Unable to use variable substitution in docker-compose - docker

Question

I use a mac to run docker and hence I am dependent on boot2docker or docker-machine . My application running in the container needs the docker host's ip.
I saw that the variable substitution feature of docker-compose is exactly what I need . When I try something like the below it works fine
extra_hosts:
- "somehost:162.242.195.82"
BUT when I try something like:
export DOCKER_HOST="64.88.225.66"
extra_hosts:
- "host:${DOCKER_HOST}"
I get :
$ docker-compose build --no-cache
Traceback (most recent call last):
File "<string>", line 3, in <module>
File "/code/compose/cli/main.py", line 54, in main
File "/code/compose/cli/docopt_command.py", line 23, in sys_dispatch
File "/code/compose/cli/docopt_command.py", line 26, in dispatch
File "/code/compose/cli/main.py", line 169, in perform_command
File "/code/compose/cli/command.py", line 53, in project_from_options
File "/code/compose/cli/command.py", line 89, in get_project
File "/code/compose/cli/command.py", line 70, in get_client
File "/code/compose/cli/docker_client.py", line 28, in docker_client
File "/code/.tox/py27/lib/python2.7/site-packages/docker/client.py", line 58, in __init__
File "/code/.tox/py27/lib/python2.7/site-packages/docker/utils/utils.py", line 362, in parse_host
docker.errors.DockerException: Bind address needs a port: 64.88.225.66
docker-compose returned -1
I'm not sure why it wants a port. It wasn't happy when I gave it a port number too.
So, how can I get my docker host ip to my container? It would be nice if i can pass commands like boot2docker ip or docker-machine ip default in the extra_hosts section or maybe if docker-compose could execute a script to get this value it would be great !

Answer 1

The problem is that DOCKER_HOST is a variable used by docker-compose itself (https://docs.docker.com/compose/reference/overview/#docker-host) and the format is wrong (it needs a tcp:// scheme and a port I believe).
You'll have to choose a different variable to include it in extra_hosts:.
Otherwise you could just pass it in as an environment variable (environment: [DOCKER_HOST=]) and parse the ip address out of it in the container.