Spring Boot LoadBalanced
Introduction
In distributed systems, load balancing plays a crucial role in distributing incoming network traffic across multiple servers to ensure that no single server is overwhelmed. Spring Boot provides a convenient way to integrate load balancing using the @LoadBalanced annotation. In this article, we will explore the usage of Spring Boot's @LoadBalanced annotation with code examples.
What is Load Balancing?
Load balancing is the process of evenly distributing network traffic across multiple servers or nodes. It helps to optimize resource utilization, improve performance, and ensure high availability by preventing any single server from becoming a bottleneck. There are several load balancing algorithms, such as round-robin, least connections, and IP hash, that can be used to distribute the traffic.
Spring Boot LoadBalanced Annotation
Spring Boot provides a convenient way to enable load balancing using the @LoadBalanced annotation. This annotation is used to mark a RestTemplate or WebClient bean for load balancing purposes. When a RestTemplate or WebClient is marked with @LoadBalanced, it automatically gets wrapped with a load balancer interceptor that distributes the requests to multiple instances of a service.
To use the @LoadBalanced annotation, we need to add the spring-cloud-starter-loadbalancer dependency to our project. This dependency provides the load balancing capabilities for Spring Boot applications.
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-loadbalancer</artifactId>
</dependency>
LoadBalanced RestTemplate
Let's start by creating a simple Spring Boot application that demonstrates the usage of @LoadBalanced annotation with a RestTemplate. We will create a client application that calls a REST API from a server application.
First, we need to create the server application that exposes a REST API.
@RestController
public class ServerController {
@GetMapping("/hello")
public String hello() {
return "Hello, World!";
}
}
Next, we create the client application that makes a request to the server application using a RestTemplate. We annotate the RestTemplate bean with @LoadBalanced to enable load balancing.
@SpringBootApplication
public class ClientApplication {
@LoadBalanced
@Bean
public RestTemplate restTemplate() {
return new RestTemplate();
}
public static void main(String[] args) {
SpringApplication.run(ClientApplication.class, args);
}
}
In the client application, we can now use the RestTemplate to make requests to the server application. Spring Boot will automatically distribute the requests to multiple instances of the server application.
@RestController
public class ClientController {
private final RestTemplate restTemplate;
public ClientController(RestTemplate restTemplate) {
this.restTemplate = restTemplate;
}
@GetMapping("/hello")
public String hello() {
return restTemplate.getForObject("http://server-application/hello", String.class);
}
}
LoadBalanced WebClient
Besides RestTemplate, Spring Boot also supports load balancing with WebClient. WebClient is a non-blocking, reactive HTTP client introduced in Spring WebFlux.
To use WebClient with load balancing, we need to create a WebClient.Builder bean and wrap it with a load balancer interceptor using the build() method. We can then use this WebClient bean to make requests to the server application.
@SpringBootApplication
public class ClientApplication {
@LoadBalanced
@Bean
public WebClient.Builder webClientBuilder() {
return WebClient.builder();
}
public static void main(String[] args) {
SpringApplication.run(ClientApplication.class, args);
}
}
Now, we can use the WebClient to make requests to the server application. The load balancer interceptor will distribute the requests to multiple instances of the server application.
@RestController
public class ClientController {
private final WebClient.Builder webClientBuilder;
public ClientController(WebClient.Builder webClientBuilder) {
this.webClientBuilder = webClientBuilder;
}
@GetMapping("/hello")
public Mono<String> hello() {
return webClientBuilder.build()
.get()
.uri("http://server-application/hello")
.retrieve()
.bodyToMono(String.class);
}
}
Conclusion
In this article, we explored the usage of Spring Boot's @LoadBalanced annotation to enable load balancing in a distributed system. We learned how to use the @LoadBalanced annotation with RestTemplate and WebClient. By using load balancing, we can distribute incoming network traffic across multiple servers, optimize resource utilization, and improve the performance and availability of our applications.
To summarize, the @LoadBalanced annotation in Spring Boot provides a convenient way to integrate load balancing into our applications, making them more scalable and reliable.
<details> <summary>Mermaid syntax for pie chart</summary>
pie
title Load Balancing Algorithms
"Round Robin" : 45
"Least Connections" : 30
"IP Hash" : 25
</details>
journey
title Spring Boot LoadBalanced
section Server
