Metrics 5.0 (MicroProfile 6.0) implementation uncorrect behaviours

[andreaminutoibm]

Gauge metrics from Metrics 5.0 implementation don't work as expected, at least for my understanding of the specification.

Versions:

• OpenLiberty version: 23.0.0.3
• MicroProfile version: 6.0
• Metrics version: 5.0

Features:

• servlet-6.0
• mpMetrics-5.0

Problems:

1. Using @Gauge annotation, a gauge metric is not registered at runtime and doesn't show up when called by /metrics API
2. Using manually registered method, the gauge metric shows up when called by /metrics API but it is shown as a float number even though it has been registered as an Integer.

Scenario: Suppose we are implementing a servlet that must contain a gauge metric to report the number of active requests.

Problem 1: Sample code (the metric is not registered at runtime)

@WebServlet(name = "MyServlet",  urlPatterns = {"/myservlet"})
public class MyServlet extends HttpServlet
{
   @Serial
   private static final long serialVersionUID = 93456419673850054L;

   // Counter
   private final AtomicInteger activeRequests = new AtomicInteger(0);

   @Gauge(name = "myservlet_active_requests", description = "MyServlet active requests", absolute = true, unit = MetricUnits.NONE)
   public Integer getActiveRequests()
   {
      return activeRequests.get();
   }
}

Problem 2: Sample code (the metric is registered but it shows up as a float number)

@WebServlet(name = "MyServlet",  urlPatterns = {"/myservlet"})
public class MyServlet extends HttpServlet
{
   @Serial
   private static final long serialVersionUID = 93456419673850054L;

   // Counter
   private final AtomicInteger activeRequests = new AtomicInteger(0);

   public Integer getActiveRequests()
   {
      return activeRequests.get();
   }

   @Inject
   @RegistryScope(scope= MetricRegistry.APPLICATION_SCOPE)
   MetricRegistry metricRegistry;

   public void init(ServletConfig config) throws ServletException
   {
      Metadata m = Metadata.builder()
                              .withName("myservlet_active_requests")
                              .withDescription("MyServlet active requests")
                              .withUnit(MetricUnits.NONE)
                              .build();

      metricRegistry.gauge(m, this::getActiveRequests);
   }
}

The /metrics?scope=application api reports:

# HELP myservlet_active_requests MyServlet active requests
# TYPE myservlet_active_requests gauge
myservlet_active_requests{mp_scope="application",} 12.0

[Channyboy]

Hello @andreaminutoibm, 1. CDI does not consider all targets on a servlet to be "intercept-able". We recommend to use a RestfulWS (formerly JAX-RS) if you intend to instrument with annotations.

2. In mpMetrics-5.0 the underlying implementation is now using micrometer metrics. As a consequence of this, the exporting of metrics to /metrics uses the Prometheus client library which formats the metrics into float values.

[Channyboy]

@andreaminutoibm Is this okay to close?

[andreaminutoibm]

It’s ok to close for me. Thank you.

Andrea Minuto

Andrea Minuto Executive IT Specialist IBM Expert Labs Red Hat Certified Architect

39 335 143 3009 Mobile @.**@.> Via Luigi Stipa, 150 00148 ROMA (Italia)

From: David Chan @.> Sent: mercoledì 24 maggio 2023 20:17 To: OpenLiberty/open-liberty @.> Cc: Andrea Minuto @.>; Mention @.> Subject: [EXTERNAL] Re: [OpenLiberty/open-liberty] Metrics 5.0 (MicroProfile 6.0) implementation uncorrect behaviours (Issue #25032)

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