How to set event-loop pool size in Spring Webflux / WebClient?

Question

In multi-reactor framework such as Vert.X we can set the number of event-loop threads, e.g.:

final VertxOptions vertxOptions = new VertxOptions();
vertxOptions.setEventLoopPoolSize(16);
final Vertx myVertx = Vertx.vertx(vertxOptions);

How to do the equivalent in Spring Boot 2 WebFlux / WebClient?

Answer 1

You have two options:

1. Override ReactiveWebServerFactory bean with a customizer that applies event loop resources config:

   @Bean
   public ReactiveWebServerFactory reactiveWebServerFactory() {
       NettyReactiveWebServerFactory factory = new NettyReactiveWebServerFactory();
       factory.addServerCustomizers(builder -> builder.loopResources(LoopResources.create("my-http", 16, true)));
   
       return factory;
   }
   

2. Or use -Dreactor.ipc.netty.workerCount=16 environment variable. By default it's value is set to Math.max(availableProcessors(), 4). Example: java -jar your-app.jar -Dreactor.ipc.netty.workerCount=16