plugin/kubernetes: Add useragent

[mrueg]

1. Why is this pull request needed and what does it do?

CoreDNS doesn't set a UserAgent and client-go will fallback to the default one https://github.com/kubernetes/client-go/blob/master/rest/config.go#L498

In kubernetes' audit logs you'll see:

"userAgent":"coredns/v0.0.0 (linux/amd64) kubernetes/$Format"

This change adds a userAgent to the requests made by CoreDNS against the kubernetes API:

"userAgent":"CoreDNS/v1.11.1+ae2bbc29be1aaae0b3ded5d188968a6c97bb3144 (linux/amd64)"

2. Which issues (if any) are related?

3. Which documentation changes (if any) need to be made?

4. Does this introduce a backward incompatible change or deprecation?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 59.22%. Comparing base (93c57b6) to head (35578b2).
Report is 1184 commits behind head on master.

Files	Patch %	Lines
plugin/kubernetes/kubernetes.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6484      +/-   ##
==========================================
+ Coverage   55.70%   59.22%   +3.52%     
==========================================
  Files         224      252      +28     
  Lines       10016    13473    +3457     
==========================================
+ Hits         5579     7979    +2400     
- Misses       3978     4902     +924     
- Partials      459      592     +133     

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[SuperQ]

I like it, minor nit about formatting.

Also, what about including runtime.Version() so we know what compiler version was used?

[mrueg]

I like it, minor nit about formatting.

Also, what about including runtime.Version() so we know what compiler version was used?

Sure we can add it, not sure if the compiled golang version provides any additional value here?

[SuperQ]

Usually when trying to identify a build, I like to have as much unique info as possible. I also usually like to include the git branch name. Looks like we don't have this in the current coremain package.

[chrisohaver]

Have the comments been addressed? Not sure since commits were squashed.

[mrueg]

I haven't addressed the comments yet.
I can change the format of the useragent to state git_commit explicitly.
I'm still torn a bit about exposing runtime.Version() in the useragent. Any thoughts on this @chrisohaver ?

[chrisohaver]

I'm still torn a bit about exposing runtime.Version() in the useragent. Any thoughts on this @chrisohaver ?

What's an example of how it could be useful?

[mrueg]

I'm still torn a bit about exposing runtime.Version() in the useragent. Any thoughts on this @chrisohaver ?

What's an example of how it could be useful?

I don't have one (and I would favor not exposing it). @SuperQ any thoughts why you would need this?

[mrueg]

@SuperQ @chrisohaver anything else I need to do before this is ready to be merged?

[SuperQ]

Having the compiler version can be useful in finding bugs/security issues.

[mrueg]

Having the compiler version can be useful in finding bugs/security issues.

Wouldn't you rather rely on container scanning or similar for that? I think the purpose of a useragent is to help identifying the client and not to provide extended metadata (because right now it says kubernetes, which is misleading).

[SuperQ]

Scanners are solving a different issue. This is about having the context inline at the time of use.

[mrueg]

I've included the runtime.Version(), I personally still lack the benefit but eventually rather have a few bytes more in my log storage system than having trying to guess which coredns version logged it. :)

This is what it will look like now:

"userAgent":"CoreDNS/v1.11.1 git_commit:ae2bbc29be1aaae0b3ded5d188968a6c97bb3144 (linux/amd64/go1.22)"

[SuperQ]

Great!