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Spring WebFlux WebClient resilience and performance

I just test by sample PoC project some blocking / non blocking solutions in simple common scenario.


  • There are rest blocking endpoint which is quite slow - each request tooks 200 ms.
  • There are other - client application, which call this slow endpoint.

I have tested current (blocking) Spring boot client (tomcat), Spring Boot 2.0 (netty) with WebFlux - WebClient, Ratpack and Lagom. In each cases I have stressed client application by gatling test simple scenario (100-1000 users / second).

I have tested ratpack and lagom as reference non blocking io servers to compare results to spring boot (blocking and non blocking).

In all cases i have results as expected, except spring boot 2.0 test. Its working only for small load levels but even then with high latency. If load level rises up - all requests are time outed.

WebClient usage :

public class NonBlockingClientController {
private WebClient client = WebClient.create("http://localhost:9000");

public Mono<String> getData() {
    return client.get()
            .then(response -> response.bodyToMono(String.class));

I have no idea what goes wrong or current snapshot version just working that.

All sources published at

  • blocking-service - slow blocking endpoint
  • non-blocking-client - Spring Boot 2.0 and WebClient based client

I just created a simple Spring Boot application using spring-boot-starter-webflux with version 2.0.0.BUILD-SNAPSHOT which brings spring-webflux version 5.0.0.BUILD-SNAPSHOT and same for Spring Core, Beans, Context, etc.


  1. Issue no longer exists after 5.0 RC4 release. The issue was related to connection pooling in reactor-netty and reactor-core.

    I've also tested with Spring Boot 2.0.0.M4 - everything looks fine now.