts the container irrespective of the exit code but stops restarting when the service is stopped or removed.
restart: "no"
restart: always
restart: on-failure
restart: on-failure:3
restart: unless-stopped
You can find more detailed information on restart policies in the Restart Policies (--restart) section of the Docker run reference page.
runtime
runtime
specifies which runtime to use for the service’s containers.
For example, runtime
can be the name of
an implementation of OCI Runtime Spec, such as "runc".
web:
image: busybox:latest
command: true
runtime: runc
The default is runc
. To use a different runtime, see
Alternative runtimes.
scale
scale
specifies the default number of containers to deploy for this service.
When both are set, scale
must be consistent with the replicas
attribute in the
Deploy Specification.
secrets
The secrets
attribute grants access to sensitive data defined by the secrets top-level element on a per-service basis. Services can be granted access to multiple secrets.
Two different syntax variants are supported; the short syntax and the long syntax. Long and short syntax for secrets may be used in the same Compose file.
Compose reports an error if the secret doesn't exist on the platform or isn't defined in the
secrets
top-level section of the Compose file.
Defining a secret in the top-level secrets
must not imply granting any service access to it.
Such grant must be explicit within service specification as
secrets service element.
Short syntax
The short syntax variant only specifies the secret name. This grants the
container access to the secret and mounts it as read-only to /run/secrets/<secret_name>
within the container. The source name and destination mountpoint are both set
to the secret name.
The following example uses the short syntax to grant the frontend
service
access to the server-certificate
secret. The value of server-certificate
is set
to the contents of the file ./server.cert
.
services:
frontend:
image: example/webapp
secrets:
- server-certificate
secrets:
server-certificate:
file: ./server.cert
Long syntax
The long syntax provides more granularity in how the secret is created within the service's containers.
source
: The name of the secret as it exists on the platform.target
: The name of the file to be mounted in/run/secrets/
in the service's task container, or absolute path of the file if an alternate location is required. Defaults tosource
if not specified.uid
andgid
: The numeric UID or GID that owns the file within/run/secrets/
in the service's task containers. Default value is USER running container.mode
: The permissions for the file to be mounted in/run/secrets/
in the service's task containers, in octal notation. The default value is world-readable permissions (mode0444
). The writable bit must be ignored if set. The executable bit may be set.
The following example sets the name of the server-certificate
secret file to server.cert
within the container, sets the mode to 0440
(group-readable), and sets the user and group
to 103
. The value of server-certificate
is set
to the contents of the file ./server.cert
.
services:
frontend:
image: example/webapp
secrets:
- source: server-certificate
target: server.cert
uid: "103"
gid: "103"
mode: "0440"
secrets:
server-certificate:
file: ./server.cert
security_opt
security_opt
overrides the default labeling scheme for each container.
security_opt:
- label:user:USER
- label:role:ROLE
For further default labeling schemes you can override, see Security configuration.
shm_size
shm_size
configures the size of the shared memory (/dev/shm
partition on Linux) allowed by the service container.
It's specified as a
byte value.
stdin_open
stdin_open
configures a service's container to run with an allocated stdin. This is the same as running a container with the
-i
flag. For more information, see
Keep STDIN open.
Supported values are true
or false
.
stop_grace_period
stop_grace_period
specifies how long Compose must wait when attempting to stop a container if it doesn't
handle SIGTERM (or whichever stop signal has been specified with
stop_signal
), before sending SIGKILL. It's specified
as a
duration.
stop_grace_period: 1s
stop_grace_period: 1m30s
Default value is 10 seconds for the container to exit before sending SIGKILL.
stop_signal
stop_signal
defines the signal that Compose uses to stop the service containers.
If unset containers are stopped by Compose by sending SIGTERM
.
stop_signal: SIGUSR1
storage_opt
storage_opt
defines storage driver options for a service.
storage_opt:
size: '1G'
sysctls
sysctls
defines kernel parameters to set in the container. sysctls
can use either an array or a map.
sysctls:
net.core.somaxconn: 1024
net.ipv4.tcp_syncookies: 0
sysctls:
- net.core.somaxconn=1024
- net.ipv4.tcp_syncookies=0
You can only use sysctls that are namespaced in the kernel. Docker does not support changing sysctls inside a container that also modify the host system. For an overview of supported sysctls, refer to configure namespaced kernel parameters (sysctls) at runtime.
tmpfs
tmpfs
mounts a temporary file system inside the container. It can be a single value or a list.
tmpfs: /run
tmpfs:
- /run
- /tmp
tty
tty
configures a service's container to run with a TTY. This is the same as running a container with the
-t
or --tty
flag. For more information, see
Allocate a pseudo-TTY.
