Unlocking System Design: WebSockets vs. REST API Explained

WebSockets and REST APIs are two communication protocols that serve different purposes in system design. Choosing between them—or deciding how to use them together—depends on the specific requirements of your application. Here’s a comparison and an overview of how to integrate them into a system’s design:

REST API (Representational State Transfer)

• Think of a REST API like sending letters. Every time you want to communicate with someone, you write a letter, put it in the mailbox, and wait for them to reply. If you want to talk to them again, you have to write another letter and send it.

• Nature: REST APIs are stateless, request-response-based protocols typically used over HTTP.
• Use Case: Best for CRUD (Create, Read, Update, Delete) operations, where the client requests data and the server respond. REST is ideal for applications that need a straightforward, resource-oriented communication pattern.
• Scalability: Highly scalable due to its stateless nature, making it easier to manage load balancing and caching.
• Data Format: Supports data formats like JSON, XML, and others, but JSON is the most common.
• Advantages:
  • Easy to understand and implement.
  • Works well for most scenarios that do not require real-time communication.
  • Highly compatible with HTTP and easily integrates with existing web infrastructure.
• Limitations:
  • Not ideal for real-time updates as it requires continuous polling or frequent client-server requests.
  • Higher latency compared to real-time solutions because each interaction needs a new HTTP request.

WebSockets

• Imagine you’re having a phone call with a friend. You both can talk and listen to each other without hanging up. There’s an ongoing conversation where either of you can speak at any time without waiting for the other to ask first.

• Nature: WebSockets provide a full-duplex communication channel that allows persistent connections between the client and server.
• Use Case: Perfect for real-time applications like chat systems, live notifications, stock market updates, or multiplayer games where data exchange needs to be instantaneous and continuous.
• Scalability: Requires stateful connections, which can be more complex to scale compared to REST. However, frameworks and platforms like Redis Pub/Sub, message brokers, or WebSocket load balancers can help handle this complexity.
• Data Format: Typically transmits JSON or other lightweight data formats over a TCP-based connection.
• Advantages:
  • Low latency communication, as it keeps the connection open.
  • Efficient for use cases that involve real-time data and continuous interaction.
  • Reduces overhead as it does not require the repeated opening and closing of HTTP connections.
• Limitations:
  • More complex to implement and manage, especially when scaling the system.
  • Requires WebSocket-capable infrastructure, which might be more demanding than standard HTTP/REST services.

System Design Integration

In modern system design, it is common to use both REST APIs and WebSockets in a complementary manner. Here are some strategies on how to integrate them effectively:

• REST for Resource Management, WebSockets for Real-Time Updates: Use REST APIs for operations that involve data retrieval or updates (CRUD operations), such as fetching a list of items or submitting a form. Use WebSockets for pushing real-time updates to the client when data changes, such as live notifications or data streams.
• Fallback Mechanism: WebSockets can have a fallback mechanism to REST-based polling if the WebSocket connection fails or is not supported by the client. This approach ensures that the client can still get updates even if real-time capabilities are unavailable.
• Hybrid Models: Some applications may start with REST API calls to establish initial data and then open a WebSocket connection to receive subsequent changes. This approach minimizes latency while leveraging the strengths of both protocols.

Choosing Between WebSockets and REST

The decision depends on factors like:

• Real-Time Requirements: WebSockets are necessary when real-time communication is a critical feature (e.g., chat apps, gaming).
• Network Overhead: If minimizing the frequency of requests is important, WebSockets are more efficient because they maintain an open connection.
• Complexity and Scalability: REST is simpler to implement and manage, especially when scaling horizontally.
• Compatibility and Infrastructure: REST is more universally supported, as it works seamlessly with existing HTTP infrastructure.

Best Practices

• Security: Use authentication mechanisms like OAuth or JWT for both REST and WebSockets to secure the connection.
• Load Balancing: For WebSockets, consider using a reverse proxy or load balancer capable of handling WebSocket traffic (e.g., Nginx or HAProxy).
• Error Handling: Implement robust error handling and reconnection logic for WebSockets, as network issues may cause disconnections.

case studies

Slack – Real-Time Messaging and Communication

• Technology Stack: WebSockets
• Use Case: Slack uses WebSockets to provide real-time messaging and notifications to users. The WebSocket connection allows messages to be pushed instantly to all connected clients as soon as they are sent, without the need for the client to continuously poll the server.
• Approach: While WebSockets handle the real-time communication, Slack also uses REST APIs for initial data retrieval, such as loading a list of channels or fetching user details when a user logs in.
• Benefits: This approach ensures efficient use of server resources and low-latency communication, which is crucial for collaboration and instant messaging.

Uber – Efficient Data Communication

• Technology Stack: WebSockets and REST APIs
• Use Case: Uber’s system relies on a combination of REST APIs and WebSockets to deliver a seamless user experience. When a user requests a ride, REST APIs handle the data retrieval and submission, like fetching nearby drivers, user profiles, and ride pricing.
• Real-Time Updates: Once a ride is booked, WebSockets come into play to provide real-time updates about the ride’s status, driver location, and estimated arrival time. This prevents the need for constant polling, which would otherwise cause unnecessary overhead.
• Scalability: Using WebSockets for live updates allows Uber to scale efficiently, as the communication is persistent and requires fewer resources compared to repeatedly creating and closing HTTP requests.

Combining both REST and WebSockets can offer a flexible and robust communication setup, catering to a broad range of system design needs.