Add metrics when the connections limit is set

When the HTTP connection limit is set:

- expose a new gauge with the max number of connections
- expose a new gauge with the current number of connections
- expose a new counter with the number of rejected connections

extensions/micrometer/deployment/src/test/java/io/quarkus/micrometer/deployment/binder/VertxConnectionMetricsTest.java

@@ -0,0 +1,108 @@
+package io.quarkus.micrometer.deployment.binder;
+
+import static org.awaitility.Awaitility.await;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import jakarta.enterprise.context.ApplicationScoped;
+import jakarta.enterprise.event.Observes;
+import jakarta.inject.Inject;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.Gauge;
+import io.micrometer.core.instrument.Metrics;
+import io.quarkus.runtime.StartupEvent;
+import io.quarkus.test.QuarkusUnitTest;
+import io.restassured.RestAssured;
+import io.vertx.mutiny.ext.web.Router;
+
+/**
+ * Verify that we report connection metrics when the connection limit it set.
+ */
+public class VertxConnectionMetricsTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .withConfigurationResource("test-logging.properties")
+            .overrideConfigKey("quarkus.redis.devservices.enabled", "false")
+            // Only allows 2 concurrent connections
+            .overrideConfigKey("quarkus.http.limits.max-connections", "2")
+            // Close the connection after 1s of inactivity, otherwise, the connection are kept open for 30min
+            .overrideConfigKey("quarkus.http.idle-timeout", "1s")
+            .withApplicationRoot(jar -> jar.addClasses(App.class));
+
+    @Inject
+    App app;
+
+    private ExecutorService executor;
+    private int concurrency;
+
+    @BeforeEach
+    public void init() {
+        concurrency = 10;
+        executor = Executors.newFixedThreadPool(10); // More than the connection limit
+    }
+
+    @AfterEach
+    public void cleanup() {
+        executor.shutdown();
+    }
+
+    @Test
+    void testConnectionMetrics() throws InterruptedException {
+        AtomicInteger rejected = new AtomicInteger();
+        CountDownLatch latch = new CountDownLatch(concurrency);
+        for (int i = 0; i < concurrency; i++) {
+            executor.submit(() -> {
+                try {
+                    RestAssured.get("/ok").statusCode();
+                } catch (Exception e) {
+                    // RestAssured considers the rejection as an error.
+                    rejected.incrementAndGet();
+                } finally {
+                    latch.countDown();
+                }
+            });
+        }
+
+        Assertions.assertThat(latch.await(10, TimeUnit.SECONDS)).isTrue();
+        Gauge max = Metrics.globalRegistry.find("vertx.http.connections.max").gauge();
+        Gauge current = Metrics.globalRegistry.find("vertx.http.connections.current").gauge();
+        Assertions.assertThat(max).isNotNull();
+        Assertions.assertThat(current).isNotNull();
+
+        Assertions.assertThat(max.value()).isEqualTo(2);
+
+        // All requests are done, and connection closed (idle timeout)
+        await().untilAsserted(() -> Assertions.assertThat(current.value()).isEqualTo(0));
+
+        if (rejected.get() > 0) {
+            Counter counter = Metrics.globalRegistry.find("vertx.http.connections.rejected").counter();
+            Assertions.assertThat(counter).isNotNull();
+            Assertions.assertThat(counter.count()).isGreaterThan(0);
+        }
+    }
+
+    @ApplicationScoped
+    public static class App {
+
+        public void start(@Observes StartupEvent ev, Router router, io.vertx.core.Vertx vertx) {
+            router.get("/ok").handler(rc -> {
+                // Keep the connection open for 100ms.
+                vertx.setTimer(250, l -> rc.endAndForget("ok"));
+            });
+        }
+
+    }
+
+}

extensions/micrometer/runtime/src/main/java/io/quarkus/micrometer/runtime/binder/vertx/VertxMeterBinderAdapter.java

@@ -1,11 +1,17 @@
 package io.quarkus.micrometer.runtime.binder.vertx;
 
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
+
 import org.jboss.logging.Logger;
 
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.Gauge;
 import io.micrometer.core.instrument.Metrics;
 import io.micrometer.core.instrument.Tag;
 import io.micrometer.core.instrument.Tags;
 import io.quarkus.micrometer.runtime.binder.HttpBinderConfiguration;
+import io.quarkus.vertx.http.runtime.ExtendedQuarkusVertxHttpMetrics;
 import io.vertx.core.VertxOptions;
 import io.vertx.core.datagram.DatagramSocketOptions;
 import io.vertx.core.http.HttpClientOptions;
@@ -25,7 +31,8 @@
 import io.vertx.core.spi.metrics.TCPMetrics;
 import io.vertx.core.spi.metrics.VertxMetrics;
 
