Ros2 Knowledge Patch

ROS 2 Knowledge Patch

Use this skill when selecting ROS 2 platforms or middleware, updating build configuration, writing rclcpp or rclpy code, operating Rosbag2, or working with interfaces and launch substitutions. Check migration hazards first, then open the topic reference that matches the task.

Reference Index

Migration Hazards

Replace ament_target_dependencies()

ament_target_dependencies() is deprecated. Link imported modern CMake targets directly:

target_link_libraries(my_target PUBLIC SomePackage::SomeTarget)

Do not mix the plain and keyword signatures for one target. If an existing target_link_libraries() call uses the plain form, leave out PUBLIC, PRIVATE, and INTERFACE in later calls for that target.

Update Fast DDS profile configuration names

The underlying fastrtps name is now fastdds. RMW implementation names do not change, but environment-variable names used for XML profiles do. Audit scripts, CI variables, and launch environments that configure Fast DDS rather than renaming the selected RMW implementation.

Stop planning new work around Connext Micro

rmw_connextddsmicro is deprecated and receives no further Kilted updates. Choose a supported RMW implementation for maintained deployments.

Remove float128 from dynamic typesupport paths

rosidl_dynamic_typesupport no longer supports float128. Change dynamic type descriptions and consumers to a supported numeric representation before upgrading.

Expect one bag per snapshot trigger

Snapshot recording no longer reuses the same output bag. Every trigger writes a new bag file. Automation that discovers, uploads, rotates, or counts snapshot outputs must handle multiple files.

Preserve subordinate-node semantics

Generic clients created from an rclcpp subordinate node now honor its sub-namespace. Parameter access through that node uses the parent node's rclcpp::node_interfaces::NodeParametersInterface. Recheck resolved client names and parameter behavior if older code depended on the previous behavior.

Platform and Middleware Selection

Use the detailed compatibility tables before choosing an operating system, architecture, compiler, or RMW implementation. Important constraints include:

• Ubuntu 24.04 on amd64 and arm64, and Windows 10 with Visual Studio 2019 on amd64, are Tier 1 targets.
• RHEL 9 on amd64 is Tier 2.
• Debian 12 and macOS on amd64 are Tier 3.
• The minimum language levels are C++17 and Python 3.9.
• Ionic is the recommended Gazebo release.

rmw_fastrtps_cpp remains the default RMW implementation and uses Fast DDS 2.14.4. Fast DDS, Cyclone DDS 0.10.5, Connext DDS 7.3, and Zenoh 1.0.4 are Tier 1 middleware implementations. Connext excludes arm64 and is limited to Ubuntu, Windows, and macOS. rmw_zenoh_cpp is newly Tier 1.

See Compatibility, middleware, and builds for the full matrices and build guidance.

Rosbag2 Quick Reference

Merge bags during playback

Repeat -i or --input to merge multiple bags into one playback:

ros2 bag play -i bag1 -i bag2 -i bag3

Choose timestamp ordering

Publication-time order is opt-in:

ros2 bag play <bag> --message-order sent

sent orders by publication timestamp. The default, received, orders by reception timestamp.

Sort and size bag contents

ros2 bag info --sort sorts topics, services, and actions by name, type, or recorded-message count. In verbose output, add --size-contribution to report each topic's share of the bag size:

ros2 bag info -v --sort <criterion> --size-contribution <bag>

Set Rosbag2 log verbosity

Both playback and recording accept --log-level:

ros2 bag play <bag> --log-level debug
ros2 bag record <topics...> --log-level debug

Action Introspection

Inspect a running action from the CLI:

ros2 action echo <action_name>

Rosbag2 can record and replay action data. rclcpp also provides the generic action client support underlying generic action tooling. See Rosbag2 and actions before building generic action inspection or replay workflows.

Python Typing Quick Reference

rclpy publishers, subscriptions, services, actions, tasks, futures, and parameters support generic type annotations. Clients carry request and response types; action clients carry goal, result, and feedback types:

client: Client[GetParameters.Request, GetParameters.Response]
action: ActionClient[Fibonacci.Goal, Fibonacci.Result, Fibonacci.Feedback]
future: Future[bool] = Future()

Use these parameters in application annotations and reusable APIs instead of erasing the ROS interface types. See Client libraries and execution for executor and node-behavior changes that commonly accompany client-library updates.

Launch Path Composition

PathJoinSubstitution accepts a list of strings or substitutions as one path component. Use a nested list when a filename combines a substituted basename and a literal suffix:

PathJoinSubstitution([
    'robot_description', 'urdf',
    [LaunchConfiguration('model'), '.xacro'],
])

This avoids a separate concatenation helper. More interface and encoding changes are in Interfaces and launch.

New Capability Checklist

When the task touches these areas, account for the corresponding capability:

• Use rmw_test_fixture and its provider implementation package for RMW-specific communication isolation in tests.
• Consider the experimental Python EventsExecutor when evaluating an event-driven executor, but keep its experimental status explicit.
• Use nav_msgs/msg/Goals when a message needs an array of navigation goals.
• Permit NV12 in common-interface image encoding paths, especially for hardware-decoder output.
• Expect Rust interfaces to be generated by default because rosidl_rust is in the default generator set.
• Consider DDS topic instances when multiple logical objects should publish updates on one topic.

Review Checklist

Before finalizing ROS 2 changes:

1. Verify the target platform tier, architecture, compiler, and language minimums.
2. Confirm the RMW implementation is supported on the selected platform and that Fast DDS configuration uses the renamed profile environment variables.
3. Replace deprecated CMake dependency calls without mixing CMake signature styles.
4. Remove unsupported dynamic float128 types and avoid new Connext Micro dependencies.
5. Recheck subordinate-node client names and parameter access.
6. Decide explicitly whether bag playback needs reception or publication ordering, and handle a new output bag for every snapshot trigger.
7. Apply concrete generic parameters to Python ROS entities where static typing is part of the task.
8. Treat the Python events executor as experimental in design and deployment decisions.