Provide a metric that measures the time for authorizing

[minwoox]

Usually, it takes a long to authorize a request because the authorizer mostly needs to call another backend.
It would be nice if we provide a timer for the AuthService so that users easily get to know how long it takes.

[erie0210]

Can you specify how users get to know the timer? (How to provide time for the user.) Should it be like return with response field? or would it be better in header? :)

[minwoox]

Hi!
We can create a timer using Micrometer API and register it to MeterRegistry.
(You might want to refer to these lines of code)

armeria/core/src/main/java/com/linecorp/armeria/common/metric/MoreMeters.java

Lines 137 to 159 in 5ff371e

	public static Timer newTimer(MeterRegistry registry, String name, Iterable<Tag> tags) {
	requireNonNull(registry, "registry");
	requireNonNull(name, "name");
	requireNonNull(tags, "tags");
	final Double maxExpectedValueNanos = distStatCfg.getMaximumExpectedValueAsDouble();
	final Double minExpectedValueNanos = distStatCfg.getMinimumExpectedValueAsDouble();
	final Duration maxExpectedValue =
	maxExpectedValueNanos != null ? Duration.ofNanos(maxExpectedValueNanos.longValue()) : null;
	final Duration minExpectedValue =
	minExpectedValueNanos != null ? Duration.ofNanos(minExpectedValueNanos.longValue()) : null;
	return Timer.builder(name)
	.tags(tags)
	.maximumExpectedValue(maxExpectedValue)
	.minimumExpectedValue(minExpectedValue)
	.publishPercentiles(distStatCfg.getPercentiles())
	.publishPercentileHistogram(distStatCfg.isPercentileHistogram())
	.percentilePrecision(distStatCfg.getPercentilePrecision())
	.distributionStatisticBufferLength(distStatCfg.getBufferLength())
	.distributionStatisticExpiry(distStatCfg.getExpiry())
	.register(registry);
	}

If so, we can get the information using by looking at the registry. We don't have to return to the client or whoever.
Usually, the collected registy is sent to the collector such as Prometheus, so that we can investigate if something happens later.

If you are not familiar with metric, I recommend you to read this document:
https://micrometer.io/docs/concepts

After that, we can create a timer in the AuthService and measure the duration here:

armeria/core/src/main/java/com/linecorp/armeria/server/auth/AuthService.java

Lines 88 to 91 in 4cc5b8b

	public HttpResponse serve(ServiceRequestContext ctx, HttpRequest req) throws Exception {
	return HttpResponse.from(AuthorizerUtil.authorizeAndSupplyHandlers(authorizer, ctx, req)
	.handleAsync((result, cause) -> {
	try {

Then, we can call this API to record it:
timer.record(duration, TimeUnit.NANOSECONDS)

Please, let me know if you have any further questions. 😉