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ROS 2 Services
In robotics, sometimes a robot needs to ask before it acts.
That’s where ROS 2 services come in — they enable request/response interactions between nodes. Unlike topics, which stream data continuously, services are used when you want something more structured and deliberate: “Hey, can you reset the counter?” or “Should I turn on this LED?”
Whether you’re toggling a sensor, resetting a simulation state, or commanding a one-time action, services give your robot a synchronous way to make decisions.
🔧 Understanding ROS 2 Services: Deterministic Request/Response in Robotic Systems
In ROS 2, services provide a synchronous communication mechanism between nodes — ideal for tasks that require explicit invocation and guaranteed response handling. Unlike topics, which implement a pub/sub model for continuous data streams, services follow a strict client/server paradigm where a node sends a request and blocks until it receives a response.
This design makes services a critical tool for:
- Managing robot state transitions (e.g., initializing or resetting components)
- Performing gated actions (e.g., actuating hardware after validation)
- Controlling deterministic behavior in test automation or safety routines
In high-fidelity simulation environments like Isaac Sim, services are particularly valuable for synchronizing simulation control with ROS-based test logic — allowing you to programmatically reset scenes, inject dynamic events, or toggle components with surgical precision.
🛠️ How Services Work
A ROS 2 service consists of:
- A name (e.g.
/reset_counter) - A request (e.g.
{int: 0}) - A response (e.g.
{success: true})
One node runs a service server that waits for requests. Another node runs a service client that sends them.
You can define your own .srv files with custom request and response types — or reuse common ones like SetBool or Trigger.
🧪 Common Use Cases
- Resetting a simulation
- Calibrating sensors
- Activating a robot component
- Triggering a one-time behavior
Services are perfect when you want to:
- Control what happens and when
- Get an acknowledgment
- Avoid the constant chatter of topics
🌐 Bonus: Pair with USD
You can embed custom USD prims and metadata that respond to ROS 2 service calls. This creates a reproducible loop: bag replay → ROS service → USD state change → test results → bag record.
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