How to get the IP address of the docker host from inside a docker container

Question

As the title says. I need to be able to retrieve the IP address the docker hosts and the portmaps from the host to the container, and doing that inside of the container.

Answer 1

AFAIK, in the case of Docker for Linux (standard distribution), the IP address of the host will always be 172.17.0.1 (on the main network of docker, see comments to learn more).

The easiest way to get it is via ifconfig (interface docker0) from the host:

ifconfig

From inside a docker, the following command from a docker: ip -4 route show default | cut -d" " -f3

You can run it quickly in a docker with the following command line:

# 1. Run an ubuntu docker
# 2. Updates dependencies (quietly)
# 3. Install ip package   (quietly)
# 4. Shows (nicely) the ip of the host
# 5. Removes the docker (thanks to `--rm` arg)
docker run -it --rm ubuntu:19.10 bash -c "apt-get update && apt-get install iproute2 -y && ip -4 route show default | cut -d' ' -f3"