Ros2 Engineering Skills

ROS 2 Engineering Skills

A progressive-disclosure skill for ROS 2 development — from first workspace to production fleet deployment. Each section below gives you the essential decision framework; detailed patterns, code templates, and anti-patterns live in the references/ directory. Read the relevant reference file before writing code.

How to use this skill

1. Identify what the user is building (see Decision Router below).
2. Read the matching references/*.md file for detailed guidance.
3. Apply the Core Engineering Principles in every piece of code you generate.
4. When multiple domains intersect (e.g. Nav2 + ros2_control), read both files.

Decision router

When a task spans multiple domains, read all relevant files and reconcile conflicting recommendations by favoring safety, then determinism, then simplicity.

Cross-cutting concern — Security: Security is not isolated to references/security.md. Every domain should consider its security implications: hardware interfaces need safe shutdown on auth failure, DDS topics may need encryption, deployment images need supply chain verification, and fleet communication must use TLS. When reviewing code in any domain, check whether the data path crosses a trust boundary.

Core engineering principles

These apply to every ROS 2 artifact you produce, regardless of domain.

1. Distro awareness

Always ask which ROS 2 distribution the user targets. Key differences:

When the user does not specify, default to the latest LTS (Jazzy). Pin the exact distro in Dockerfile, CI, and documentation so builds are reproducible.

2. C++ vs Python decision

Choose the language based on the node's role, not personal preference.

Use rclcpp (C++) when:

• The node sits in a control loop running ≥100 Hz
• Deterministic memory allocation matters (real-time path)
• The node is a hardware driver or controller plugin
• Intra-process zero-copy communication is required

Use rclpy (Python) when:

• The node is orchestration, monitoring, or parameter management
• Rapid prototyping with frequent iteration
• Heavy use of ML frameworks (PyTorch, TensorFlow) that are Python-native
• The node does not sit in a latency-critical path

Mixed stacks are normal. A typical robot has C++ drivers/controllers and Python orchestration/monitoring. Note: component_container (composition) only loads C++ components via pluginlib. Python nodes run as separate processes, but can share a launch file and communicate via zero-overhead intra-host DDS.

Intra-process communication works for any nodes sharing a process — not only composable components. Any nodes instantiated in the same process with use_intra_process_comms(true) can use zero-copy transfer.

3. Package structure conventions

Every package should follow this layout. Consistency across a workspace reduces onboarding time and makes CI scripts portable.

my_package/
├── CMakeLists.txt          # or setup.py for pure Python
├── package.xml             # format 3, with <depend> tags
├── config/
│   └── params.yaml         # default parameters
├── launch/
│   └── bringup.launch.py   # Python launch file
├── include/my_package/     # C++ public headers (if library)
├── src/                    # C++ source files
├── my_package/             # Python modules (if ament_python or mixed)
├── test/                   # gtest, pytest, launch_testing
├── urdf/                   # URDF/xacro (if applicable)
├── msg/ srv/ action/       # custom interfaces (dedicated _interfaces package preferred)
└── README.md

Separate interface definitions into a *_interfaces package so downstream packages can depend on interfaces without pulling in implementation.

4. Parameter discipline

• Declare every parameter with a type, description, range, and default in the node constructor — never use undeclared parameters.
• Use ParameterDescriptor with FloatingPointRange or IntegerRange for numeric bounds. The parameter server rejects out-of-range values at set time.
• Group related parameters under a namespace prefix: controller.kp, controller.ki, controller.kd.
• Load defaults from a config/params.yaml; allow launch-time overrides.
• For dynamic reconfiguration, register a set_parameters_callback and validate new values atomically before accepting.

5. Error handling philosophy

• Nodes must not silently swallow errors. Log at the appropriate severity, then take a safe action (stop motion, request help, transition to error state).
• Prefer lifecycle node error transitions over ad-hoc boolean flags.
• When calling a service, always handle the "service not available" and "future timed out" cases explicitly.
• For hardware drivers, distinguish transient errors (retry with backoff) from fatal errors (transition to FINALIZED and alert the operator).

6. Quality of Service defaults

Start from these profiles and adjust per use case:

QoS mismatches are the #1 cause of "I published but nobody receives." Always check compatibility with ros2 topic info -v when debugging.

DEADLINE and LIFESPAN are critical for safety-critical systems. DEADLINE fires an event when no message arrives within the specified period (detect stale data). LIFESPAN discards messages older than the specified duration before delivery (prevent acting on stale data). See references/communication.md section 9 for full API and examples.

7. Naming conventions