Exporter is not available after restarting PrometheusTelemetry

[janpieper]

When starting PrometheusTelemetry it does a :persistent_term.put/2:

prometheus_telemetry_elixir/lib/prometheus_telemetry.ex

Line 149 in 1dbd353

:persistent_term.put(@exporter_enabled_key, [port | :persistent_term.get(@exporter_enabled_key, [])])

But there is currently no way to correctly stop it again. When using Supervisor.stop(pid) it stops the supervisor, but the :persistent_term key won't be updated. So, when restarting PrometheusTelemetry, the :__exporter_ports__ still contains the port that is not used anymore, which prohibits starting the exporter again.

Before restaring PrometheusTelemetry, we currently need to do this:

Supervisor.stop(pid)
:persistent_term.put(:__exporter_ports__, :persistent_term.get(:__exporter_ports__) -- [port])

Would be cool to have a stop function for this which takes care about removing the port from the persistent term.

[MikaAK]

I'm curious what use case causes the exporter to need restarting. Great find though!

[janpieper]

I have tests for my custom metrics. When doing something 10-times, I expect my metric to be set to 10.

To reset the metrics for each test, I need to restart PrometheusMetrics.

[MikaAK]

Probably just need to hook into termination and flag it for the supervisor to do cleanup, I will take a look at getting this in soon