docker-compose scale - agent instance id

Question

When I use docker-compose scale I would like to have an instance id used in the yml file.

docker-compose.yml:

myservice:
  volumes:
  - ./volumes/foo{AGENT_ID}/bar:/foo/bar

I have seen a lot of discussions around this topic but I still have not found a clear answer.

Is there an environment variable or similar that I can use this way? It would be ideal if I could use that in bash scripts, etc.

Answer 1

I am aware that this might not be a perfect solution but if you don't mind sharing data between nodes.. it does work well. I am using this for local tests so it is safe in my case.

Docker-compose.yml

...
volumes:
   - /var/run/docker.sock:/var/run/docker.sock
...

Dockerfile

...
RUN pip3 install docker
...

In each node, I deploy the following script get_name.py

from docker import Client
import os

hostname = os.environ['HOSTNAME']

cli = Client(base_url='unix://var/run/docker.sock')
data = cli.containers()

for d in data:
    id = d['Id'][:12]
    names = d['Names']
    if id == hostname:
        print(names[0])
        quit()

print(hostname)

And when the node starts (start.sh), it queries its name and creates a symlink to the corresponding subdirectory:

...
NODE_NAME=$(python /root/scripts/get_name.py)
OWN_VOLUME_NAME="/shared_volumes${NODE_NAME}"
ln -s ${OWN_VOLUME_NAME} /data
...