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A61 update: remove special case for LOGICAL_DNS clusters #477

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Mar 6, 2025
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A61 update: remove special case for LOGICAL_DNS clusters #477

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A61 update: remove special case for LOGICAL_DNS clusters
markdroth Mar 1, 2025
495500a
add updated-by to A37
markdroth Mar 1, 2025
bf0ceca
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markdroth Mar 6, 2025
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1 change: 1 addition & 0 deletions A37-xds-aggregate-and-logical-dns-clusters.md
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Expand Up @@ -6,6 +6,7 @@ A37: xDS Aggregate and Logical DNS Clusters
* Implemented in: C-core, Java
* Last updated: 2021-05-06
* Discussion at: https://groups.google.com/g/grpc-io/c/bZ7wLIdNCVY
* Updated by: [A61: IPv4 and IPv6 Dualstack Backend Support](A61-IPv4-IPv6-dualstack-backends.md)

## Abstract

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19 changes: 18 additions & 1 deletion A61-IPv4-IPv6-dualstack-backends.md
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Expand Up @@ -4,7 +4,7 @@ A61: IPv4 and IPv6 Dualstack Backend Support
* Approver: @ejona86, @dfawley
* Status: Ready for Implementation
* Implemented in: C-core
* Last updated: 2025-02-13
* Last updated: 2025-03-06
* Discussion at: https://groups.google.com/g/grpc-io/c/VjORlKP97cE/m/ihqyN32TAQAJ

## Abstract
Expand Down Expand Up @@ -53,6 +53,7 @@ for session affinity behavior in xDS.
* [gRFC A56: Priority LB Policy][A56]
* [gRFC A55: xDS-Based Stateful Session Affinity][A55]
* [gRFC A60: xDS-Based Stateful Session Affinity for Weighted Clusters][A60]
* [gRFC A37: xDS Aggregate and Logical DNS Clusters][A37]
* [gRFC A62: pick_first: Sticky TRANSIENT_FAILURE and address order
randomization][A62]
* [gRFC A50: Outlier Detection Support][A50]
Expand Down Expand Up @@ -791,6 +792,19 @@ def Pick(pick_args):
return result
```

#### Changes to Logical DNS Clusters

Currently, as per [gRFC A37][A37], we handle LOGICAL_DNS clusters by
hard-coding the cluster's LB policy to pick_first, so that we get the
proper semantics of connecting to only one address for the cluster
at a time. However, now that we have the ability to encode multiple
addresses per endpoint, we can do away with that special case. Instead,
the xds_cluster_resolver LB policy will encode all addresses returned by
the DNS resolver as a single endpoint. Regardless of which LB policy
is configured for the cluster, this will result in all addresses being
passed down to the same pick_first child policy, thus providing the
desired behavior without the special case.

### Temporary environment variable protection

The code that reads the new EDS fields will be initially guarded by an
Expand Down Expand Up @@ -904,6 +918,8 @@ Reporting Mechanism](#generic-health-reporting-mechanism).
(https://github.com/grpc/grpc/pull/34526)
- change stateful session affinity to handle multiple addresses per endpoint
(https://github.com/grpc/grpc/pull/34472)
- remove special case for LOGICAL_DNS behavior
(https://github.com/grpc/grpc/pull/38248)

### Java

Expand Down Expand Up @@ -933,6 +949,7 @@ N/A
[envoy-design]: https://docs.google.com/document/d/1AjmTcMWwb7nia4rAgqE-iqIbSbfiXCI4h1vk-FONFdM/edit
[A17]: A17-client-side-health-checking.md
[A27]: A27-xds-global-load-balancing.md
[A37]: A37-xds-aggregate-and-logical-dns-clusters.md
[A42]: A42-xds-ring-hash-lb-policy.md
[A48]: A48-xds-least-request-lb-policy.md
[A50]: A50-xds-outlier-detection.md
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