OAP-211 Metric to count the number of active metrics for prometheus

oap-stdlib-test/src/test/java/oap/prometheus/PrometheusExporterTest.java

@@ -24,20 +24,20 @@
 
 package oap.prometheus;
 
-import io.micrometer.core.instrument.Counter;
 import io.micrometer.core.instrument.Metrics;
 import oap.http.Client;
 import oap.http.server.nio.NioHttpServer;
 import oap.testng.EnvFixture;
 import oap.testng.Fixtures;
+import org.testng.annotations.AfterMethod;
 import org.testng.annotations.Test;
 
 import java.io.IOException;
+import java.util.concurrent.TimeUnit;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 public class PrometheusExporterTest extends Fixtures {
-    private static final Counter TEST_1 = Metrics.counter( "test1" );
     private final EnvFixture envFixture;
 
     public PrometheusExporterTest() {
@@ -49,16 +49,34 @@ public void server() throws IOException {
         var port = envFixture.portFor( "prometheus" );
         try( var server = new NioHttpServer( new NioHttpServer.DefaultPort( port ) ) ) {
             var exporter = new PrometheusExporter( server );
+
+            var metric1 = Metrics.counter( "test1" );
+            var metric2 = Metrics.timer( "test2" );
+
             server.start();
 
-            TEST_1.increment( 2 );
+            metric1.increment( 2 );
+            metric2.record( 2, TimeUnit.SECONDS );
+
             var response = Client.DEFAULT.get( "http://localhost:" + port + "/metrics" ).contentString();
             assertThat( response ).contains( """
                 # HELP test1_total \s
                 # TYPE test1_total counter
                 test1_total 2.0
                 """ );
+            assertThat( response ).contains( "test2_seconds_count 1.0" );
+            assertThat( response ).contains( "test2_seconds_max 2.0" );
+            assertThat( response ).contains( "system_metrics_total 5.0" );
         }
     }
 
+    @AfterMethod
+    public void beforeMethod() {
+        PrometheusExporter.prometheusRegistry.getPrometheusRegistry().clear();
+    }
+
+    @AfterMethod
+    public void afterMethod() {
+        PrometheusExporter.prometheusRegistry.getPrometheusRegistry().clear();
+    }
 }

oap-stdlib/src/main/java/oap/prometheus/PrometheusExporter.java

@@ -27,18 +27,21 @@
 import io.micrometer.core.instrument.Metrics;
 import io.micrometer.prometheus.PrometheusConfig;
 import io.micrometer.prometheus.PrometheusMeterRegistry;
+import io.prometheus.client.exporter.common.TextFormat;
 import lombok.extern.slf4j.Slf4j;
 import oap.http.server.nio.HttpHandler;
 import oap.http.server.nio.HttpServerExchange;
 import oap.http.server.nio.NioHttpServer;
-import org.apache.http.entity.ContentType;
 
 @Slf4j
 public class PrometheusExporter implements HttpHandler {
     public static final PrometheusMeterRegistry prometheusRegistry = new PrometheusMeterRegistry( PrometheusConfig.DEFAULT );
+    private static long metricCount = 0L;
 
     static {
         Metrics.addRegistry( prometheusRegistry );
+
+        Metrics.gauge( "system_metrics_total", prometheusRegistry, pmr -> metricCount );
     }
 
     public PrometheusExporter( NioHttpServer server ) {
@@ -51,7 +54,19 @@ public PrometheusExporter( NioHttpServer server, String port ) {
 
     @Override
     public void handleRequest( HttpServerExchange exchange ) throws Exception {
+        metricCount = getMetricCount();
+
         var response = prometheusRegistry.scrape();
-        exchange.responseOk( response, ContentType.TEXT_PLAIN.getMimeType() );
+        exchange.responseOk( response, TextFormat.CONTENT_TYPE_004 );
+    }
+
+    private static long getMetricCount() {
+        long count = 0;
+        var en = prometheusRegistry.getPrometheusRegistry().metricFamilySamples();
+        while( en.hasMoreElements() ) {
+            var s = en.nextElement();
+            count += s.samples.size();
+        }
+        return count;
     }
 }

pom.xml

@@ -46,7 +46,7 @@
     </repositories>
 
     <properties>
-        <oap.project.version>21.3.3</oap.project.version>
+        <oap.project.version>21.3.4</oap.project.version>
 
         <oap.deps.config.version>21.0.0</oap.deps.config.version>