The [Prometheus] monitoring tool follows a white-box monitoring approach: Applications actively provide metrics about their internal state, and the Prometheus server pulls these metrics from the applications using HTTP.

If you can modify the application’s source code, it is straightforward to instrument an application with Prometheus metrics: Add the Prometheus client library as a dependency, call that library to maintain the metrics, and use the library to expose the metrics via HTTP.

However, DevOps teams do not always have the option to modify the source code of the applications they are running.

At this year’s [JavaZone] conference, Fabian Stäber did a [talk] on how to instrument Java Web Applications with Prometheus metrics without modifying the application’s source code.

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