docker-compose/docs/yml.md

---

layout: default

title: fig.yml reference

fig.yml reference

Each service defined in fig.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 fig.yml.

-- Tag or partial image ID. Can be local or remote - Fig will attempt to pull if it doesn't exist locally.
image: ubuntu
image: orchardup/postgresql
image: a4bc65fd

-- Path to a directory containing a Dockerfile. Fig will build and tag it with a generated name, and use that image thereafter.
build: /path/to/build/dir

-- Override the default command.
command: bundle exec thin -p 3000

-- Link to containers in another service (see "Communicating between containers").
links:
 - db
 - redis

-- 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 format HOST:CONTAINER you may experience erroneous results when using a container port lower than 60. This is due to YAML parsing numbers in the format "xx:yy" as sexagesimal (base 60) for this reason it is recommended to define your port mappings as strings.
ports:
 - "3000"
 - "8000:8000"
 - "49100:22"

-- Map volumes from the host machine (HOST:CONTAINER).
volumes:
 - cache/:/tmp/cache

-- Add environment variables.
environment:
  RACK_ENV: development