xds/clusterresolver: implement gRFC A61 changes for LOGICAL_DNS clusters by Pranjali-2501 · Pull Request #8733 · grpc/grpc-go

Pranjali-2501 · 2025-12-01T14:58:50Z

Fixes : #8153

This PR implements the "Changes to Logical DNS Clusters" section of gRFC A61 (IPv4/IPv6 Dual-stack Backends).

Currently, LOGICAL_DNS clusters in the xDS cluster resolver have their Load Balancing policy hard-coded to pick_first. This ensures the semantics of connecting to only one address at a time.

This PR updates the xds_cluster_resolver logic. The buildClusterImplConfigForDNS function removes the hard-coded pick_first policy restriction for LOGICAL_DNS clusters, allowing them to use the configured LB policy.
Also, in the DNS update handler, all resolved addresses are now grouped into a single resolver.Endpoint. This ensures that regardless of the configured parent LB policy, the child policy sees a single "backend" endpoint containing all addresses.

RELEASE NOTES:

xds: LOGICAL_DNS clusters now honor the LB policy configured in the cluster resource, rather than defaulting to a hardcoded pick_first policy.

codecov · 2025-12-01T15:02:12Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.35%. Comparing base (830c909) to head (41ff069).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8733      +/-   ##
==========================================
- Coverage   83.42%   83.35%   -0.07%     
==========================================
  Files         414      414              
  Lines       32751    32754       +3     
==========================================
- Hits        27322    27302      -20     
- Misses       4040     4057      +17     
- Partials     1389     1395       +6

Files with missing lines	Coverage Δ
...rnal/xds/balancer/clusterresolver/configbuilder.go	`92.59% <100.00%> (+0.16%)`	⬆️

... and 17 files with indirect coverage changes

🚀 New features to boost your workflow:

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

internal/xds/balancer/clusterresolver/resource_resolver_dns.go

internal/xds/balancer/clusterresolver/configbuilder.go

easwars · 2025-12-01T19:41:23Z

This change probably needs a release note.

internal/xds/balancer/clusterresolver/configbuilder.go

internal/xds/balancer/clusterresolver/configbuilder_test.go

internal/xds/balancer/clusterresolver/e2e_test/dns_impl_test.go

internal/xds/balancer/cdsbalancer/e2e_test/dns_impl_test.go

internal/xds/balancer/clusterresolver/configbuilder.go

internal/xds/balancer/clusterresolver/configbuilder_test.go

easwars · 2026-01-22T04:18:54Z

internal/xds/balancer/clusterresolver/configbuilder.go

+	localityStr := xdsinternal.LocalityString(clients.Locality{})
+	retEndpoint = hierarchy.SetInEndpoint(retEndpoint, []string{pName, localityStr})
+	// Set the locality weight to 1. This is required because the child policy
+	// like wrr which relies on locality weights to distribute traffic. These


This is also weighted_target (which has a parent policy of wrr_locality, whose only responsibility is to build the config for weighted_target) and not wrr (which is weighted_round_robin and is a completely different policy).

easwars · 2026-01-22T04:24:27Z

internal/xds/balancer/clusterresolver/resource_resolver_dns.go

-			endpoints[i] = resolver.Endpoint{Addresses: []resolver.Address{a}}
-			endpoints[i].Attributes = a.BalancerAttributes
-		}
+		endpoints = []resolver.Endpoint{{Addresses: state.Addresses}}


@arjan-bal recently made a change #8812 to ensure that the DNS resolver returns endpoints. So, I think we don't need a special case here for len(endpoints) == 0. Please correct me if I'm wrong.

Right, we don't need that special case.

internal/xds/balancer/clusterresolver/configbuilder_test.go

easwars · 2026-01-22T04:28:32Z

internal/xds/balancer/clusterresolver/configbuilder_test.go

+				Cluster:     testClusterName2,
+				ChildPolicy: tt.xdsLBPolicy,
+			}
+			if diff := cmp.Diff(gotConfig, wantConfig); diff != "" {


When using cmp.Diff, it makes more sense to pass the want as the first argument and the got as the second. And in the error string have (-want, +got). When we do this, and see an error string with some lines which have a prefix of -, we can say that those lines were expected but missing in the output. And similarly, when we see some lines with a prefix of +, we can say that those lines were not expected, but were seen in the output. See go/go-style/decisions#types-of-equality

Here and elsewhere where cmp.Diff is used in this PR.

easwars · 2026-01-22T04:30:52Z

internal/xds/balancer/cdsbalancer/e2e_test/dns_impl_test.go

+	server2 := stubserver.StartTestService(t, nil)
+	defer server2.Stop()
+
+	// Register a manual resolver with the "dns" scheme to mock DNS resolution.


