ROS2 Communication Programming in Practice: Topics, Services, Actions, and QoS Usage

The article systematically explains how to write and choose between the three ROS2 inter-node communication methods—topics, services, and actions—and provides example code in C++ and Python for publishers, subscribers, service servers, and action servers. It focuses on three QoS parameters: depth, reliability, and history policy, and points out that when publisher and subscriber reliability settings are incompatible, QoS silently degrades, dropping data without reporting an error. Finally, it lists common problems such as topic type mismatches, request queuing caused by time-consuming service callbacks, and unfilled message timestamps, along with troubleshooting commands.