Ros2 Knowledge Patch

ROS 2 Compatibility Guide

Use this skill when writing, reviewing, migrating, or debugging ROS 2 code whose behavior depends on the covered distribution. Prefer the project's manifests, source, configuration, and tests when they show different behavior.

Reference index

Migration priorities

Replace ament_target_dependencies()

The helper is deprecated. Link imported modern CMake targets directly with target_link_libraries():

target_link_libraries(my_target PUBLIC SomePackage::SomeTarget)

Do not mix the keyword and plain signatures for one target. If an earlier call for that target is plain, leave PUBLIC, PRIVATE, and INTERFACE out of later calls too.

Update Fast DDS naming in configuration

The underlying middleware name changed from fastrtps to fastdds. ROS middleware implementation identifiers did not change, but XML-profile environment-variable names did. Audit environment configuration and deployment scripts even when the selected RMW implementation name remains valid.

Move away from Connext Micro

rmw_connextddsmicro is deprecated and receives no further updates for this distribution. Choose another supported RMW implementation for maintained deployments.

Remove dynamic float128 assumptions

rosidl_dynamic_typesupport no longer supports float128. Change schemas or dynamic-type handling that relies on it.

Build and platform quick reference

Use at least C++17 and Python 3.9. The recommended Gazebo release is Ionic.

Tier 1 targets are:

• Ubuntu 24.04 on amd64 and arm64.
• Windows 10 with Visual Studio 2019 on amd64.

RHEL 9 on amd64 is Tier 2. Debian 12 and macOS on amd64 are Tier 3. Treat these tiers as support expectations when selecting CI runners and deployment targets.

For Windows source work, provision dependencies with Pixi/Conda plus pip and isolate them per workspace instead of installing them globally.

Middleware quick reference

rmw_fastrtps_cpp remains the default and uses Fast DDS 2.14.4. Tier 1 middleware implementations include:

• Fast DDS.
• Cyclone DDS 0.10.5.
• Connext DDS 7.3.
• Zenoh 1.0.4 through the newly Tier 1 rmw_zenoh_cpp.

Connext does not support arm64 here and is limited to Ubuntu, Windows, and macOS. Check that constraint before selecting it for multi-architecture builds.

Use rmw_test_fixture to define communication isolation around an RMW test. The companion rmw_test_fixture_implementation package discovers, loads, and invokes the provider-specific implementation.

DDS topic instances are supported, so updates for multiple objects of one logical kind can share one topic.

Rosbag playback quick reference

Merge several bags during playback by repeating -i or --input:

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

Reception order remains the default. To order by publication timestamp, use:

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

Use --log-level with both playback and recording when command-level logging must be adjusted:

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

Every trigger in snapshot recording mode now creates a new bag file. Do not design workflows around a previous snapshot file being reused.

Rosbag inspection quick reference

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

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

Actions quick reference

The CLI can inspect action traffic directly:

ros2 action echo <action_name>

Rosbag2 can record and replay action data. rclcpp supplies the generic action client support used for action tooling and type-independent clients.

Python client typing

Publishers, subscriptions, services, actions, tasks, futures, and parameters support generic type annotations. Service clients take request and response types; action clients take 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 generics in annotations rather than falling back to unparameterized client and future types.

Executors and subordinate nodes

rclpy includes an experimental EventsExecutor, bringing the event-driven executor concept from rclcpp to Python. Keep the experimental status in mind when choosing it for long-lived APIs.

Generic clients created from an rclcpp subordinate node honor that node's sub-namespace. Parameter access through a subordinate node uses the parent node's rclcpp::node_interfaces::NodeParametersInterface.

Interfaces and generated code

nav_msgs/msg/Goals carries an array of navigation goals. Use it when an API needs a collection of goals rather than inventing a parallel message shape.

rosidl_rust is enabled among the default ROS interface code generators, so default interface generation includes Rust artifacts.

NV12 is a common-interface pixel encoding and can represent frames from hardware-accelerated decoders directly.

Launch path composition

PathJoinSubstitution accepts a list of strings or substitutions as one path component. This supports a substituted basename plus a suffix without a separate concatenation helper:

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

Use the nested list only for pieces that form one component; keep separate path components as separate outer-list entries.