balancer: expose endpoint weight and hostname as experimental APIs by hpathak01 · Pull Request #9074 · grpc/grpc-go

hpathak01 · 2026-04-17T08:34:02Z

Description

This PR exposes two new experimental public APIs so that custom load balancing policies can access endpoint attributes that were previously only available via internal packages:

google.golang.org/grpc/balancer/weight — Set, FromEndpoint, EndpointInfo
google.golang.org/grpc/balancer/hostname — Set, FromEndpoint, FromAddress

These attributes (especially weight) are required by custom balancers such as deterministic aperture / P2C that need EDS-provided endpoint details like weights etc.

Changes

New public package balancer/hostname with full experimental notices.
Moved internal/balancer/weight to public balancer/weight via git mv, added experimental notices.
Internal callers (ringhash, pickfirst, cdsbalancer, clusterimpl, xdsresource) updated to use the public packages directly.
Removed SetHostname and Hostname wrappers from xdsresource; callers now use hostname.Set and hostname.FromAddress directly.
Added table-driven unit tests for both new public packages.

Related Issues

Fixes #8971

Testing

All tests pass (go test -count=1 ./...)

Notes for Reviewers

The new APIs follow the exact same experimental pattern used by resolver/ringhash.
The "Dependency Changes" check fails because this PR intentionally adds two new public packages (balancer/weight and balancer/hostname).

RELEASE NOTES: none

linux-foundation-easycla · 2026-04-17T08:34:10Z

The committers listed above are authorized under a signed CLA.

✅ login: hpathak01 / name: Harsh Pathak (0132067, 1b58d32, 3b06903, 5ed3447, 777e7f6, 83417df, 9fa484c, cad2a5f, d39465e, f30c259)

codecov · 2026-04-17T08:37:17Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.09%. Comparing base (06fc26a) to head (f30c259).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9074      +/-   ##
==========================================
+ Coverage   80.52%   83.09%   +2.56%     
==========================================
  Files         413      414       +1     
  Lines       33543    33480      -63     
==========================================
+ Hits        27012    27819     +807     
+ Misses       4316     4236      -80     
+ Partials     2215     1425     -790

Files with missing lines	Coverage Δ
balancer/hostname/hostname.go	`100.00% <100.00%> (ø)`
balancer/pickfirst/pickfirst.go	`89.28% <ø> (-0.48%)`	⬇️
balancer/ringhash/ringhash.go	`94.11% <ø> (ø)`
balancer/weight/weight.go	`100.00% <ø> (ø)`
internal/xds/balancer/cdsbalancer/configbuilder.go	`91.11% <100.00%> (ø)`
internal/xds/balancer/clusterimpl/clusterimpl.go	`88.25% <100.00%> (ø)`
...nternal/xds/xdsclient/xdsresource/unmarshal_eds.go	`96.00% <100.00%> (+4.22%)`	⬆️

... and 32 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

…rpc#8971) - Add new public packages balancer/weight and balancer/hostname with Set/FromEndpoint and Set/Hostname/HostnameFromAddress helpers. - Mark all new APIs as # Experimental with the standard notice. - Update internal callers (ringhash, pickfirst, cdsbalancer, xdsresource) to use the public packages. - Remove dead hostnameKeyType from xdsresource and delegate legacy Hostname() to the public API (fixes Authority_Rewrite_Mismatch test). - Keep deprecated internal/balancer/weight package for transition. - Add tests for the new public packages. - Verified end-to-end with custom DAPerture balancer.

easwars · 2026-04-20T05:26:02Z

The "Dependency Changes" check fails because this PR intentionally adds two new public packages (balancer/weight and balancer/hostname).

Yes, that is expected.

easwars · 2026-04-20T05:26:24Z

@Pranjali-2501 : Could you please do a first pass.

Pranjali-2501

Hi @hpathak01, thanks for raising the PR.
I have added some comments, please take a look.

Pranjali-2501 · 2026-04-21T07:41:09Z

+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func Hostname(endpoint resolver.Endpoint) string {


I think it will be better to rename it as FromEndpoint.

Pranjali-2501 · 2026-04-21T07:41:25Z

+	return h
+}
+
+// FromAddress returns the hostname attribute from a legacy


We don't need to export the function to retrieve hostname from address.attributes and address.BalancerAttributes.
Please remove this.

Pranjali-2501 · 2026-04-21T07:41:46Z

 	"time"

 	"github.com/google/go-cmp/cmp"
+


Remove this new line.

Pranjali-2501 · 2026-04-21T07:42:04Z

 // Package weight contains utilities to manage endpoint weights. Weights are
 // used by LB policies such as ringhash to distribute load across multiple
 // endpoints.
+//


Instead of putting a deprecated message and creating new files in balancer/weight/, use git move to move the files from internal/balancer/weight/weight.go to balancer/weight/weight.go.

done - i also added the "Experimental" comment because this is a newly-public API. is that fine?

Pranjali-2501 · 2026-04-21T07:42:08Z

 *
 */

+// Deprecated: use google.golang.org/grpc/balancer/weight instead.


Same as above, use git move to move this file also.

Pranjali-2501 · 2026-04-21T07:42:12Z

 	"time"

 	"github.com/google/go-cmp/cmp"
+


Please remove this newline.

Pranjali-2501 · 2026-04-21T07:42:24Z

-	}
-	endpoint.Attributes = endpoint.Attributes.WithValue(hostnameKeyType{}, hostname)
-	return endpoint
+func SetHostname(endpoint resolver.Endpoint, h string) resolver.Endpoint {


We don't need to call exported Get/Set function from another function. Directly use hostname.Set whenever required.

