API gateway Spring Boot

Spring Boot is an open-source Java-based framework used to create stand-alone, production-grade web applications and services. It is built on top of the Spring framework and provides a convenient way to set up a Spring-based application with minimal configuration.

An API gateway is a component that sits between your backend services and your API clients. It acts as a reverse proxy, routing requests from clients to the appropriate backend service and then returning the service’s response back to the client. An API gateway can also perform tasks such as authentication, rate limiting, and caching.

Spring Cloud Gateway is a lightweight, reactive API gateway built on top of the Spring framework. It is designed to provide a simple, yet powerful way to route and manage network traffic to your applications. 

Spring Cloud Gateway uses a reactive, non-blocking architecture that can scale to handle a large number of concurrent requests. It can be used to route traffic to different backend services based on the incoming request, perform authentication and authorization, and perform other tasks such as rate limiting and caching.

Spring Boot and Spring Cloud Gateway are both frameworks that are built on top of the Spring framework and are used for building Java-based applications. However, they serve different purposes and are typically used in different parts of an application.

Spring Boot is a framework for building standalone, production-grade Spring-based applications. It provides a pre-configured set of libraries and components that can be easily integrated into new applications, and it can automatically configure and set up the application for you. This makes it a great tool for quickly developing and deploying new Spring-based applications.

Spring Cloud Gateway is a framework for building microservices-based applications. It provides support for routing and filtering incoming requests to microservices, as well as support for other common features needed to build a microservices architecture. It is typically used as an API Gateway in a microservices-based application.

Spring Cloud Gateway is important because it provides a simple, yet powerful way to route and manage network traffic to your applications. It is particularly well-suited for cloud native applications, as it is built on top of the Spring framework and uses a reactive, non-blocking architecture that can scale to handle a large number of concurrent requests.

Spring Cloud Gateway works by sitting between your API clients and your backend services. It acts as a reverse proxy, routing requests from clients to the appropriate backend service and then returning the service’s response back to the client. Spring Cloud Gateway uses a routing table to determine how to route incoming requests to the appropriate backend service. This routing table can be configured based on the incoming request’s path, host, and other request metadata.

Spring Cloud Gateway also provides a number of built-in filters that can be used to perform tasks such as authentication, rate limiting, and caching. These filters can be configured and combined to create custom request processing logic.

Prerequisites

To get started with Spring Cloud API Gateway, you will need to have the following prerequisites:

• Java 8 or later
• Maven 3.2 or later
• An IDE such as Eclipse or IntelliJ IDEA

Step 1: Create Maven project

Create a new Maven project in your IDE, and add the following dependencies to your pom.xml file:

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

    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
<version>4.0.0</version>
  </dependency>
</dependencies>

These dependencies will enable your application to use the Eureka service registry and the Zuul API gateway.

Step 2: Create a new configuration class

Create a new configuration class and annotate it with @EnableZuulProxy to enable the API gateway:

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

Step 3: Create applications.properties file

Create a new application.properties file in the src/main/resources directory and add the following configuration to enable Eureka client functionality:

eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/

This will configure your API gateway to use the Eureka service registry running on the local host at port 8761.

Note: If you are running it on a production server, you will probably need to open this port on your firewall.

Step 4: Add routes configuration in application.properties

In the application.properties file, add the following configuration to enable the API gateway to route requests to the appropriate backend service:

zuul.routes.your-service-name.path=/your-service-path/**
zuul.routes.your-service-name.serviceId=your-service-name

This will configure the API gateway to route requests with a path starting with /your-service-path/ to the service with the ID your-service-name registered in the Eureka service registry.

Step 5: Start Eureka server

Start the Eureka server and register your backend services with it. Then, start the API gateway application and it will automatically register itself with the Eureka server and begin routing requests to the appropriate backend services.

Step 6: Customization

To customize the routing behavior of your Spring Cloud API Gateway, you can use the RouteLocator interface and ZuulRoute class.

Create a new configuration class and define a bean of type RouteLocator:

@Configuration
public class GatewayConfiguration {

  @Bean
  public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
    // define your routing rules here
    return builder.routes()
        .build();
  }
}

To define a routing rule, you can use the route method of the RouteLocatorBuilder and specify the path, service ID, and any other relevant information:

@Bean
public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
  return builder.routes()
      .route("route-name", r -> r.path("/route-path/**")
          .filters(f -> f.addRequestHeader("X-Location", "USA"))
          .uri("http://localhost:8080"))
      .build();
}

This routing rule will route requests with a path starting with /route-path/ to the URI http://localhost:8080, and will add a request header with the key X-Location and value USA to the forwarded request.

To use dynamic routing, you can use the DiscoveryClientRouteLocator provided by Spring Cloud. This class allows you to route requests to services registered in a service registry, such as Eureka or Consul:

@Bean
public RouteLocator customRouteLocator(DiscoveryClient dc, DiscoveryLocatorProperties dlp) {
  return new DiscoveryClientRouteLocator(dc, dlp);
}

This will route requests to the appropriate service based on the service ID specified in the request path. For example, a request to /service-id/resource-path will be routed to the service with the ID service-id.

Several factors are reshaping how users evaluate API gateways:

• How well does it scale to handle a larger volume of API traffic?
• How well does it perform at a larger scale? 
• How well does it consistently deliver low-latency response times? 
• Does it natively work in public cloud or any Kubernetes environments?
• Does it leverage the latest innovations in proxy technologies (e.g. Envoy Proxy)? 
• Does it leverage the latest open source innovations around proxy technologies (e.g. WebAssembly or GraphQL)?

As each of these issues become more impactful to how an API gateway can enable your microservice applications, the more companies are beginning to choose Solo.io Gloo Gateway. Based on Envoy Proxy, Gloo Gateway enables greater scalability and latency than legacy API gateways based on NGINX, HAProxy, or Java-wrappers on proxy technology. 

In addition, Gloo Gateway is both public cloud native and Kubernetes native, so integrating with DevOps environments is seamless. And Gloo Gateway enables users to easily add new innovations such as Web Assembly or GraphQL to their API Gateway environment to handle next-generation application needs. 

Learn more about Solo Gloo Gateway.