ringhash: move out of the xds package

[atollena]

fixes #8213

There is a new API in that ring hash can now be used by importing google.golang.org/grpc/balancer/ringhash
instead of importing all of google.golang.org/grpc/xds.

RELEASE NOTES:

• balancer/ringhash: move LB policy from xds/internal to exported path

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.16%. Comparing base (7d68bf6) to head (9b037a8).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8249      +/-   ##
==========================================
+ Coverage   82.02%   82.16%   +0.13%     
==========================================
  Files         412      412              
  Lines       40477    40477              
==========================================
+ Hits        33201    33256      +55     
+ Misses       5897     5864      -33     
+ Partials     1379     1357      -22     

Files with missing lines	Coverage Δ
balancer/ringhash/config.go	92.30% <100.00%> (ø)
balancer/ringhash/logging.go	100.00% <ø> (ø)
balancer/ringhash/picker.go	96.61% <100.00%> (ø)
balancer/ringhash/ring.go	100.00% <ø> (ø)
balancer/ringhash/ringhash.go	94.22% <100.00%> (ø)
internal/ringhash/ringhash.go	100.00% <ø> (ø)
xds/internal/resolver/serviceconfig.go	85.71% <100.00%> (ø)
...nal/xdsclient/xdslbregistry/converter/converter.go	70.62% <100.00%> (ø)

... and 27 files with indirect coverage changes

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[arjan-bal]

This test failure is in a new ringhash test, but probably not related to this PR: https://github.com/grpc/grpc-go/actions/runs/14454284376/job/40533854683?pr=8249

[arjan-bal]

LGTM, adding a second reviewer.

[dfawley]

Please move this package under an internal directory. Or can we move it into the parent directory and just put it in the ringhash_test package?

[atollena]

Done.

[dfawley]

Curious: is setting the xds request hash something that anyone else would need to be able to do? E.g. for testing? I'm fine with leaving this as-is for now, but I'm also OK with making that functionality public if we think it might be needed.

[atollena]

The main problem here is a cross-language concern raised by Mark: see grpc/grpc#33356 (comment):

However, I am a little concerned about the complexity involved in exposing an interface to programmatically set the request's hash. When we discussed this earlier, we were thinking that this would probably just be something simple like "use a specific request header", which could just be built into the ring_hash policy. Exposing an API to allow applications to do this programmatically is a much broader API surface, and before going down that road, I'd like to be convinced that there's no simpler way to do this. Is there a way that we can handle your use-case without that complexity?

So I think that unless we are willing to provide functionalities that may not be available in other languages, it's better to limit the visibility to the xds use case.

[dfawley]

SG. Sounds like users won't need to be able to set it this way for any testing, either, so let's keep it as is.

[dfawley]

Thanks!