Compose file version 1 referenceEstimated reading time: 16 minutes
Reference and guidelines
These topics describe version 1 of the Compose file format. This is the oldest version.
Compose and Docker compatibility matrix
There are several versions of the Compose file format – 1, 2, 2.x, and 3.x The table below is a quick look. For full details on what each version includes and how to upgrade, see About versions and upgrading.
This table shows which Compose file versions support specific Docker releases.
|Compose file format||Docker Engine release|
In addition to Compose file format versions shown in the table, the Compose itself is on a release schedule, as shown in Compose releases, but file format versions do not necessarily increment with each release. For example, Compose file format 3.0 was first introduced in Compose release 1.10.0, and versioned gradually in subsequent releases.
Service configuration reference
The default path for a Compose file is
Tip: You can use either a
.yamlextension for this file. They both work.
A service definition contains configuration which is applied to each
container started for that service, much like passing command-line parameters to
docker run, options specified in the Dockerfile, such as
ENV, are respected by default - you don’t need to
specify them again in
This section contains a list of all configuration options supported by a service definition in version 1.
Configuration options that are applied at build time.
build can specified as a string containing a path to the build
In version 1 file format,
buildis different in two ways:
- Only the string form (
build: .) is allowed - not the object form that is allowed in Version 2 and up.
imageis not allowed. Attempting to do so results in an error.
Compose uses an alternate file to build with. A build path must also be specified.
build: . dockerfile: Dockerfile-alternate
In the version 1 file format,
dockerfileis different from newer versions in two ways:
- It appears alongside
build, not as a sub-option:
imageis not allowed. Attempting to do so results in an error.
Add or drop container capabilities.
man 7 capabilities for a full list.
cap_add: - ALL cap_drop: - NET_ADMIN - SYS_ADMIN
Note: These options are ignored when deploying a stack in swarm mode with a (version 3) Compose file.
Override the default command.
command: bundle exec thin -p 3000
The command can also be a list, in a manner similar to dockerfile:
command: ["bundle", "exec", "thin", "-p", "3000"]
Specify an optional parent cgroup for the container.
Specify a custom container name, rather than a generated default name.
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.
List of device mappings. Uses the same format as the
client create option.
devices: - "/dev/ttyUSB0:/dev/ttyUSB0"
Custom DNS servers. Can be a single value or a list.
dns: - 126.96.36.199 - 188.8.131.52
Custom DNS search domains. Can be a single value or a list.
dns_search: - dc1.example.com - dc2.example.com
Override the default entrypoint.
The entrypoint can also be a list, in a manner similar to dockerfile:
entrypoint: ["php", "-d", "memory_limit=-1", "vendor/bin/phpunit"]
entrypointboth overrides any default entrypoint set on the service’s image with the
ENTRYPOINTDockerfile instruction, and clears out any default command on the image - meaning that if there’s a
CMDinstruction in the Dockerfile, it is ignored.
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 section override these values – this holds true even if those values are empty or undefined.
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
# are processed as comments and are ignored. Blank lines are
# Set Rails/Rack environment RACK_ENV=development
Note: If your service specifies a build option, variables defined in environment files are not automatically visible during the build.
The value of
VAL is used as is and not modified at all. For example if the
value is surrounded by quotes (as is often the case of shell variables), the
quotes are included in the value passed to Compose.
Keep in mind that the order of files in the list is significant in determining
the value assigned to a variable that shows up more than once. The files in the
list are processed from the top down. For the same variable specified in file
a.env and assigned a different value in file
listed below (after), then the value from
b.env stands. For example, given the
following declaration in
services: some-service: env_file: - a.env - b.env
And the following files:
# a.env VAR=1
# b.env VAR=hello
Add environment variables. You can use either an array or a dictionary. Any boolean values (true, false, yes, no) need to be enclosed in quotes to ensure they are not converted to True or False by the YML parser.
Environment variables with only a key are resolved to their values on the machine Compose is running on, which can be helpful for secret or host-specific values.
environment: RACK_ENV: development SHOW: 'true' SESSION_SECRET:
environment: - RACK_ENV=development - SHOW=true - SESSION_SECRET
Note: If your service specifies a build option, variables defined in
environmentare not automatically visible during the build.
Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.
expose: - "3000" - "8000"
Extend another service, in the current file or another, optionally overriding configuration.
You can use
extends on any service together with other configuration keys.
extends value must be a dictionary defined with a required
and an optional
extends: file: common.yml service: webapp
service the name of the service being extended, for example
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
You can extend a service that itself extends another. You can extend
indefinitely. Compose does not support circular references and
returns an error if it encounters one.
For more on
extends, see the
the extends documentation.
