By setting up Apache Druid to push the metrics to a HTTP service, you are able to collect metrics for monitoring. This service exposes only two endpoints:
/collect/metrics
This endpoint is a POST where you can instruct Druid to send the metrics to. The endpoint will parse each feed and update the corresponded prometheus metric.
The prometheus client exposes all the metrics on this endpoint. In this way, your prometheus server can read the exposed metrics.
You need to configure Druid to send the metrics to this service. To do so,you need to change the configuration file to add/update it with the following entries
druid_emitter_logging_logLevel=debug
druid_emitter_logging_loggerClass=HttpPostEmitter
druid_emitter=http
druid_emitter_http_recipientBaseUrl=http://{exporter_addr}:7000/collect
In the config folder of this project, you can find an example.