ROS 2 Core Concepts

From your first node to orchestrating full robotic systems with topics, services, actions, parameters, and launch files.
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ros-2-core-concepts
Last updated: 
June 29, 2025

ROS 2 is a modular robot framework where everything starts with a node — but that’s just the beginning. To build anything meaningful, you’ll also need to master topics, services, actions, parameters, and launch files. This guide walks you through each of these in a hands-on, progressive flow.

🚀 ROS 2 Core Concepts Overview

ROS 2 is a flexible framework for building robot software. Its power lies in how it breaks a system into small, reusable components that communicate cleanly. These components — called nodes — talk to each other using well-defined mechanisms: topics, services, and actions. Developers can configure behavior at runtime using parameters, and orchestrate entire systems with launch files.

🧩 Node

A node is a single unit of work in ROS 2—like a sensor driver, motion planner, or controller. Each node runs independently but can communicate with others.

📡 Topic

Topics are used for one-way, streaming communication. A node publishes messages on a topic (e.g., camera frames), and other nodes subscribe to receive that data.

🔄 Service

Services provide synchronous, two-way communication. One node sends a request and waits for a response—perfect for tasks like spawning a new robot or querying a sensor.

🏹 Action

Actions are for longer tasks where you want feedback during execution (e.g., moving to a goal). They let a client monitor progress and cancel if needed.

⚙️ Parameter

Parameters are dynamic settings you can use to change how a node behaves—like setting speed limits, thresholds, or visual styles—without modifying code.

🚀 Launch File

A launch file bundles all your startup logic: which nodes to run, with which parameters, in what sequence. It’s the backbone of reproducible deployments.

🔗 Want to dive deeper?
Click on any concept below to explore how it works, when to use it, and real examples:

  • Nodes – What they are and how they structure your robot
  • Topics – Stream data between nodes efficiently
  • Services – Ask and receive information on demand
  • Actions – Send long-running goals with live feedback
  • Parameters – Tune your robot without changing code
  • Launch Files – Start your whole system with one command

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