Custom gateway filters in Spring Cloud Gateway

To implement custom gateway filters in Spring Cloud Gateway (SCG) for Debouncing, Throttling, Rate Limiting, Exponential Backoff, or other custom logic, you can define custom filters in your Spring Cloud Gateway project and configure them using the application.yml file.

1. Spring Cloud Gateway Overview

Spring Cloud Gateway provides a flexible way to create custom filters that can apply logic such as debouncing, throttling, and rate limiting at the gateway level. This can help protect downstream services and ensure efficient use of resources.

Steps to Create Custom Filters:

Add Spring Cloud Gateway to your project using Maven or Gradle.
Create a custom gateway filter factory for implementing the custom logic.
Configure the gateway routes and filters in application.yml.

2. Adding Spring Cloud Gateway Dependency

Add the following dependencies to your pom.xml:

xml

<groupId>org.springframework.cloud</groupId>

<artifactId>spring-cloud-starter-gateway</artifactId>

</dependency>

3. Custom Gateway Filters

You can create custom filters to implement debouncing, throttling, rate limiting, and exponential backoff.

3.1. Debouncing Custom Gateway Filter

Debouncing limits how often a function is invoked in quick succession by adding a delay.

Custom Debouncing Filter Factory:

java

@Component

public class DebounceGatewayFilterFactory extends AbstractGatewayFilterFactory<DebounceGatewayFilterFactory.Config> {

public DebounceGatewayFilterFactory() {

super(Config.class);

}

@Override

public GatewayFilter apply(Config config) {

return (exchange, chain) -> {

long delay = config.getDelay();

return Mono.delay(Duration.ofMillis(delay)).then(chain.filter(exchange));

};

}

public static class Config {

private long delay;

public long getDelay() {

return delay;

}

public void setDelay(long delay) {

this.delay = delay;

}

YAML Configuration for Debouncing:

yaml

spring:

cloud:

gateway:

routes:

- id: debounce_route

uri: http://example.org

filters:

- name: Debounce

args:

delay: 500

3.2. Throttling Custom Gateway Filter

Throttling limits the rate at which requests are processed over a specified period.

Custom Throttling Filter Factory:

java

@Component

public class ThrottleGatewayFilterFactory extends AbstractGatewayFilterFactory<ThrottleGatewayFilterFactory.Config> {

private final Map<String, Long> requestCounts = new ConcurrentHashMap<>();

public ThrottleGatewayFilterFactory() {

super(Config.class);

}

@Override

public GatewayFilter apply(Config config) {

return (exchange, chain) -> {

String clientIP = exchange.getRequest().getRemoteAddress().getAddress().getHostAddress();

long currentTime = System.currentTimeMillis();

requestCounts.merge(clientIP, 1L, Long::sum);

if (requestCounts.get(clientIP) > config.getMaxRequests()) {

exchange.getResponse().setStatusCode(HttpStatus.TOO_MANY_REQUESTS);

return exchange.getResponse().setComplete();

}

return chain.filter(exchange);

};

}

public static class Config {

private long maxRequests;

public long getMaxRequests() {

return maxRequests;

}

public void setMaxRequests(long maxRequests) {

this.maxRequests = maxRequests;

}

YAML Configuration for Throttling:

yaml

spring:

cloud:

gateway:

routes:

- id: throttle_route

uri: http://example.org

filters:

- name: Throttle

args:

maxRequests: 10

3.3. Rate Limiting Custom Gateway Filter

Rate limiting is used to restrict the number of requests a client can make within a specific time window.

Spring Cloud Gateway has built-in support for rate limiting via the RedisRateLimiter.

YAML Configuration for Rate Limiting:

yaml

spring:

cloud:

gateway:

routes:

- id: rate_limited_route

uri: http://example.org

filters:

- name: RequestRateLimiter

args:

redis-rate-limiter:

replenishRate: 10

burstCapacity: 20

key-resolver: "#{@remoteAddrKeyResolver}"

Key Resolver:

You need to define a key resolver to specify how the gateway will identify clients:

java

@Bean

public KeyResolver remoteAddrKeyResolver() {

return exchange -> Mono.just(exchange.getRequest().getRemoteAddress().getAddress().getHostAddress());

}

3.4. Exponential Backoff Retry Custom Gateway Filter

Exponential backoff is a retry strategy that increases the wait time between retries after each failure.

Spring Cloud Gateway has a built-in retry filter that you can configure for Exponential Backoff.

YAML Configuration for Exponential Backoff:

yaml

spring:

cloud:

gateway:

routes:

- id: exponential_backoff_route

uri: http://example.org

filters:

- name: Retry

args:

retries: 3

statuses: 500

backoff:

firstBackoff: 100ms

maxBackoff: 2s

factor: 2

jitter: true

4. Final YAML Configuration Example

Here is a complete application.yml that demonstrates how to configure different custom filters:

yaml

spring:

cloud:

gateway:

routes:

- id: debounce_route

uri: http://example.org

filters:

- name: Debounce

args:

delay: 500

- id: throttle_route

uri: http://example.org

filters:

- name: Throttle

args:

maxRequests: 10

- id: rate_limited_route

uri: http://example.org

filters:

- name: RequestRateLimiter

args:

redis-rate-limiter:

replenishRate: 10

burstCapacity: 20

key-resolver: "#{@remoteAddrKeyResolver}"

- id: exponential_backoff_route

uri: http://example.org

filters:

- name: Retry

args:

retries: 3

statuses: 500

backoff:

firstBackoff: 100ms

maxBackoff: 2s

factor: 2

jitter: true

# Redis for rate limiting

spring:

redis:

host: localhost

port: 6379

5. Key Points

Debounce Filter: Introduces a delay to prevent successive requests.
Throttle Filter: Limits the number of requests over a period of time.
Rate Limiting: Restricts the number of requests allowed using RedisRateLimiter.
Exponential Backoff: Retries failed requests with increasing delay between retries.

You can configure these custom filters based on your microservices' needs using the application.yml file. Each filter helps in managing traffic, avoiding overwhelming services, and ensuring reliable communication between services.