You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. If you want up-to-date information, please have a look at Galactic.

Running 2 nodes in 2 separate docker containers [community-contributed]

Open a terminal. Run the image in a container in interactive mode and launch a topic publisher (executable talker from the package demo_nodes_cpp) with ros2 run:

docker run -it --rm osrf/ros:dashing-desktop ros2 run demo_nodes_cpp talker

Open a second terminal. Run the image in a container in interactive mode and launch a topic subscriber (executable listener from the package demo_nodes_cpp) with ros2 run:

docker run -it --rm osrf/ros:dashing-desktop ros2 run demo_nodes_cpp listener

As an alternative to the command line invocation, you can create a docker-compose.yml file (here version 2) with the following (minimal) content:

version: '2'

services:
  talker:
    image: osrf/ros:dashing-desktop
    command: ros2 run demo_nodes_cpp talker
  listener:
    image: osrf/ros:dashing-desktop
    command: ros2 run demo_nodes_cpp listener
    depends_on:
      - talker

To run the containers call docker-compose up in the same directory. You can close the containers with Ctrl+C.