feat(prometheus): Add native /metrics endpoint

activemq-prometheus/README.md

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+<!--
+    Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+-->
+
+# ActiveMQ Prometheus Metrics
+
+## Activation
+
+1. Uncomment the `Prometheus Metrics Web Application` block from `conf/jetty/jetty-webapps.xml`.
+2. Restart the broker
+
+The endpoint uses the existing Jetty management listener, TLS configuration,
+IP allowlist, and JAAS realm. Its path is restricted to the `admins` role
+but can be changed in `conf/jetty/jetty-security.xml`.
+
+## Endpoints
+
+Two endpoints because brokers with many destinations might produce large responses:
+- `GET /metrics`: broker-level metrics only.
+- `GET /metrics?per_object=true`: per-queue, per-topic, and broker-level metrics
+
+## Metrics
+
+### Broker metrics (`activemq_broker_*`)
+
+| Metric | Type | Description |
+|--------|------|-------------|
+| `connections` | gauge | Current number of connections |
+| `connections_total` | counter | Total connections since last start |
+| `messages_enqueued_total` | counter | Total messages enqueued since last start |
+| `messages_dequeued_total` | counter | Total messages dequeued since last start |
+| `consumers` | gauge | Current number of consumers |
+| `producers` | gauge | Current number of producers |
+| `messages` | gauge | Current number of messages across all destinations |
+| `memory_percent_usage` | gauge | Percent of memory limit used |
+| `memory_limit_bytes` | gauge | Memory limit in bytes |
+| `store_percent_usage` | gauge | Percent of store limit used |
+| `store_limit_bytes` | gauge | Store limit in bytes |
+| `temp_percent_usage` | gauge | Percent of temp limit used |
+| `temp_limit_bytes` | gauge | Temp limit in bytes |
+| `uptime_milliseconds` | gauge | Broker uptime in milliseconds |
+| `queues` | gauge | Number of queues on the broker |
+| `topics` | gauge | Number of topics on the broker |
+| `job_scheduler_store_percent_usage` | gauge | Percent of job scheduler store limit used |
+| `job_scheduler_store_limit_bytes` | gauge | Job scheduler store limit in bytes |
+
+### Destination metrics (`activemq_queue_*` / `activemq_topic_*`)
+
+Returned only when `?per_object=true` is set.
+
+| Metric | Type | Description |
+|--------|------|-------------|
+| `messages` | gauge | Number of messages in destination |
+| `enqueued_total` | counter | Total messages enqueued since last start |
+| `dequeued_total` | counter | Total messages dequeued since last start |
+| `dispatched_total` | counter | Total messages dispatched since last start |
+| `message_inflight_count` | gauge | Messages dispatched but not acknowledged |
+| `expired_total` | counter | Total messages expired since last start |
+| `consumers` | gauge | Number of consumers |
+| `producers` | gauge | Number of producers |
+| `memory_percent_usage` | gauge | Percent of destination memory limit used |
+| `memory_limit_bytes` | gauge | Memory limit for destination in bytes |
+| `memory_usage_bytes` | gauge | Memory used by destination in bytes |
+| `store_message_size_bytes` | gauge | Store message size in bytes |
+| `average_enqueue_time_milliseconds` | gauge | Average time (since last start) messages waited before dispatch |
+
+## Prometheus configuration
+
+Example yaml configuration for running a Prometheus scraper on the same machine as the broker
+```yaml
+scrape_configs:
+  - job_name: activemq
+    metrics_path: /metrics
+    params:
+      per_object: ['true']  # omit for broker-only
+    basic_auth:
+      username: admin
+      password: admin
+    static_configs:
+      - targets: ['localhost:8161']
+```

activemq-prometheus/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You under the Apache License, Version 2.0
+  (the "License"); you may not use this file except in compliance with
+  the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.apache.activemq</groupId>
+        <artifactId>activemq-parent</artifactId>
+        <version>6.4.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>activemq-prometheus</artifactId>
+    <packaging>war</packaging>
+    <name>ActiveMQ :: Prometheus</name>
+    <description>ActiveMQ Prometheus metrics endpoint</description>
+
+    <dependencies>
+
+        <!-- =============================== -->
+        <!-- Required Dependencies -->
+        <!-- =============================== -->
+        <dependency>
+            <groupId>jakarta.servlet</groupId>
+            <artifactId>jakarta.servlet-api</artifactId>
+            <scope>provided</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+        </dependency>
+
+        <!-- =============================== -->
+        <!-- Testing Dependencies            -->
+        <!-- =============================== -->
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>metrics</finalName>
+    </build>
+
+</project>