fix: modernize Ceph input plugin metrics

[G-regL]

Required for all PRs:

• Updated associated README.md.
• Wrote appropriate unit tests.
• Pull request title or commits are in conventional commit format

resolves #10788

The Ceph input plugin was likely written against version 11 or 12 of Ceph, but since then there's been some changes to the data structures that the respective ceph commands use for cluster-level statistics.

This PR aims to bring those values back inline with at least version 15 of Ceph.

[Hipska]

Great you are willing to modernise this input, but I have some doubts about backwards compatibility.

[reimda]

Hi Greg, could you rebase this on current master? CI isn't running on this branch. Rebasing will pull in the new circle ci config and should trigger CI to run again.

[reimda]

Thanks for merging master to get CI working.

I did a quick review of the PR and it's great that you've made it compatible with new versions of ceph. I'm concerned that it may break compatibility with older versions. Do you know if the PR will work with older versions?

It looks like the changes to the unit tests affect both input json and expected metrics. Could we leave the old test cases as they were to show the plugin still works when run with older ceph versions, and add new test cases to cover the new json format?

[reimda]

Hi @G-regL, were you able to look into compatibility with older versions of Ceph?

[G-regL]

I hadn't looked at it since your previous comment, but in looking at it now, there's two unit tests, one which covers the old data for Cluster Status; clusterStatusDump, and cephStatusResults are for new data, while clusterStatusDumpNestedOSD, and cephStatusResultsNestedOSD are for old data.

Was there something more specific you were looking for cover?

[powersj]

I hadn't looked at it since your previous comment, but in looking at it now, there's two unit tests, one which covers the old data for Cluster Status; clusterStatusDump, and cephStatusResults are for new data, while clusterStatusDumpNestedOSD, and cephStatusResultsNestedOSD are for old data.

Was there something more specific you were looking for cover?

Looking at plugins/inputs/ceph/ceph_test.go there is a cephDFDump which has some sample JSON data in it for example. It no longer has some specific fields that were there previously. This tends to raise some concern if older test cases were changed without maintaining backward compatibility.

Should this change have been a new test case?

Thanks - trying to ensure we aren't suddenly breaking existing users as Dave pointed out.

[powersj]

Given version 16 of Ceph is currently the oldest version of ceph now supported, I'm going to retract my questions about tests.

@G-regL - if you could update the PR with some of our recent changes to the sample config and build tags we can look to getting this added.

[G-regL]

I can certainly update the sample config, but I don't quite know what you mean with regards to the build tags.

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_amd64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

☺️ This pull request doesn't significantly change the Telegraf binary size (less than 1%)

📦 Click here to get additional PR build artifacts

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_i386.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz
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
		static_linux_amd64.tar.gz

[powersj]

Thanks

[srebhan]

Looks good to me. Thanks for all your effort @G-regL!