ROS2 galactic nodes can't communicate through docker container border

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This question is a direct follow up to this one: ROS2-foxy nodes can't communicate through docker container border

Recap in Foxy:

The following does not work

docker run -it --net=host --rm osrf/ros:foxy-desktop ros2 run demo_nodes_cpp talker

In Terminal 2:

docker run -it --net=host --rm osrf/ros:foxy-desktop ros2 run demo_nodes_cpp listener

The resolution was to mount the shared memory into both containers, because of how Fast-DDS works when it believes it's on the same machine:

In terminal 1:

docker run -it --net=host -v /dev/shm:/dev/shm --rm osrf/ros:foxy-desktop ros2 run demo_nodes_cpp talker

In terminal 2:

docker run -it --net=host -v /dev/shm:/dev/shm --rm osrf/ros:foxy-desktop ros2 run demo_nodes_cpp listener

Now back to ROS2 Galactic. AFAIK ROS2 Galactic uses Cyclone DDS, so the shared memory solution does not work anymore.

So what do i have to do to get the following to work?

In Terminal 1:

docker run -it --net=host --rm osrf/ros:galactic-desktop ros2 run demo_nodes_cpp talker

In Terminal 2:

docker run -it --net=host --rm osrf/ros:galactic-desktop ros2 run demo_nodes_cpp listener