micrometer-metrics/micrometer

Statsd UDP epoll warn logs are verbose when statsd down

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#2,624 opened on May 27, 2021

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help wantedregistry: statsdtype: task

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Description

Testing on Linux, I can see we get logs like the following with #2611 (and therefore epoll enabled) when the statsd daemon isn't running:

2021-05-28 03:11:45.544  WARN 6373 --- [    udp-epoll-1] i.m.s.reactor.netty.channel.FluxReceive  : [id:35f314ec, L:/127.0.0.1:60434 - R:localhost/127.0.0.1:8125] An exception has been observed post termination, use DEBUG level to see the full stack: java.net.PortUnreachableException: readAddress(..) failed: Connection refused
2021-05-28 03:11:45.554  WARN 6373 --- [    udp-epoll-1] i.m.s.reactor.netty.channel.FluxReceive  : [id:35f314ec, L:/127.0.0.1:60434 - R:localhost/127.0.0.1:8125] An exception has been observed post termination, use DEBUG level to see the full stack: java.net.PortUnreachableException: readAddress(..) failed: Connection refused

This is a bit verbose compared to without epoll enabled, in this scenario of the statsd daemon being down. With epoll enabled and the statsd daemon running, metrics are received and no logs are output, as expected.

Originally posted by @shakuzen in https://github.com/micrometer-metrics/micrometer/pull/2611#issuecomment-849839027

Contributor guide

Research direction
Investigate the epoll UDP handling in Reactor Netty's FluxReceive to find why PortUnreachableException is logged at WARN level and propose a change to reduce verbosity (e.g., log at DEBUG or handle silently).
Tech stack
java
Domain
backendobservability
Issue type
Bug
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3
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Prerequisites
JavaReactor Netty
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40