Supported values are true
or false
.
ulimits
ulimits
overrides the default ulimits for a container. It's specified either as an integer for a single limit
or as mapping for soft/hard limits.
ulimits:
nproc: 65535
nofile:
soft: 20000
hard: 40000
user
user
overrides the user used to run the container process. The default is set by the image (i.e. Dockerfile USER
). If it's not set, then root
.
userns_mode
userns_mode
sets the user namespace for the service. Supported values are platform specific and may depend
on platform configuration.
userns_mode: "host"
uts
uts
configures the UTS namespace mode set for the service container. When unspecified
it is the runtime's decision to assign a UTS namespace, if supported. Available values are:
'host'
: Results in the container using the same UTS namespace as the host.
uts: "host"
volumes
The volumes
attribute define mount host paths or named volumes that are accessible by service containers. You can use volumes
to define multiple types of mounts; volume
, bind
, tmpfs
, or npipe
.
If the mount is a host path and is only used by a single service, it can be declared as part of the service
definition. To reuse a volume across multiple services, a named
volume must be declared in the volumes
top-level element.
The following example shows a named volume (db-data
) being used by the backend
service,
and a bind mount defined for a single service.
services:
backend:
image: example/backend
volumes:
- type: volume
source: db-data
target: /data
volume:
nocopy: true
subpath: sub
- type: bind
source: /var/run/postgres/postgres.sock
target: /var/run/postgres/postgres.sock
volumes:
db-data:
For more information about the volumes
top-level element, see
Volumes.
Short syntax
The short syntax uses a single string with colon-separated values to specify a volume mount
(VOLUME:CONTAINER_PATH
), or an access mode (VOLUME:CONTAINER_PATH:ACCESS_MODE
).
VOLUME
: Can be either a host path on the platform hosting containers (bind mount) or a volume name.CONTAINER_PATH
: The path in the container where the volume is mounted.ACCESS_MODE
: A comma-separated,
list of options:rw
: Read and write access. This is the default if none is specified.ro
: Read-only access.z
: SELinux option indicating that the bind mount host content is shared among multiple containers.Z
: SELinux option indicating that the bind mount host content is private and unshared for other containers.
Note
The SELinux re-labeling bind mount option is ignored on platforms without SELinux.
Note
Relative host paths are only supported by Compose that deploy to a local container runtime. This is because the relative path is resolved from the Compose file’s parent directory which is only applicable in the local case. When Compose deploys to a non-local platform it rejects Compose files which use relative host paths with an error. To avoid ambiguities with named volumes, relative paths should always begin with
.
or..
.
Long syntax
The long form syntax allows the configuration of additional fields that can't be expressed in the short form.
type
: The mount type. Eithervolume
,bind
,tmpfs
,npipe
, orcluster
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-levelvolumes
key. 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
: Used to configure additional bind options:propagation
: The propagation mode used for the bind.create_host_path
: Creates a directory at the source path on host if there is nothing present. Compose does nothing if there is something present at the path. This is automatically implied by short syntax for backward compatibility withdocker-compose
legacy.selinux
: The SELinux re-labeling optionz
(shared) orZ
(private)
volume
: Configures additional volume options:nocopy
: Flag to disable copying of data from a container when a volume is created.subpath
: Path inside a volume to mount instead of the volume root.
tmpfs
: Configures additional tmpfs options:size
: The size for the tmpfs mount in bytes (either numeric or as bytes unit).mode
: The file mode for the tmpfs mount as Unix permission bits as an octal number. Introduced in Docker Compose version 2.14.0.
consistency
: The consistency requirements of the mount. Available values are platform specific.
Tip
Working with large repositories or monorepos, or with virtual file systems that are no longer scaling with your codebase? Compose now takes advantage of Synchronized file shares and automatically creates file shares for bind mounts. Ensure you're signed in to Docker with a paid subscription and have enabled both Access experimental features and Manage Synchronized file shares with Compose in Docker Desktop's settings.
volumes_from
volumes_from
mounts all of the volumes from another service or container. You can optionally specify
read-only access ro
or read-write rw
. If no access level is specified, then read-write access is used.
You can also mount volumes from a container that is not managed by Compose by using the container:
prefix.
volumes_from:
- service_name
- service_name:ro
- container:container_name
- container:container_name:rw
working_dir
working_dir
overrides the container's working directory which is specified by the image, for example Dockerfile's WORKDIR
.