Add per node & component log level support

[penww]

Description

This issue tracks the addition of a log_level field to NodeOptions, allowing users to set the initial log severity for a node at construction time. This enables per-component log level customization, particularly useful in component container deployments.

Motivation

In ROS 2, all nodes loaded into a component container share the same process. Prior to this change, there was no way to specify a different initial log level for individual components at load time — the only option was to set a global log level or call set_level() programmatically after construction.

This is a common need in production deployments where:

• Different components have different verbosity requirements (e.g., a sensor driver at WARN, a planner at DEBUG).
• Operators want to configure log levels declaratively via launch files or LoadNode service calls without modifying node source code.
• Debugging a single component in a multi-component container should not require restarting the entire process with a global log level change.

We can see this feature has designed but not full implementation:

• LoadNode.srv defined log_level field: https://github.com/ros2/rcl_interfaces/blob/79a773f9fb02dee0de23fb1b08ca4d187b313849/composition_interfaces/srv/LoadNode.srv#L17
• ros2component implement log_level args but not parse: https://github.com/ros2/ros2cli/blob/401876461924b6bd4d4f9db95e22deb6243fce8b/ros2component/ros2component/api/__init__.py#L343
• component_manager not handle log_level in the LoadNode request:

  rclcpp/rclcpp_components/src/component_manager.cpp

  Line 150 in f145c9e

  ComponentManager::create_node_options(const std::shared_ptr<LoadNode::Request> request)

Expected Behavior:

• Set component log_level with CLI:

ros2 component load /ComponentManager <PKG> <PLUGIN> --log-level debug

• Set component log_level with launch:

def generate_launch_description():
    return LaunchDescription([ComposableNodeContainer(
        name='component_demo_container',
        namespace='',
        package='rclcpp_components',
        executable='component_container',
        composable_node_descriptions=[
            ComposableNode(
                package='<PKG>',
                plugin='<PLUGIN>',
                log_level='DEBUG',  # component log level
            ),
        ],
        arguments=['--ros-args', '--log-level', 'DEBUG'],  # container log level
    )])

Design / Implementation Considerations

NodeOptions API

A new log_level getter/setter pair is added to NodeOptions:

// Get the log level (RCUTILS_LOG_SEVERITY_* value; 0 = unset/default)
int log_level() const;

// Set the initial log level for this node
NodeOptions & log_level(int log_level);

The default value is RCUTILS_LOG_SEVERITY_UNSET (0), which preserves existing behavior — no level is applied at construction.

Node construction (node.cpp)

After the node is fully constructed, if log_level is not UNSET, the logger level is applied:

if (options.log_level() != RCUTILS_LOG_SEVERITY_UNSET) {
  node_logging_->get_logger().set_level(
    static_cast<rclcpp::Logger::Level>(options.log_level()));
}

This is intentionally applied after construction so the logger is fully initialized.

ComponentManager integration (component_manager.cpp)

When handling a LoadNode service request, the log_level field from the request is validated and forwarded to NodeOptions:

if (request->log_level != 0) {
  // Validate against known RCUTILS severity values
  options.log_level(request->log_level);
}

Invalid values (not one of DEBUG, INFO, WARN, ERROR, FATAL) throw a ComponentManagerException with a descriptive message.

Additional Information

No response