Spring Cloud Circuit Breaker3.1.2

Introduction

Spring Cloud Circuit breaker provides an abstraction across different circuit breaker implementations. It provides a consistent API to use in your applications allowing you the developer to choose the circuit breaker implementation that best fits your needs for your app.

Supported Implementations

• Resilience4J

• Spring Retry

Core Concepts

To create a circuit breaker in your code you can use the CircuitBreakerFactory API. When you include a Spring Cloud Circuit Breaker starter on your classpath a bean implementing this API will automatically be created for you. A very simple example of using this API is given below

@Service
public static class DemoControllerService {
	private RestTemplate rest;
	private CircuitBreakerFactory cbFactory;

	public DemoControllerService(RestTemplate rest, CircuitBreakerFactory cbFactory) {
		this.rest = rest;
		this.cbFactory = cbFactory;
	}

	public String slow() {
		return cbFactory.create("slow").run(() -> rest.getForObject("/slow", String.class), throwable -> "fallback");
	}

}

The CircuitBreakerFactory.create API will create an instance of a class called CircuitBreaker. The run method takes a Supplier and a Function. The Supplier is the code that you are going to wrap in a circuit breaker. The Function is the fallback that will be executed if the circuit breaker is tripped. The function will be passed the Throwable that caused the fallback to be triggered. You can optionally exclude the fallback if you do not want to provide one.

Circuit Breakers In Reactive Code

If Project Reactor is on the class path then you can also use ReactiveCircuitBreakerFactory for your reactive code.

@Service
public static class DemoControllerService {
	private ReactiveCircuitBreakerFactory cbFactory;
	private WebClient webClient;


	public DemoControllerService(WebClient webClient, ReactiveCircuitBreakerFactory cbFactory) {
		this.webClient = webClient;
		this.cbFactory = cbFactory;
	}

	public Mono<String> slow() {
		return webClient.get().uri("/slow").retrieve().bodyToMono(String.class).transform(
		it -> cbFactory.create("slow").run(it, throwable -> return Mono.just("fallback")));
	}
}

The ReactiveCircuitBreakerFactory.create API will create an instance of a class called ReactiveCircuitBreaker. The run method takes with a Mono or Flux and wraps it in a circuit breaker. You can optionally profile a fallback Function which will be called if the circuit breaker is tripped and will be passed the Throwable that caused the failure.