What is Rate Limiting?

Rate limiting is a technique to control the rate of access to APIs. It enforces a limit on the number of API calls that a client can make within a specific time period. This helps protect the API from excessive usage, whether it is accidental or intentional. Rate limiting is a key technique in managing and protecting APIs, it helps to prevent overuse, defend against DDoS attacks, enforce fair usage, improve scalability, and facilitate billing.

Rate Limiting Algorithms

There are several algorithms that can be used to implement rate limiting, including:

1. Token Bucket: This algorithm works by allowing a certain number of requests (tokens) to be made within a specific time period. When a request is made, a token is removed from the bucket. If the bucket is empty, the request is denied.

2. Leaky Bucket: This algorithm is similar to the token bucket, but instead of denying requests when the bucket is empty, it allows the requests to be made, but at a slower rate.

3. Fixed Window: This algorithm keeps track of the number of requests made within a fixed time window. If the number of requests exceeds a certain threshold, further requests are denied.

4. Sliding Window: This algorithm is similar to the fixed window, but instead of a fixed time window, the window slides with each request.

5. Rolling Window: This algorithm tracks the number of requests over a rolling time period, such as the last minute, hour, or day.

Implementation Strategies in Spring Boot App

1. Using the Spring Boot Actuator: The Actuator module in Spring Boot provides a set of endpoints for monitoring and managing the application. It includes a built-in rate limiter that can be used to limit the number of requests to specific endpoints.

2. Using Spring Cloud Gateway: Spring Cloud Gateway is a library that can be used to build and configure API gateways. It includes a rate limiter filter that can be used to limit the number of requests to specific routes.

3. Using a Third-Party Library: There are several third-party libraries available for rate limiting in Spring Boot, such as the Spring AOP based ratelimiter and the Guava RateLimiter.

4. Using a Custom Filter: You can also implement a custom filter in Spring Boot to rate limit requests. This would involve creating a filter that intercepts incoming requests, checks against a rate limit, and either allows or denies the request based on the limit.

How to Implement Rate Limiter using Guava Library

Step 1: Add the Guava library to your project’s dependencies:

<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>29.0-jre</version>
</dependency>

Step 2: Create a class for the rate limiter and instantiate a RateLimiter object

import com.google.common.util.concurrent.RateLimiter;

@Component
public class MyCustomRateLimiter {
private final RateLimiter rateLimiter = RateLimiter.create(10); // Limit to 10requests per second
}

Step 3: Inject the rate limiter into your controller or service classes and use it to limit the number of requests

@RestController
public class MyRestController {
private final MyCustomRateLimiter myRateLimiter;

public MyRestController(MyCustomRateLimiter myRateLimiter) {
this.myRateLimiter = myRateLimiter;
}

@GetMapping("/api/resource")
public ResponseEntity getResource() {
if (!myRateLimiter.rateLimiter.tryAcquire()) {
return ResponseEntity.status(HttpStatus.TOO_MANY_REQUESTS).body("Too many requests, please try again later.");
}

// Your business logic code to handle the request
}
}

This is a simple example of how to use Guava RateLimiter in a Spring Boot application. You can further customize the rate limiter to suit your needs. Overall, Guava RateLimiter is a powerful library that can be used in a variety of use cases when building Spring Boot applications. It is particularly useful when you need more control over rate limiting and more flexibility than the built-in rate limiter in Spring Boot Actuator.

Practical ways to implement rate limiters.

1. Using an API Gateway built-in feature: Some API gateways, such as Kong, AWS API Gateway, and Azure API Management, provide built-in rate-limiting features that can be easily configured. These features can be used to limit the number of requests to specific endpoints, specific users or IPs, or specific resources.

2. Using a plugin or middleware: Some API gateways, such as Nginx or Tyk, provide plugins or middleware that can be used to implement rate limiting. These plugins or middleware can be configured to limit the number of requests to specific endpoints, specific users or IPs, or specific resources.