ros2-qos-dds

# ROS 2 QoS and DDS ## Compatibility (silent failure #1) | Publisher | Subscriber | OK? | |-----------|------------|-----| | RELIABLE | RELIABLE | yes | | RELIABLE | BEST_EFFORT | yes | | BEST_EFFORT | BEST_EFFORT | yes | | BEST_EFFORT | RELIABLE | **no** | Durability: `TRANSIENT_LOCAL` pub + `VOLATILE` sub → late joiners miss latch-like data. Map/static TF often need matching `TRANSIENT_LOCAL`. ## Profiles by intent - **Sensors** (camera, lidar): BEST_EFFORT, KEEP_LAST depth 1–5, VOLATILE (`SensorDataQoS`). - **Commands** (cmd_vel, goals): RELIABLE, KEEP_LAST ≥10, VOLATILE. - **Maps / latched config**: RELIABLE + TRANSIENT_LOCAL, depth 1. - Never rely on “default 10” for production — set QoS explicitly on both ends. ## Discovery / isolation ```bash export ROS_DOMAIN_ID=42 # 0–101; isolate fleets on one LAN export ROS_LOCALHOST_ONLY=1 # no off-host discovery export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp # or rmw_fastrtps_cpp ``` Same `ROS_DOMAIN_ID` + compatible RMW required across machines. Mixing RMW implementations is unsupported. ## Debug ```bash ros2 topic info /topic -v # Reliability / Durability / publishers / subscribers ros2 doctor ros2 daemon stop && ros2 daemon start ``` If `ros2 topic hz` works but your node sees nothing → almost always QoS mismatch. ## Large data - Prefer composition + intra-process (`UniquePtr` callbacks) for images/clouds in-process. - Raise DDS socket / message size (Cyclone `CYCLONEDDS_URI`) when samples exceed defaults. - Watch static arrays and nested msgs for sample-size blowups (see `ros2-interfaces`).