Usually, when launching Docker containers we don’t really know or care what IP address a specific container will be given. If proper service discovery and registration is configured, we just launch containers as needed and they make it into the application ecosystem seamlessly. Recently, I was working on a very edge-case multi-container application where every container needed to know (or be able to predict) every other containers’ IP address at run time. This was not a cascaded need where successor containers learn predecessors’ IP addresses, but more like a full mesh.

In Docker Engine 1.10 the docker run command received a new flag namely the --ip flag. This allows you to define a static IP address for a container at run time. Unfortunately, Docker Compose (1.6.2) did not support this option. I guess we can think of Engine as being upstream of Compose, so some new Engine features take a while to make it into Compose. Luckily, this has already made it into mainline dev for Compose and is earmarked for release with the 1.7.0 milestone (which should coincide with Engine 1.11). Find the commit we care about here.

get the dev build for Compose 1.7.0:

# cd /usr/local/bin
# wget -q https://dl.bintray.com/docker-compose/master/docker-compose-Linux-x86_64
# chmod 755 docker-compose-Linux-x86_64
# mv docker-compose-Linux-x86_64 docker-compose$(./docker-compose-Linux-x86_64 --version | awk '{print "-"$3$5}' | sed -e 's/,/_/')
# mv docker-compose docker-compose$(./docker-compose --version | awk '{print "-"$3$5}' | sed -e 's/,/_/')
# ln -s docker-compose-1.7.0dev_85e2fb6 docker-compose
# ls
lrwxrwxrwx 1 root root      31 Mar 30 08:38 docker-compose -> docker-compose-1.7.0dev_85e2fb6
-rwxr-xr-x 1 root root 7929597 Mar 24 08:01 docker-compose-1.6.2_4d72027
-rwxr-xr-x 1 root root 7938771 Mar 29 09:14 docker-compose-1.7.0dev_85e2fb6
#

In this case I decided to keep the 1.6.2 docker-compose binary along with the 1.7.0 docker-compose binary, then create a symlink to the one I wanted to use as the active docker-compose

Here’s a sample of how you might define a static IP address in docker-compose.yml that would work using docker-compose 1.7.0

version: "2"
services:
  host1:
    networks:
      mynet:
        ipv4_address: 172.25.0.101
networks:
  mynet:
    driver: bridge
    ipam:
      config:
      - subnet: 172.25.0.0/24