From 58eca0c2195e7b59cf683459dee3296e40c9a5e0 Mon Sep 17 00:00:00 2001
From: hujincalrin41 <hujincalrin41@gmail.com>
Date: Mon, 13 Jul 2026 08:47:01 +0000
Subject: [PATCH] feat: expose Prometheus metrics at /metrics

Wire Armeria's built-in MetricCollectingService into a Prometheus meter registry
and serve it via PrometheusExpositionService at /metrics, so per-route request
counts (e.g. generateTemporaryTableCredential) are scrapeable. Adds the
micrometer-registry-prometheus dependency; no change to existing routes/handlers.

Verified locally: /metrics returns 200 and
armeria_server_requests_total{method="generateTemporaryTableCredential"}
increments per request.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 build.sbt                                         |  2 ++
 .../unitycatalog/server/UnityCatalogServer.java   | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/build.sbt b/build.sbt
index 82c859d..359d63a 100644
--- a/build.sbt
+++ b/build.sbt
@@ -328,6 +328,8 @@ lazy val server = (project in file("server"))
     ) ++ javacRelease17,
     libraryDependencies ++= Seq(
       "com.linecorp.armeria" %  "armeria" % "1.28.4",
+      // Prometheus registry for armeria's MetricCollectingService + /metrics exposition.
+      "io.micrometer" % "micrometer-registry-prometheus" % "1.12.4",
       "org.apache.commons" % "commons-lang3" % "3.19.0",
 
       // Netty dependencies
diff --git a/server/src/main/java/io/unitycatalog/server/UnityCatalogServer.java b/server/src/main/java/io/unitycatalog/server/UnityCatalogServer.java
index 923c3f9..cd7b697 100644
--- a/server/src/main/java/io/unitycatalog/server/UnityCatalogServer.java
+++ b/server/src/main/java/io/unitycatalog/server/UnityCatalogServer.java
@@ -8,11 +8,16 @@
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 import com.linecorp.armeria.common.HttpResponse;
+import com.linecorp.armeria.common.metric.MeterIdPrefixFunction;
+import com.linecorp.armeria.common.metric.PrometheusMeterRegistries;
 import com.linecorp.armeria.server.Server;
 import com.linecorp.armeria.server.ServerBuilder;
 import com.linecorp.armeria.server.annotation.JacksonRequestConverterFunction;
 import com.linecorp.armeria.server.annotation.JacksonResponseConverterFunction;
 import com.linecorp.armeria.server.docs.DocService;
+import com.linecorp.armeria.server.metric.MetricCollectingService;
+import com.linecorp.armeria.server.metric.PrometheusExpositionService;
+import io.micrometer.prometheus.PrometheusMeterRegistry;
 import io.unitycatalog.server.auth.AllowingAuthorizer;
 import io.unitycatalog.server.auth.JCasbinAuthorizer;
 import io.unitycatalog.server.auth.UnityCatalogAuthorizer;
@@ -99,9 +104,19 @@ private void setDefaults(UnityCatalogServer.Builder unityCatalogServerBuilder) {
   }
 
   private Server initializeServer(UnityCatalogServer.Builder unityCatalogServerBuilder) {
+    // Expose Prometheus metrics at /metrics so per-route request counts (e.g.
+    // credential vending) are scrapeable. MetricCollectingService records every
+    // route; PrometheusExpositionService serves the registry.
+    PrometheusMeterRegistry meterRegistry = PrometheusMeterRegistries.newRegistry();
     ServerBuilder armeriaServerBuilder =
         Server.builder()
             .http(unityCatalogServerBuilder.port)
+            .meterRegistry(meterRegistry)
+            .decorator(
+                MetricCollectingService.newDecorator(
+                    MeterIdPrefixFunction.ofDefault("armeria.server")))
+            .service(
+                "/metrics", PrometheusExpositionService.of(meterRegistry.getPrometheusRegistry()))
             .serviceUnder("/docs", new DocService());
 
     // Init hibernate