bugfix: even no endpoints left after filter, an empty object should be returned to clients

[rambohe-ch]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage

/kind bug

What this PR does / why we need it:

if no endpoints left after service topology filtering, yurthub should return a empty endpointslice to clients(like kube-proxy) instead of skipping the object. because kube-proxy need to use the empty endpointslice to update network setting on edge nodes.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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In response to this:

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage

/kind bug

What this PR does / why we need it:

if no endpoints left after service topology filtering, yurthub should return a empty endpointslice to clients(like kube-proxy) instead of skipping the object. because kube-proxy need to use the empty endpointslice to update network setting on edge nodes.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rambohe-ch

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• OWNERS [rambohe-ch]

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[rambohe-ch]

@zzguang @yingjianjian PTAL

[codecov]

Codecov Report

Merging #1028 (16d281c) into master (cd00f26) will increase coverage by 0.20%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1028      +/-   ##
==========================================
+ Coverage   47.74%   47.94%   +0.20%     
==========================================
  Files          95       95              
  Lines       13013    12970      -43     
==========================================
+ Hits         6213     6219       +6     
+ Misses       6266     6216      -50     
- Partials      534      535       +1     

Flag	Coverage Δ
unittests	47.94% <66.66%> (+0.20%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/yurthub/filter/servicetopology/handler.go	74.75% <66.66%> (+15.31%)	⬆️

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[Congrool]

/lgtm

[rambohe-ch]

/backport release-v1.0

[rambohe-ch]

/backport release-v1.0

[github-actions]

Successfully created backport PR #1030 for release-v1.0.