What are RESTful APIs and how do they facilitate communication in distributed systems?

Imagine your smartphone app fetching the latest news or an online game updating scores in real-time. How do different systems make these things happen? The answer often lies in RESTful APIs. A RESTful API (REST stands for Representational State Transfer) is a simple yet powerful way for software applications to communicate over the internet. In this beginner-friendly guide, we'll explain what RESTful APIs are and how they enable different parts of a distributed system to talk to each other. We'll also touch on real-world examples and why understanding RESTful APIs is valuable for system design interviews.

What Is a RESTful API?

A RESTful API is a set of rules for how different programs communicate over the web. REST stands for Representational State Transfer. In simple terms, a RESTful API uses standard HTTP requests (the same kind your browser uses) to let a client (like a web or mobile app) ask a server for data or actions and get a response back.

Key characteristics of RESTful APIs include:

• Standard web protocols: RESTful APIs rely on HTTP methods (GET, POST, PUT, DELETE) and resource URLs (e.g. /users/123). Any client able to make HTTP requests can use the API, and responses usually come in a lightweight format like JSON.
• Stateless communication: Each request stands on its own; the server keeps no memory of previous requests. This makes it easier to scale, because any server can handle any request without requiring shared session data.

In short, a RESTful API acts like a shared language, letting different software components exchange data smoothly. (For more fundamentals, see our What is RESTful API guide.)

How RESTful APIs Facilitate Communication in Distributed Systems

Distributed systems are applications made up of multiple components (services or servers) spread across different machines or networks. For example, an application might have separate services for accounts, product catalog, and orders, each running on different servers. These pieces need to exchange data and coordinate actions – that's where RESTful APIs come in.

RESTful APIs act as the communication glue in distributed systems. Each service can expose a RESTful API endpoint, and other services or client applications can call those endpoints over HTTP. This brings several benefits in a distributed architecture:

• Standard interface: All communication uses HTTP, so every service shares a common language. For instance, a service written in Java can talk to one written in Python as long as they use RESTful requests and responses.
• Loose coupling: One service only needs to know what API to call on another, not how the other service works internally. This means you can update or replace one service without breaking others, as long as the API contract stays the same.
• Scalability: Stateless APIs make scaling easier. Since each request is independent, any available server instance can handle it. If traffic grows, you can add more server instances behind a load balancer – each one can handle requests without relying on past history.

For example, one microservice can call another microservice's REST API to retrieve information. An Orders service might request stock data from an Inventory service by sending a GET request to an endpoint like /inventory/item/123. The Inventory service returns the data (e.g. in JSON), and the Orders service uses it to process the order.

RESTful APIs are now a standard way to facilitate data exchange between different applications. They’re commonly used to connect components in modern microservices architectures. Using RESTful APIs ensures even complex systems have a simple, reliable communication layer.

RESTful APIs in System Design Interviews

If you're preparing for a system design interview (or doing general software interview prep), expect RESTful APIs to come up. Interviewers often ask how the different services in your design will communicate. Proposing RESTful API calls is usually a well-understood answer.

During practice (e.g. mock interviews), be ready to explain why you'd use a RESTful service. For example, if asked how Service A gets data from Service B, you might answer, "Through a RESTful API over HTTP," then briefly mention benefits like language-agnostic communication and easier scaling due to statelessness. Also, know basic REST principles (like statelessness) in case the interviewer digs deeper into details.

For more interview-focused insights, check out our Q&A on Understanding RESTful APIs for Interviews and our guide on How to understand RESTful services for software interviews.

FAQs

Q1. What is a RESTful API in simple terms? It's a method for two programs to communicate over the web. One application sends requests to another using standard URLs and HTTP methods, and the server responds with the requested data (often in a format like JSON).

Q2. How do RESTful APIs work in a distributed system? In a distributed system (parts of an app on different servers), RESTful APIs allow those parts to communicate via HTTP. One service exposes an API endpoint (a URL) and another service sends a request to it. The server's response provides the needed information for them to work together.

Q3. Are RESTful APIs stateless, and why does that matter? Yes. RESTful APIs are designed to be stateless, meaning each client request stands on its own with all necessary data. The server doesn't store anything from previous requests. Statelessness makes it easier to scale because any server can handle any request without needing to know what happened before.

Key Takeaways

• RESTful API = Communication Backbone: A RESTful API provides a standardized way for different software components to communicate over HTTP.
• Ideal for Distributed Systems: Because they're stateless and language-agnostic, RESTful APIs enable services in a distributed system to work together smoothly (for example, in microservices or any multi-component app).
• Crucial for Interviews: Understanding RESTful APIs and how they fit into system architecture is essential for system design interview success.

Ready to deepen your system design skills? Explore Grokking System Design Fundamentals and Grokking the System Design Interview courses on DesignGurus.io to learn more and get hands-on practice for your next interview.