The compose file is a YAML file where all the top level
keys are the name of a service, and the values are the service definition.
The default path for a compose file is ./docker-compose.yml.
Each service defined in docker-compose.yml must specify exactly one of
image or build. Other keys are optional, and are analogous to their
docker run command-line counterparts.
As with docker run, options specified in the Dockerfile (e.g., CMD,
EXPOSE, VOLUME, ENV) are respected by default - you don't need to
specify them again in docker-compose.yml.
Path to a directory containing a Dockerfile. When the value supplied is a relative path, it is interpreted as relative to the location of the yml file itself. This directory is also the build context that is sent to the Docker daemon.
Compose will build and tag it with a generated name, and use that image thereafter.
build: /path/to/build/dir
Using build together with image is not allowed. Attempting to do so results in an error.
Add or drop container capabilities.
See man 7 capabilities for a full list.
cap_add:
- ALL
cap_drop:
- NET_ADMIN
- SYS_ADMIN
Override the default command.
command: bundle exec thin -p 3000
Specify an optional parent cgroup for the container.
cgroup_parent: m-executor-abcd
Specify a custom container name, rather than a generated default name.
container_name: my-web-container
Because Docker container names must be unique, you cannot scale a service beyond 1 container if you have specified a custom name. Attempting to do so results in an error.
List of device mappings. Uses the same format as the --device docker
client create option.
devices:
- "/dev/ttyUSB0:/dev/ttyUSB0"
Custom DNS servers. Can be a single value or a list.
dns: 8.8.8.8
dns:
- 8.8.8.8
- 9.9.9.9
Custom DNS search domains. Can be a single value or a list.
dns_search: example.com
dns_search:
- dc1.example.com
- dc2.example.com
Alternate Dockerfile.
Compose will use an alternate file to build with.
dockerfile: Dockerfile-alternate
Using dockerfile together with image is not allowed. Attempting to do so results in an error.
Add environment variables from a file. Can be a single value or a list.
If you have specified a Compose file with docker-compose -f FILE, paths in
env_file are relative to the directory that file is in.
Environment variables specified in environment override these values.
env_file: .env
env_file:
- ./common.env
- ./apps/web.env
- /opt/secrets.env
Compose expects each line in an env file to be in VAR=VAL format. Lines
beginning with # (i.e. comments) are ignored, as are blank lines.
# Set Rails/Rack environment
RACK_ENV=development
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
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.
Here's a simple example. Suppose we have 2 files - common.yml and
development.yml. We can use extends to define a service in
development.yml which uses configuration defined in common.yml:
common.yml
webapp:
build: ./webapp
environment:
- DEBUG=false
- SEND_EMAILS=false
development.yml
web:
extends:
file: common.yml
service: webapp
ports:
- "8000:8000"
links:
- db
environment:
- DEBUG=true
db:
image: postgres
Here, the web service in development.yml inherits the configuration of
the webapp service in common.yml - the build and environment keys -
and adds ports and links configuration. It overrides one of the defined
environment variables (DEBUG) with a new value, and the other one
(SEND_EMAILS) is left untouched.
The file key is optional, if it is not set then Compose will look for the
service within the current file.
For more on extends, see the tutorial and
reference.
Link to containers started outside this docker-compose.yml or even outside
of Compose, especially for containers that provide shared or common services.
external_links follow semantics similar to links when specifying both the
container name and the link alias (CONTAINER:ALIAS).
external_links:
- redis_1
- project_db_1:mysql
- project_db_1:postgresql
Add hostname mappings. Use the same values as the docker client --add-host parameter.
extra_hosts:
- "somehost:162.242.195.82"
- "otherhost:50.31.209.229"
An entry with the ip address and hostname will be created in /etc/hosts inside containers for this service, e.g:
162.242.195.82 somehost
50.31.209.229 otherhost
Tag or partial image ID. Can be local or remote - Compose will attempt to pull if it doesn't exist locally.
image: ubuntu
image: orchardup/postgresql
image: a4bc65fd
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
the link alias (SERVICE:ALIAS), or just the service name (which will also be
used for the alias).
links:
- db
- db:database
- redis
An entry with the alias' name will be created in /etc/hosts inside containers
for this service, e.g:
172.17.2.186 db
172.17.2.186 database
172.17.2.187 redis
Environment variables will also be created - see the environment variable reference for details.
