Artemis Prometheus Metrics Plugin

This is a metrics plugin implementation for the ActiveMQ Artemis message broker. It provides integration with Prometheus using two modules:

artemis-prometheus-metrics-plugin Provides the actual implementation of org.apache.activemq.artemis.core.server.metrics.ActiveMQMetricsPlugin and packages it with the micrometer and Prometheus dependencies in an "uber" jar.
artemis-prometheus-metrics-plugin-servlet Provides a war file containing a simple servlet which can be deployed to the broker's embedded web server which then Prometheus can use to scrape metrics.

Building

Simply run mvn install. This command will build both modules and the output will be in their respective target directories.

After building the artifacts follow these steps:

Copy artemis-prometheus-metrics-plugin/target/artemis-prometheus-metrics-plugin-<VERSION>.jar to <ARTEMIS_INSTANCE>/lib.

Add this to your <ARTEMIS_INSTANCE>/etc/broker.xml:

<metrics><plugin class-name="org.apache.activemq.artemis.core.server.metrics.plugins.ArtemisPrometheusMetricsPlugin"/></metrics>

Create the directory <ARTEMIS_INSTANCE>/web.
Copy artemis-prometheus-metrics-plugin-servlet/target/metrics.war to <ARTEMIS_INSTANCE>/web.
Add this to the web element in <ARTEMIS_INSTANCE>/etc/bootstrap.xml:
```
<app url="metrics" war="metrics.war"/>
```