@Override
    public void preRequestChecks(HttpRequestMessage zuulRequest) {
        if (concurrencyProtectionEnabled.get() && concurrentRequests.get() > concurrencyMax.get()) {
            rejectedRequests.increment();
            throw new OriginConcurrencyExceededException(getName());
        }

        concurrentRequests.incrementAndGet();
    }
Netty Origin basic implementation that can be used for most apps, with the more complex methods having no-op
implementations.

Author: Arthur Gonigberg
Date: December 01, 2017
zuul-core/src/main/java/com/netflix/zuul/origins/BasicNettyOrigin.java