---
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`.

```yaml
-- 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).
ports:
 - 3000
 - 8000:8000

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

-- Add environment variables.
environment:
  RACK_ENV: development
```