feat(serializers.prometheusremotewrite): Log metric conversion errors

[hagen1778]

With this change, prometheusremotewrite will log the last recorded conversion error in SerializeBatch

Summary

If the configured input contains bad data, then user might not be aware of the parsing errors as telegraf won't emit any logs or error messages. The error might be helpful for user to understand why some of the series were dropped during processing. In the same time, logging only the last error should prevent logs from pollution if too many conversion errors are taking place.

Checklist

• No AI generated code was used in this PR

Related issues

Resolves #15782

[srebhan]

@hagen1778 thanks a lot for your contribution! I have two comments in the code. Furthermore, I'm interested to learn why you do not log all errors but instead keep only the last error? What is the reasoning behind this?

[hagen1778]

Thanks for the quick review!

I'm interested to learn why you do not log all errors but instead keep only the last error? What is the reasoning behind this?

It is expected that metrics batch can contain errors in each series. So depending on the batch size and processing, telegraf could log a lot of errors and confuse the user.
On the other hand, printing one error log per batch still gives a hint to the user that something is wrong and gives enough information to act on. It should work effectively if metrics batch contains only one bad metric and many bad metrics. In both cases, error message can be used in order to get insights about invalid data.

[srebhan]

Thanks @hagen1778 for your update! I understand that you've chosen the last error as this simplifies the code. Could you please add this as a comment to the code so that the next reader doesn't wonder again? ;-)

Furthermore, would it be an option to log all errors with the Trace log level for people that want to see what is failing? Otherwise they will need to reproduce the scenario very often if there are a number of metrics failing...

[hagen1778]

@srebhan I've updated PR with your recommendations. I'd appreciate you taking another look.

[srebhan]

Thanks @hagen1778! I will adapt the wording in the README a bit but otherwise the PR looks good.

[telegraf-tiger]

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz