ROS 2 Services

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ros-2-services
Last updated: 
June 29, 2025

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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