Pranjali-2501 · 2026-04-21T07:42:31Z

-// Address. If this attribute is not set, it returns the empty string.
+// Hostname returns the hostname from the given legacy Address.
+// If this attribute is not set, it returns the empty string.
 func Hostname(addr resolver.Address) string {


Please revert the changes made in this function. We have an exported function to set hostname in endpoint. And will keep the function internal to retrieve the hostname resolver.Address.

hi @Pranjali-2501 reverting this function causes two issues:

The original hostnameKeyType has been removed above, so it wouldn't compile.

Even if we bring hostnameKeyType back, the test TestAuthorityOverridingWithTLS/Authority_Rewrite_Mismatch fails — because EDS unmarshal now writes hostname via hostname.Set (which uses the hostnameKey defined in balancer/hostname/hostname.go), but the original Hostname(addr) would read with its own internal key type, so the hostname is never found.

The current implementation delegates to hostname.FromEndpoint so both setter and getter use the same key. All tests pass. Does this approach work, or would you prefer a different solution?

IMO, the best way will be to move this function to balancer/hostname/hostname.go, export it and name it FromAddress.

Pranjali-2501 · 2026-04-22T06:24:04Z

-// Address. If this attribute is not set, it returns the empty string.
+// Hostname returns the hostname from the given legacy Address.
+// If this attribute is not set, it returns the empty string.
 func Hostname(addr resolver.Address) string {


IMO, the best way will be to move this function to balancer/hostname/hostname.go, export it and name it FromAddress.

Pranjali-2501 · 2026-04-22T06:44:05Z

@hpathak01 , please fix Testing / static checks (latest-1) (pull_request).

hpathak01 · 2026-04-22T07:38:30Z

@hpathak01 , please fix Testing / static checks (latest-1) (pull_request).

hi @Pranjali-2501 done

Pranjali-2501

LGTM.

Pranjali-2501 · 2026-04-23T05:03:39Z

+	return endpoint
+}
+
+// FromEndpoint returns the hostname attribute of endpoint. If this attribute is


nit: wrap the comment in 80 columns.

hpathak01 · 2026-05-06T03:58:41Z

Hi @easwars , just checking in — I've addressed all the review comments. Would you have a chance to take a look when you get a moment? Thanks!

hpathak01 force-pushed the hpathak01/issue-8971-expose-xds-attr branch from 7e7f078 to 5ed3447 Compare April 17, 2026 08:39

hpathak01 added 3 commits April 17, 2026 16:52

[balancer] fix import ordering in test and xdsresource files

d39465e

[ci] fix import ordering for goimports check

83417df

[ci] run goimports on all changed files

1b58d32

hpathak01 marked this pull request as ready for review April 20, 2026 03:45

easwars added the Type: Feature New features or improvements in behavior label Apr 20, 2026

easwars added this to the 1.82 Release milestone Apr 20, 2026

easwars added the Area: Resolvers/Balancers Includes LB policy & NR APIs, resolver/balancer/picker wrappers, LB policy impls and utilities. label Apr 20, 2026

easwars changed the title ~~[balancer] expose endpoint weight and hostname as experimental APIs (…~~ balancer: expose endpoint weight and hostname as experimental APIs Apr 20, 2026

easwars requested a review from Pranjali-2501 April 20, 2026 05:26

easwars assigned Pranjali-2501 Apr 20, 2026

Pranjali-2501 reviewed Apr 21, 2026

View reviewed changes

Pranjali-2501 assigned hpathak01 and unassigned Pranjali-2501 Apr 21, 2026

Pranjali-2501 added the Status: Requires Reporter Clarification label Apr 21, 2026

hpathak01 added 3 commits April 21, 2026 17:38

balancer: address review comments for weight/hostname APIs

0132067

balancer: address review comments for weight/hostname APIs (2)

3b06903

balancer: remove empty line in import

cad2a5f

Pranjali-2501 reviewed Apr 22, 2026

View reviewed changes

hpathak01 added 2 commits April 22, 2026 15:09

balancer: review comments addressed

9fa484c

balancer: revert unintentional import change

777e7f6

Pranjali-2501 approved these changes Apr 23, 2026

View reviewed changes

Pranjali-2501 reviewed Apr 23, 2026

View reviewed changes

Pranjali-2501 assigned easwars and unassigned hpathak01 Apr 23, 2026

Pranjali-2501 requested a review from easwars April 23, 2026 05:04

balancer/hostname: wrap doc comment at 80 cols

f30c259

Pranjali-2501 removed the Status: Requires Reporter Clarification label Apr 27, 2026

Conversation

hpathak01 commented Apr 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Changes

Related Issues

Testing

Notes for Reviewers

Uh oh!

linux-foundation-easycla Bot commented Apr 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

codecov Bot commented Apr 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

easwars commented Apr 20, 2026

Uh oh!

easwars commented Apr 20, 2026

Uh oh!

Pranjali-2501 left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Pranjali-2501 commented Apr 22, 2026

Uh oh!

hpathak01 commented Apr 22, 2026

Uh oh!

Pranjali-2501 left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

hpathak01 commented May 6, 2026

Uh oh!

Reviewers

Assignees

Labels

hpathak01 commented Apr 17, 2026 •

edited

Loading

linux-foundation-easycla Bot commented Apr 17, 2026 •

edited

Loading

codecov Bot commented Apr 17, 2026 •

edited

Loading