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
specifying both the container name and the link alias (
external_links: - redis_1 - project_db_1:mysql - project_db_1:postgresql
Add hostname mappings. Use the same values as the docker client
extra_hosts: - "somehost:184.108.40.206" - "otherhost:220.127.116.11"
An entry with the ip address and hostname is created in
/etc/hosts inside containers for this service, e.g:
18.104.22.168 somehost 22.214.171.124 otherhost
Specify the image to start the container from. Can either be a repository/tag or a partial image ID.
If the image does not exist, Compose attempts to pull it, unless you have also specified build, in which case it builds it using the specified options and tags it with the specified tag.
Add metadata to containers using Docker labels. You can use either an array or a dictionary.
It’s recommended that you use reverse-DNS notation to prevent your labels from conflicting with those used by other software.
labels: com.example.description: "Accounting webapp" com.example.department: "Finance" com.example.label-with-empty-value: ""
labels: - "com.example.description=Accounting webapp" - "com.example.department=Finance" - "com.example.label-with-empty-value"
Link to containers in another service. Either specify both the service name and
a link alias (
"SERVICE:ALIAS"), or just the service name.
Links are a legacy option. We recommend using networks instead.
web: links: - "db" - "db:database" - "redis"
Containers for the linked service are reachable at a hostname identical to the alias, or the service name if no alias was specified.
Links also express dependency between services in the same way as depends_on, so they determine the order of service startup.
If you define both links and networks, services with links between them must share at least one network in common in order to communicate.
Specify a log driver. The default is
Specify logging options as key-value pairs. An example of
log_opt: syslog-address: "tcp://192.168.0.42:123"
Network mode. Use the same values as the docker client
container:... form can take a service name instead of a container name or
net: "service:[service name]"
net: "container:[container name/id]"
Sets the PID mode to the host PID mode. This turns on sharing between container and the host operating system the PID address space. Containers launched with this flag can access and manipulate other containers in the bare-metal machine’s namespace and vice versa.
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:CONTAINERformat, you may experience erroneous results when using a container port lower than 60, because YAML parses numbers in the format
xx:yyas a base-60 value. For this reason, we recommend always explicitly specifying your port mappings as strings.
ports: - "3000" - "3000-3005" - "8000:8000" - "9090-9091:8080-8081" - "49100:22" - "127.0.0.1:8001:8001" - "127.0.0.1:5000-5010:5000-5010" - "6060:6060/udp" - "12400-12500:1240"
Override the default labeling scheme for each container.
security_opt: - label:user:USER - label:role:ROLE
Sets an alternative signal to stop the container. By default
SIGTERM. Setting an alternative signal using
stop to send that signal instead.
Override the default ulimits for a container. You can either specify a single limit as an integer or soft/hard limits as a mapping.
ulimits: nproc: 65535 nofile: soft: 20000 hard: 40000
Mount paths or named volumes, optionally specifying a path on the host machine
HOST:CONTAINER), or an access mode (
For version 2 files, named volumes need to be specified with the
When using version 1, the Docker Engine creates the named
volume automatically if it doesn’t exist.
You can mount a relative path on the host, which expands relative to
the directory of the Compose configuration file being used. Relative paths
should always begin with
volumes: # Just specify a path and let the Engine create a volume - /var/lib/mysql # Specify an absolute path mapping - /opt/data:/var/lib/mysql # Path on the host, relative to the Compose file - ./cache:/tmp/cache # User-relative path - ~/configs:/etc/configs/:ro # Named volume - datavolume:/var/lib/mysql
If you do not use a host path, you may specify a
There are several things to note, depending on which Compose file version you’re using:
- For version 1 files, both named volumes and container volumes use the specified driver.
- No path expansion is done if you have also specified a
volume_driver. For example, if you specify a mapping of
./foopart is passed straight to the volume driver without being expanded.
Mount all of the volumes from another service or container, optionally
specifying read-only access (
ro) or read-write (
rw). If no access level
is specified, then read-write is used.
volumes_from: - service_name - service_name:ro
cpu_shares, cpu_quota, cpuset, domainname, hostname, ipc, mac_address, mem_limit, memswap_limit, mem_swappiness, privileged, read_only, restart, shm_size, stdin_open, tty, user, working_dir
Each of these is a single value, analogous to its docker run counterpart.
cpu_shares: 73 cpu_quota: 50000 cpuset: 0,1 user: postgresql working_dir: /code domainname: foo.com hostname: foo ipc: host mac_address: 02:42:ac:11:65:43 mem_limit: 1000000000 memswap_limit: 2000000000 privileged: true restart: always read_only: true shm_size: 64M stdin_open: true tty: true