Specify a logging driver for the service's containers, as with the --log-driver
option for docker run (documented here).
The default value is json-file.
log_driver: "json-file"
log_driver: "syslog"
log_driver: "none"
Note: Only the
json-filedriver makes the logs available directly fromdocker-compose upanddocker-compose logs. Using any other driver will not print any logs.
Specify logging options with log_opt for the logging driver, as with the --log-opt option for docker run.
Logging options are key value pairs. An example of syslog options:
log_driver: "syslog"
log_opt:
syslog-address: "tcp://192.168.0.42:123"
Networking mode. Use the same values as the docker client --net parameter.
net: "bridge"
net: "none"
net: "container:[name or id]"
net: "host"
pid: "host"
Sets the PID mode to the host PID mode. This turns on sharing between container and the host operating system the PID address space. Containers launched with this flag will be able to access and manipulate other containers in the bare-metal machine's namespace and vise-versa.
Expose ports. Either specify both ports (HOST:CONTAINER), or just the container
port (a random host port will be chosen).
Note: When mapping ports in the
HOST:CONTAINERformat, you may experience erroneous results when using a container port lower than 60, because YAML will parse numbers in the formatxx:yyas sexagesimal (base 60). For this reason, we recommend always explicitly specifying your port mappings as strings.
ports:
- "3000"
- "3000-3005"
- "8000:8000"
- "9090-9091:8080-8081"
- "49100:22"
- "127.0.0.1:8001:8001"
- "127.0.0.1:5000-5010:5000-5010"
Override the default labeling scheme for each container.
security_opt:
- label:user:USER
- label:role:ROLE
Mount paths as volumes, optionally specifying a path on the host machine
(HOST:CONTAINER), or an access mode (HOST:CONTAINER:ro).
volumes:
- /var/lib/mysql
- ./cache:/tmp/cache
- ~/configs:/etc/configs/:ro
You can mount a relative path on the host, which will expand relative to
the directory of the Compose configuration file being used. Relative paths
should always begin with . or ...
If you use a volume name (instead of a volume path), you may also specify
a volume_driver.
volume_driver: mydriver
Note: No path expansion will be done if you have also specified a
volume_driver.
See Docker Volumes and Volume Plugins for more information.
Mount all of the volumes from another service or container, optionally
specifying read-only access(ro) or read-write(rw).
volumes_from:
- service_name
- container_name
- service_name:rw
cpu_shares, cpuset, domainname, entrypoint, hostname, ipc, mac_address, mem_limit, memswap_limit, privileged, read_only, restart, stdin_open, tty, user, working_dir
Each of these is a single value, analogous to its docker run counterpart.
cpu_shares: 73
cpuset: 0,1
entrypoint: /code/entrypoint.sh
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
stdin_open: true
tty: true
Your configuration options can contain environment variables. Compose uses the
variable values from the shell environment in which docker-compose is run. For
example, suppose the shell contains POSTGRES_VERSION=9.3 and you supply this
configuration:
db:
image: "postgres:${POSTGRES_VERSION}"
When you run docker-compose up with this configuration, Compose looks for the
POSTGRES_VERSION environment variable in the shell and substitutes its value
in. For this example, Compose resolves the image to postgres:9.3 before
running the configuration.
If an environment variable is not set, Compose substitutes with an empty
string. In the example above, if POSTGRES_VERSION is not set, the value for
the image option is postgres:.
Both $VARIABLE and ${VARIABLE} syntax are supported. Extended shell-style
features, such as ${VARIABLE-default} and ${VARIABLE/foo/bar}, are not
supported.
You can use a $$ (double-dollar sign) when your configuration needs a literal
dollar sign. This also prevents Compose from interpolating a value, so a $$
allows you to refer to environment variables that you don't want processed by
Compose.
web:
build: .
command: "$$VAR_NOT_INTERPOLATED_BY_COMPOSE"
If you forget and use a single dollar sign ($), Compose interprets the value as an environment variable and will warn you:
The VAR_NOT_INTERPOLATED_BY_COMPOSE is not set. Substituting an empty string.