Programmatic access to metrics - repositories, max timer, max event

[Noble Numbat <no...@gmail.com>]

Hi all

Thanks for the clarification in post ‘Adding metrics to Prometheus
endpoint in the API’ -  max_timer_driven_threads and
max_event_driven_threads are constants and at this stage we are
looking to expose them (and a few others below) to get better
programmatic access to NiFi monitoring. But getting access to them is
a challenge.

Tried:
The object passed to the PrometheusReportingTask’s onTrigger method
[1] is a StandardReportingContext [2] and this class has a
FlowController instance that contains the thread and repository
information we need. I tried to cast it to a StandardReportingContext
so I could access the information but got a
java.lang.ClassCastException, which I believe is caused by classes
loaded with different classLoaders, stack trace below [3].

I tried to resolve this by adding the file
org.apache.nifi.controller.reporting.ReportingContext under the local
META-INF.services [4] to force the classLoader to load both classes,
but same error.

Question:
How would you suggest accessing the maxTimerDrivenThreads,
maxEventDrivenThreads, contentRepository, flowFileRepository and
provenanceRepository fields that are available via the FlowController
instance that’s in StandardReportingContext [2]?

thanks

[1] https://github.com/apache/nifi/blob/main/nifi-nar-bundles/nifi-prometheus-bundle/nifi-prometheus-reporting-task/src/main/java/org/apache/nifi/reporting/prometheus/PrometheusReportingTask.java#L196

[2] https://github.com/apache/nifi/blob/main/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/java/org/apache/nifi/controller/reporting/StandardReportingContext.java

[3] 2021-02-12 11:15:29,434 ERROR [Timer-Driven Process Thread-3]
o.a.n.r.p.PrometheusReportingTask
PrometheusReportingTask[id=938b946e-0177-1000-221f-68f6ba8694a6] :
java.lang.ClassCastException:
org.apache.nifi.controller.reporting.StandardReportingContext cannot
be cast to org.apache.nifi.controller.reporting.StandardReportingContext
java.lang.ClassCastException:
org.apache.nifi.controller.reporting.StandardReportingContext cannot
be cast to org.apache.nifi.controller.reporting.StandardReportingContext
at org.apache.nifi.reporting.prometheus.PrometheusReportingTask.onTrigger(PrometheusReportingTask.java:296)
at org.apache.nifi.controller.tasks.ReportingTaskWrapper.run(ReportingTaskWrapper.java:44)
at org.apache.nifi.engine.FlowEngine$2.run(FlowEngine.java:110)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

[4] https://github.com/apache/nifi/blob/main/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core/src/main/resources/META-INF/services