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Set up the ROS_DOMAIN_ID in ROS 2#
The PAL OS Docker image and robots of PAL use the ROS_DOMAIN_ID in combination with a custom
Cyclone DDS configuration in order to establish P2P connection between ROS 2
systems. This allows for a more stable way of connecting to different ROS 2 systems
and is more network friendly when using multiple ROS 2 systems on the same network.
Steps on how to establish a connection between a PAL OS Docker image and a robot can be found
in Set up ROS 2 communication with the robot.
The ROS_DOMAIN_ID is an environment variable in ROS 2 that is used to separate
multiple ROS 2 processes running on the same network. Nodes with the same ROS_DOMAIN_ID
can communicate with each other, but are not able to communicate to nodes with a
different ROS_DOMAIN_ID. By setting different ROS_DOMAIN_ID values, you can run
multiple ROS 2 processes on the same network without interference between them. A more
detailed explanation of the ROS_DOMAIN_ID can be found in the
ROS 2 documentation.
Important
By using the custom Cyclone DDS configuration, topics are not accessible from outside even
with the same ROS_DOMAIN_ID set, unless you explicitly connect to the robot with
the connection script. Section Set up ROS 2 communication with the robot explains how to use the
connection script.
To show the ROS_DOMAIN_ID of the robot, the following command can be used inside the robot:
echo $ROS_DOMAIN_ID
in the PAL OS Docker image the ROS_DOMAIN_ID is set to 0 by default. To be able to establish P2P
connection with the robot, change the ROS_DOMAIN_ID in your PAL OS Docker image to the same
ROS_DOMAIN_ID as the robot. This can be done with the following commands:
# Set the same ROS_DOMAIN_ID as the robot
export ROS_DOMAIN_ID=42
# Show the current ROS_DOMAIN_ID
echo $ROS_DOMAIN_ID
# Make the ROS_DOMAIN_ID persistent
echo "export ROS_DOMAIN_ID=42" >> ~/.bashrc
Note
Changes to a Docker image can also be saved by committing the changes to a new image.
See the Docker tutorials to learn more about Docker.