Enable reactor netty metrics (#124)

Signed-off-by: Seddik Yengui <[email protected]>

Author: YenguiSeddik

pom.xml

@@ -110,6 +110,10 @@
             <groupId>org.springframework.cloud</groupId>
             <artifactId>spring-cloud-starter-gateway</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.micrometer</groupId>
+            <artifactId>micrometer-core</artifactId>
+        </dependency>
 
         <!-- runtime dependencies -->
         <dependency>

src/main/java/org/gridsuite/gateway/NettyMetricsConfiguration.java

@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2024, RTE (http://www.rte-france.com)
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+package org.gridsuite.gateway;
+
+import io.micrometer.core.instrument.config.MeterFilter;
+import org.springframework.boot.web.embedded.netty.NettyServerCustomizer;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import reactor.netty.http.server.HttpServer;
+
+import java.util.List;
+import java.util.function.Function;
+
+/**
+ * @author Seddik Yengui <seddik.yengui_externe at rte-france.com>
+ */
+
+// Enable Netty metrics that are not enabled by default in Spring Boot.
+@Configuration
+public class NettyMetricsConfiguration implements NettyServerCustomizer {
+
+    private static final String REACTOR_NETTY_PREFIX = "reactor.netty";
+    // If additional metrics are added, ensure the URIs are provided in a template-like format.
+    // Without this, each unique URI generates a separate tag, which takes a lot of memory
+    private static final List<String> ALLOWED_REACTOR_NETTY_METRICS = List.of(
+            "reactor.netty.http.server.connections.total",
+            "reactor.netty.http.server.connections.active"
+    );
+
+    @Override
+    public HttpServer apply(HttpServer httpServer) {
+        return httpServer.metrics(true, Function.identity());
+    }
+
+    @Bean
+    public MeterFilter meterFilter() {
+        return MeterFilter.denyUnless(id -> {
+            String name = id.getName();
+            // Allow all non-reactor metrics
+            if (!name.startsWith(REACTOR_NETTY_PREFIX)) {
+                return true;
+            }
+            // Allow only the specific reactor metrics that we use
+            return ALLOWED_REACTOR_NETTY_METRICS.contains(name);
+        });
+    }
+}