Nit: s/mock/override

See:
https://engdoc.corp.google.com/eng/doc/devguide/testing/doubles/choosing.md?cl=head&polyglot=go
https://engdoc.corp.google.com/eng/doc/tott/episodes/296.md?cl=head

resolve conflicts

…ers (grpc#8733) Fixes : grpc#8153 This PR implements the "Changes to Logical DNS Clusters" section of [gRFC A61 (IPv4/IPv6 Dual-stack Backends)](https://github.com/grpc/proposal/blob/master/A61-IPv4-IPv6-dualstack-backends.md#changes-to-logical-dns-clusters). Currently, `LOGICAL_DNS` clusters in the xDS cluster resolver have their Load Balancing policy hard-coded to `pick_first`. This ensures the semantics of connecting to only one address at a time. This PR updates the `xds_cluster_resolver` logic. The `buildClusterImplConfigForDNS` function removes the hard-coded `pick_first` policy restriction for `LOGICAL_DNS` clusters, allowing them to use the configured LB policy. Also, in the DNS update handler, all resolved addresses are now grouped into a single `resolver.Endpoint`. This ensures that regardless of the configured parent LB policy, the child policy sees a single "backend" endpoint containing all addresses. RELEASE NOTES: * xds: `LOGICAL_DNS` clusters now honor the LB policy configured in the cluster resource, rather than defaulting to a hardcoded `pick_first` policy.

Pranjali-2501 added this to the 1.78 Release milestone Dec 1, 2025

Pranjali-2501 added Type: Feature New features or improvements in behavior Area: xDS Includes everything xDS related, including LB policies used with xDS. labels Dec 1, 2025

Pranjali-2501 requested review from arjan-bal and easwars December 1, 2025 15:06

Pranjali-2501 assigned easwars and arjan-bal Dec 1, 2025

easwars reviewed Dec 1, 2025

View reviewed changes

internal/xds/balancer/clusterresolver/resource_resolver_dns.go Outdated Show resolved Hide resolved

internal/xds/balancer/clusterresolver/resource_resolver_dns.go Outdated Show resolved Hide resolved

internal/xds/balancer/clusterresolver/configbuilder.go Outdated Show resolved Hide resolved

easwars assigned Pranjali-2501 and unassigned easwars and arjan-bal Dec 1, 2025

Pranjali-2501 requested a review from easwars December 3, 2025 17:59

Pranjali-2501 assigned easwars and unassigned Pranjali-2501 Dec 3, 2025

easwars reviewed Dec 3, 2025

View reviewed changes

internal/xds/balancer/clusterresolver/configbuilder.go Outdated Show resolved Hide resolved

internal/xds/balancer/clusterresolver/configbuilder.go Outdated Show resolved Hide resolved

internal/xds/balancer/clusterresolver/configbuilder_test.go Outdated Show resolved Hide resolved

easwars assigned Pranjali-2501 and unassigned easwars Dec 3, 2025

eshitachandwani modified the milestones: 1.78 Release, 1.79 Release Dec 11, 2025

Pranjali-2501 requested a review from easwars December 15, 2025 10:23

Pranjali-2501 assigned easwars and unassigned Pranjali-2501 Dec 15, 2025

easwars reviewed Dec 16, 2025

View reviewed changes

easwars assigned Pranjali-2501 and unassigned easwars Dec 16, 2025

Pranjali-2501 force-pushed the a61 branch from 14e5c8f to fa9a279 Compare December 17, 2025 08:14

Pranjali-2501 requested a review from easwars December 17, 2025 09:06

Pranjali-2501 assigned easwars Dec 17, 2025

Pranjali-2501 requested a review from easwars January 7, 2026 09:36

Pranjali-2501 assigned easwars and unassigned Pranjali-2501 Jan 7, 2026

Pranjali-2501 modified the milestones: 1.79 Release, 1.80 Release Jan 21, 2026

easwars reviewed Jan 22, 2026

View reviewed changes

easwars assigned Pranjali-2501 and unassigned easwars Jan 22, 2026

Pranjali-2501 added 11 commits January 28, 2026 12:17

remove hardcoded 'pickfirst' from logical_dns

bcdff79

resolving comments

7183bc4

resolving comments

d434565

resolve conflicts

resolving comments

1aa62ea

resolving comments

1c62f2e

convert test into e2e test

fc30718

add comment

529067c

resolving comments

3b917f4

fix test

1ac89ad

resolving comments

88e547e

resolving comments

83317b1

Pranjali-2501 force-pushed the a61 branch from 99fc16f to 83317b1 Compare January 28, 2026 13:25

Pranjali-2501 requested a review from easwars January 28, 2026 13:34

Pranjali-2501 assigned easwars and unassigned Pranjali-2501 Jan 28, 2026

easwars approved these changes Jan 29, 2026

View reviewed changes

easwars assigned Pranjali-2501 and unassigned easwars Jan 29, 2026

Merge branch 'master' into a61

41ff069

Pranjali-2501 merged commit 55bfbbb into grpc:master Feb 4, 2026
14 checks passed

Conversation

Pranjali-2501 commented Dec 1, 2025 • edited by easwars Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

codecov bot commented Dec 1, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

Uh oh!

Uh oh!

Uh oh!

easwars commented Dec 1, 2025

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

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!

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!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Pranjali-2501 commented Dec 1, 2025 •

edited by easwars

Loading

codecov bot commented Dec 1, 2025 •

edited

Loading