Implementing A/B Routing with Spring Cloud Gateway

In modern microservices architectures, routing requests based on specific criteria is a common requirement. In this post, we'll explore how to use Spring Cloud Gateway to implement A/B routing for different customers based on their customer IDs. We'll achieve this by implementing a custom filter in Spring Cloud Gateway to check the customer ID and route them to the appropriate service based on defined criteria.

Custom Filter Implementation:

import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory;
import org.springframework.stereotype.Component;
import reactor.core.publisher.Mono;

@Component
public class ABRouteFilter extends AbstractGatewayFilterFactory<ABRouteFilter.Config> {

    public ABRouteFilter() {
        super(Config.class);
    }

    @Override
    public GatewayFilter apply(Config config) {
        return (exchange, chain) -> {
            // Get the customer ID from the query parameter
            String customerId = exchange.getRequest().getQueryParams().getFirst("customerId");

            // Perform logic to determine A/B routing based on customer ID
            boolean isRouteToA = shouldRouteToA(customerId);

            // Define the target route URL
            String targetUrl = isRouteToA ? config.routeToAUrl : config.routeToBUrl;

            // Modify the request URI to route to the appropriate service
            exchange.getRequest().mutate().uri(uri -> uri.path(targetUrl).build());

            // Continue with the request chain
            return chain.filter(exchange);
        };
    }

    private boolean shouldRouteToA(String customerId) {
        // Implement logic to check customer ID and determine routing
        // This could involve database checks or other criteria
        // Return true for route to A, false for route to B
    }

    public static class Config {
        private String routeToAUrl;
        private String routeToBUrl;

        public String getRouteToAUrl() {
            return routeToAUrl;
        }

        public void setRouteToAUrl(String routeToAUrl) {
            this.routeToAUrl = routeToAUrl;
        }

        public String getRouteToBUrl() {
            return routeToBUrl;
        }

        public void setRouteToBUrl(String routeToBUrl) {
            this.routeToBUrl = routeToBUrl;
        }
    }
}

Route Definition in YAML:

spring:
  cloud:
    gateway:
      routes:
        - id: ab-routing
          uri: lb://service-discovery
          predicates:
            - Query=customerId, *
          filters:
            - name: ABRouteFilter
              args:
                routeToAUrl: /service-a
                routeToBUrl: /service-b

Perform redirection if required

When it comes to routing requests in a web application, there are scenarios where simple forwarding isn't enough. One such scenario is A/B routing, where different users are directed to different versions of a service based on certain criteria, such as customer IDs. In this section, we'll enhance our Spring Cloud Gateway setup to perform A/B routing with redirection. We'll utilize a custom filter to dynamically determine the appropriate service endpoint based on the customer ID in the request URL, and then seamlessly redirect the user's browser to the chosen service. This approach ensures a smoother user experience and better management of traffic distribution in your application. Let's dive into the implementation details.

        URI originalUri = exchange.getRequest().getURI();
        URI redirectUri = UriComponentsBuilder.fromUriString(host)
                                    .path(originalUri.getPath())
                                    .query(originalUri.getQuery())
                                    .build().toUri();
       // Perform redirection to the appropriate service URL
            return redirect(exchange, targetUrl);
        };
    }

    private Mono<Void> redirect(ServerWebExchange exchange, String targetUrl) {
        exchange.getResponse().setStatusCode(HttpStatus.SEE_OTHER);
        exchange.getResponse().getHeaders().setLocation(URI.create(targetUrl));
        return exchange.getResponse().setComplete();
    }

Conclusion

Implementing A/B routing based on customer IDs using Spring Cloud Gateway offers a flexible and scalable solution for routing requests in microservices architectures. By leveraging custom filters and route definitions, you can dynamically route requests to different services based on specific criteria, enhancing the flexibility and scalability of your system.