reactor-core/src/main/java/reactor/core/publisher/Flux.java
public final Flux<T> metrics() {
		if (!Metrics.isInstrumentationAvailable()) {
			return this;
		}

		if (this instanceof Fuseable) {
			return onAssembly(new FluxMetricsFuseable<>(this));
		}
		return onAssembly(new FluxMetrics<>(this));
	}
public final Flux<T> metrics() {
		if (!Metrics.isInstrumentationAvailable()) {
			return this;
		}

		if (this instanceof Fuseable) {
			return onAssembly(new FluxMetricsFuseable<>(this));
		}
		return onAssembly(new FluxMetrics<>(this));
	}
Activate metrics for this sequence, provided there is an instrumentation facade
on the classpath (otherwise this method is a pure no-op).
<p>
Metrics are gathered on {@link Subscriber} events, and it is recommended to also
{@link #name(String) name} (and optionally {@link #tag(String, String) tag}) the
sequence.

@return an instrumented {@link Flux}