How to use Resilience4j Circuit Breaker with WebFlux in Spring Boot - spring-boot

Question

I have service A that calls downstream service B.
Service A code
#RestController
#RequestMapping(value = "", produces = MediaType.APPLICATION_JSON_VALUE)
public class GreetingController {
private final GreetingService greetingService;
public GreetingController(GreetingService greetingService){
this.greetingService = greetingService;
}
#GetMapping(value = "/greetings")
public Mono<String> getGreetings() {
return greetingService.callServiceB();
}
}
#Component
#RequiredArgsConstructor
public class GreetingService {
CircuitBreaker circuitBreaker = CircuitBreaker.ofDefaults("greetingService");
Callable<Mono<String>> callable = CircuitBreaker.decorateCallable(circuitBreaker, this::clientCall);
Future<Mono<String>> future = Executors.newSingleThreadExecutor().submit(callable);
public Mono<String> callServiceB() {
try {
return future.get();
} catch (CircuitBreakerOpenException | InterruptedException | ExecutionException ex){
return Mono.just("Service is down!");
}
}
private final String url = "/v1/holidaysgreetings";
private Mono<String> clientCall(){
WebClient client = WebClient.builder().baseUrl("http://localhost:8080").build();
return client
.get()
.uri(url)
.retrieve()
.bodyToMono(String.class);
}
when i shut down downstream service B(running on localhost:8080) and hit /greetings endpoint in GreetingsController class to see if my circuit breaker is working properly or not, i get very this nasty error
2021-06-28 21:27:31.431 ERROR 10285 --- [nio-8081-exec-7] o.a.c.c.C.[.[.[.[dispatcherServlet]: Servlet.service() for servlet [dispatcherServlet] in context with path [/v1/holidaysgreetings]
threw exception [Request processing failed; nested exception is org.springframework.web.reactive.function.client.WebClientRequestException: Connection refused: localhost/127.0.0.1:8080;
nested exception is io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: localhost/127.0.0.1:8080] with root cause
java.net.ConnectException: Connection refused
Anyone knows why i am getting this? What i am missing here? Am i implementing circuit breaker correctly?

Answer 1

You are mixing reactive libraries with regular non-reactive libraries. If you aim to use spring-webflux it is better to use the reactor-resilience4j together with the regular reactor-adapter library.
Use these imports:
implementation 'org.springframework.boot:spring-boot-starter-webflux'
implementation 'org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j'
implementation "io.projectreactor.addons:reactor-adapter:${reactorVersion}"
You are also not creating the circuit-breaker service that you can rely on. After creating it you can call the " Mono run(Mono toRun, Function<Throwable, Mono> fallback)" (to the one that return a Flux if you want) to execute your service and provide a fallback.
Here is one example from a demo code.
#RestController
public class CompletableFutureDemoController {
Logger LOG = LoggerFactory.getLogger(CompletableFutureDemoController.class);
private CompletableFutureHttpBinService httpBin;
private ReactiveCircuitBreakerFactory reactiveCircuitBreakerFactory;
public CompletableFutureDemoController(CompletableFutureHttpBinService httpBin, ReactiveCircuitBreakerFactory reactiveCircuitBreakerFactory) {
this.httpBin = httpBin;
this.reactiveCircuitBreakerFactory = reactiveCircuitBreakerFactory;
}
#GetMapping("/completablefuture/delay/{seconds}")
public Mono<Map> delay(#PathVariable int seconds) {
return reactiveCircuitBreakerFactory.create("completablefuturedelay")
.run(Mono.fromFuture(httpBin.delay(seconds)), t -> {
LOG.warn("delay call failed error", t);
Map<String, String> fallback = new HashMap();
fallback.put("hello", "world");
return Mono.just(fallback);
}
);
}
}