Host environment variables with docker stack deploy

Question

I was wondering if there is a way to use environment variables taken from the host where the container is deployed, instead of the ones taken from where the docker stack deploy command is executed. For example imagine the following docker-compose.yml launched on three node Docker Swarm cluster:

version: '3.2'
services:
  kafka:
    image: wurstmeister/kafka
    ports:
      - target: 9094
        published: 9094
        protocol: tcp
        mode: host
    deploy:
      mode: global
    environment:
      KAFKA_JMX_OPTS: "-Djava.rmi.server.hostname=${JMX_HOSTNAME} -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.rmi.port=1099"

The JMX_HOSTNAME should be taken from the host where the container is actually deployed and should not be the same value for every container. Is there a correct way to do this?

Answer 1

Yes, this works when you combine two concepts:

1. Swarm node labels, of which Hostname is one of the built-in ones.
2. Swarm service go templates, which also work in stack files.

This would pull in the hostname to the ENV value of DUDE for each container to be the host that it's running on:

version: '3.4'

services:
  nginx:
    image: nginx
    environment:
      DUDE: "{{.Node.Hostname}}"
    deploy:
      replicas: 3

Answer 2

It works if you run the docker command through env.

env JMX_HOSTNAME="${JMX_HOSTNAME}" docker stack deploy -c docker-compose.yml mystack

Credit to GitHub issue that pointed me in the right direction.