--- layout: default title: docker-compose.yml reference page_title: docker-compose.yml reference page_description: docker-compose.yml reference page_keywords: fig, composition, compose, docker --- # docker-compose.yml reference 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`. ### image 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 ``` ### build 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 ``` ### dockerfile Alternate Dockerfile. Compose will use an alternate file to build with. ``` dockerfile: Dockerfile-alternate ``` ### command Override the default command. ``` command: bundle exec thin -p 3000 ``` ### links 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](env.md) for details. ### external_links Link to containers started outside this `docker-compose.yml` or even outside of Compose, especially for containers that provide shared or common services. `external_links` follow semantics similar to `links` when specifying both the container name and the link alias (`CONTAINER:ALIAS`). ``` external_links: - redis_1 - project_db_1:mysql - project_db_1:postgresql ``` ### extra_hosts Add hostname mappings. Use the same values as the docker client `--add-host` parameter. ``` extra_hosts: - "somehost:162.242.195.82" - "otherhost:50.31.209.229" ``` An entry with the ip address and hostname will be created in `/etc/hosts` inside containers for this service, e.g: ``` 162.242.195.82 somehost 50.31.209.229 otherhost ``` ### ports Expose ports. Either specify both ports (`HOST:CONTAINER`), or just the container port (a random host port will be chosen). > **Note:** When mapping ports in the `HOST:CONTAINER` format, you may experience > erroneous results when using a container port lower than 60, because YAML will > parse numbers in the format `xx:yy` as sexagesimal (base 60). For this reason, > we recommend always explicitly specifying your port mappings as strings. ``` ports: - "3000" - "8000:8000" - "49100:22" - "127.0.0.1:8001:8001" ``` ### expose Expose ports without publishing them to the host machine - they'll only be accessible to linked services. Only the internal port can be specified. ``` expose: - "3000" - "8000" ``` ### volumes 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 ``` ### volumes_from Mount all of the volumes from another service or container. ``` volumes_from: - service_name - container_name ``` ### environment Add environment variables. You can use either an array or a dictionary. 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 SESSION_SECRET: environment: - RACK_ENV=development - SESSION_SECRET ``` ### env_file Add environment variables from a file. Can be a single value or a list. If you have specified a Compose file with `docker-compose -f FILE`, paths in `env_file` are relative to the directory that file is in. Environment variables specified in `environment` override these values. ``` env_file: .env env_file: - ./common.env - ./apps/web.env - /opt/secrets.env ``` Compose expects each line in an env file to be in `VAR=VAL` format. Lines beginning with `#` (i.e. comments) are ignored, as are blank lines. ``` # Set Rails/Rack environment RACK_ENV=development ``` ### extends 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. For more on `extends`, see the [tutorial](extends.md#example) and [reference](extends.md#reference). ### labels Add metadata to containers using [Docker labels](http://docs.docker.com/userguide/labels-custom-metadata/). 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" ``` ### log driver Specify a logging driver for the service's containers, as with the ``--log-driver`` option for docker run ([documented here](http://docs.docker.com/reference/run/#logging-drivers-log-driver)). Allowed values are currently ``json-file``, ``syslog`` and ``none``. The list will change over time as more drivers are added to the Docker engine. The default value is json-file. ``` log_driver: "json-file" log_driver: "syslog" log_driver: "none" ``` ### net Networking mode. Use the same values as the docker client `--net` parameter. ``` net: "bridge" net: "none" net: "container:[name or id]" net: "host" ``` ### pid ``` pid: "host" ``` Sets the PID mode to the host PID mode. This turns on sharing between container and the host operating system the PID address space. Containers launched with this flag will be able to access and manipulate other containers in the bare-metal machine's namespace and vise-versa. ### dns Custom DNS servers. Can be a single value or a list. ``` dns: 8.8.8.8 dns: - 8.8.8.8 - 9.9.9.9 ``` ### cap_add, cap_drop Add or drop container capabilities. See `man 7 capabilities` for a full list. ``` cap_add: - ALL cap_drop: - NET_ADMIN - SYS_ADMIN ``` ### dns_search Custom DNS search domains. Can be a single value or a list. ``` dns_search: example.com dns_search: - dc1.example.com - dc2.example.com ``` ### devices List of device mappings. Uses the same format as the `--device` docker client create option. ``` devices: - "/dev/ttyUSB0:/dev/ttyUSB0" ``` ### security_opt Override the default labeling scheme for each container. ``` security_opt: - label:user:USER - label:role:ROLE ``` ### working\_dir, entrypoint, user, hostname, domainname, mem\_limit, privileged, restart, stdin\_open, tty, cpu\_shares, cpuset, read\_only Each of these is a single value, analogous to its [docker run](https://docs.docker.com/reference/run/) counterpart. ``` cpu_shares: 73 cpuset: 0,1 working_dir: /code entrypoint: /code/entrypoint.sh user: postgresql hostname: foo domainname: foo.com mem_limit: 1000000000 privileged: true restart: always stdin_open: true tty: true read_only: true ``` ## Compose documentation - [User guide](index.md) - [Installing Compose](install.md) - [Get started with Django](django.md) - [Get started with Rails](rails.md) - [Get started with Wordpress](wordpress.md) - [Command line reference](cli.md) - [Compose environment variables](env.md) - [Compose command line completion](completion.md)