How to Build an API Gateway With Netflix's Zuul and Spring Boot

When you develop applications in a microservices architecture, it is often required to route API requests to the respective service(s). Doing this with a general-purpose load balancer like Nginx or Apache was the practice before, but it takes some control away from the application. Also, it is important to remember that maintaining an API-Gateway service brings you more benefits other than load balancing like below.

• Authentication and Security
• Monitoring
• Dynamic Routing
• Static Response handling
• Rate limiting

You can implement all the above features with Spring Boot + Zuul, but this article will only cover how to create your first API-Gateway application. Let's start with an example.

Here, we have multiple services executing their own business logic, so it is up to the "Gateway" to send requests to the correct microservice. This "Gateway" is a layer 7 load balancer, which routes requests to the correct microservice based on the information presented in the request URL.

Layer 4 load balancer bases the load-balancing decision on the source and destination IP addresses and ports recorded in the packet header, without considering the contents of the packet while layer 7 load balancers base their routing decisions on various characteristics of the HTTP header and on the actual contents of the message, such as the URL, the type of data (text, video, graphics), or information in a cookie. Nginx

Netflix Zuul to the Rescue

Zuul is a library developed by Netflix that provides dynamic routing, monitoring, resiliency, security, and more amazing features. The best thing is Spring Boot has already bundled Zuul with their Spring Cloud dependency. Let's see how we can implement our own API Gateway with Spring Cloud + Zuul.

1. Generate the Spring Boot project. Go to Spring Initializer page and add Zuul as a dependency.
2. Download and extract the project.
3. You just need to add @EnableZuulProxy annotation to the Main class to make this project a Zuul proxy server. Spring Boot will auto-configure everything based on this annotation.

package xyz.devreads.apigateway;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.zuul.EnableZuulProxy;

@SpringBootApplication
@EnableZuulProxy
public class ApiGatewayApplication {
   public static void main(String[] args) {
      SpringApplication.run(ApiGatewayApplication.class, args);
   }
}

4. Now you can configure routing (i.e. Request paths and respective service URLs) in the application.properties file.
   

server.port = 8080
spring.application.name = api-gateway
# routing for service 1
zuul.routes.service_1.path = /api/service_1/**
zuul.routes.service_1.url = http://localhost:8081/
# routing for service 2
zuul.routes.service_2.path = /api/service_2/**
zuul.routes.service_2.url = http://localhost:8082/

5. Execute mvn clean install to build the project. Then run it using java –jar . You will see the API-Gateway is starting to listen on port 8080.
6. Send two requests to http://localhost:8080/api/service_1/ and http://localhost:8080/api/service_2/, you will see requests are routed to service_1 and service_2 respectively, as we have configured on application.properties file.

Did you see how awesome Spring Boot + Zuul is? We were able to configure an API-Gateway application with just one annotation and a couple of configuration entries.

Thanks for reading, and let me know your thoughts in the comments!