-public class VertxMeterBinderAdapter extends MetricsOptions implements VertxMetricsFactory, VertxMetrics {
+public class VertxMeterBinderAdapter extends MetricsOptions
+        implements VertxMetricsFactory, VertxMetrics, ExtendedQuarkusVertxHttpMetrics {
     private static final Logger log = Logger.getLogger(VertxMeterBinderAdapter.class);
     public static final String METRIC_NAME_SEPARATOR = "|";
 
@@ -184,4 +191,39 @@ private String extractClientName(String mn) {
         return null;
     }
 
+    @Override
+    public ConnectionTracker getHttpConnectionTracker() {
+        return new ConnectionTracker() {
+
+            private final Counter counter = Counter.builder("vertx.http.connections.rejected")
+                    .description("Number of rejected HTTP connections")
+                    .register(Metrics.globalRegistry);
+
+            @Override
+            public void onConnectionRejected() {
+                counter.increment();
+            }
+
+            @Override
+            public void initialize(int maxConnections, AtomicInteger current) {
+                Gauge.builder("vertx.http.connections.current", new Supplier<Number>() {
+                    @Override
+                    public Number get() {
+                        return current.get();
+                    }
+                })
+                        .description("Current number of active HTTP connections")
+                        .register(Metrics.globalRegistry);
+
+                Gauge.builder("vertx.http.connections.max", new Supplier<Number>() {
+                    @Override
+                    public Number get() {
+                        return maxConnections;
+                    }
+                })
+                        .description("Max number of HTTP connections")
+                        .register(Metrics.globalRegistry);
+            }
+        };
+    }
 }

extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/ExtendedQuarkusVertxHttpMetrics.java

@@ -0,0 +1,41 @@
+package io.quarkus.vertx.http.runtime;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * An interface extending the metrics exposed for the Vert.x HTTP server.
+ * <p>
+ * The Vert.x HTTP metrics are managed by Vert.x, and are exposed by the Vert.x metrics SPI.
+ * However, some of the metrics are not exposed by the SPI, and are only available through the Vert.x HTTP SPI.
+ * <p>
+ * Thus, we need to extend the Vert.x HTTP metrics SPI to expose these metrics.
+ */
+public interface ExtendedQuarkusVertxHttpMetrics {
+
+    /**
+     * A no-op connection tracker.
+     */
+    ConnectionTracker NOOP_CONNECTION_TRACKER = new ConnectionTracker() {
+        @Override
+        public void onConnectionRejected() {
+        }
+
+        @Override
+        public void initialize(int maxConnections, AtomicInteger current) {
+        }
+    };
+
+    /**
+     * Gets a tracker to report the number of active HTTP connection, the number of rejected connections, etc.
+     *
+     * @return the tracker.
+     */
+    ConnectionTracker getHttpConnectionTracker();
+
+    interface ConnectionTracker {
+
+        void onConnectionRejected();
+
+        void initialize(int maxConnections, AtomicInteger current);
+    }
+}

extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/VertxHttpRecorder.java

@@ -1123,8 +1123,14 @@ private void setupUnixDomainSocketHttpServer(HttpServer httpServer, HttpServerOp
 
         private void setupTcpHttpServer(HttpServer httpServer, HttpServerOptions options, boolean https,
                 Promise<Void> startFuture, AtomicInteger remainingCount, AtomicInteger currentConnectionCount) {
+
             if (quarkusConfig.limits.maxConnections.isPresent() && quarkusConfig.limits.maxConnections.getAsInt() > 0) {
+                var tracker = vertx.isMetricsEnabled()
+                        ? ((ExtendedQuarkusVertxHttpMetrics) ((VertxInternal) vertx).metricsSPI()).getHttpConnectionTracker()
+                        : ExtendedQuarkusVertxHttpMetrics.NOOP_CONNECTION_TRACKER;
+
                 final int maxConnections = quarkusConfig.limits.maxConnections.getAsInt();
+                tracker.initialize(maxConnections, currentConnectionCount);
                 httpServer.connectionHandler(new Handler<HttpConnection>() {
 
                     @Override
@@ -1135,6 +1141,7 @@ public void handle(HttpConnection event) {
                             if (current == maxConnections) {
                                 //just close the connection
                                 LOGGER.debug("Rejecting connection as there are too many active connections");
+                                tracker.onConnectionRejected();
                                 event.close();
                                 return;
                             }
@@ -1143,7 +1150,7 @@ public void handle(HttpConnection event) {
                             @Override
                             public void handle(Void event) {
                                 LOGGER.debug("Connection closed");
-                                connectionCount.decrementAndGet();
+                                currentConnectionCount.decrementAndGet();
                             }
                         });
                     }