ROS2 DDS Discovery - Participant Filtering

Problem Statement

In ROS2, nodes discover each other automatically via DDS (Data Distribution Service). This discovery is scoped by the ROS_DOMAIN_ID — nodes in different domains are completely invisible to each other. This is how you isolate a robot fleet, a test environment, or a secure subsystem.

Requirements

• Create a node named secure_node
• Declare a parameter domain_id with a default value of 0
• Read the ROS_DOMAIN_ID environment variable using os.environ.get("ROS_DOMAIN_ID", "0")
• On startup, log exactly: "Operating in Domain ID: X" where X is the domain ID value
• Also log: "Participant filtering active: secure_node is isolated to this domain"

Input/Output Format

Output (console logs on startup):

[secure_node]: Operating in Domain ID: 42
[secure_node]: Participant filtering active: secure_node is isolated to this domain

How Domain ID Works

Robot A (DOMAIN_ID=0) ←—cannot see—→ Robot B (DOMAIN_ID=1)
Robot A (DOMAIN_ID=0) ←—can see——→  Robot C (DOMAIN_ID=0)

Setting different domain IDs is the simplest way to run multiple independent ROS2 systems on the same network without interference.

⚠️ Common Pitfalls

• os.environ.get("ROS_DOMAIN_ID", "0") returns a string — don't forget int() if you need to compare numerically
• Forgetting import os at the top of your file
• Domain ID must be an integer between 0 and 101 (ROS2 Humble restriction)

📚 Helpful Resources

• ROS2 Domain ID Concepts
• ROS2 DDS Tuning