Diagnose Topic and Communication Failures

Assume both nodes are alive but messages do not arrive.

Now move to communication evidence.

Step 1: exact topic names/types

ros2 topic list -t

Step 2: endpoint evidence

ros2 topic info <topic_name> --verbose

Ask:

• publisher count?
• subscription count?
• endpoint node names?
• same topic type?

Step 3: message evidence

ros2 topic echo <topic_name>

Step 4: interface contract

ros2 interface show <message_type>

Controlled failure

Temporarily change the listener source or launch remap so it uses a different topic name. Build/source as required and observe:

both nodes alive
but
publisher/subscriber no longer share one resolved topic

Repair it and collect the same endpoint evidence.

Checkpoint

Write the shortest command sequence that proves a naming/remapping mismatch without opening either Python source file first.