tonic-xds: Add A32 circuit breaking limiter by mingley · Pull Request #2711 · grpc/grpc-rust

mingley · 2026-06-30T16:59:12Z

Summary

gRFC A32 circuit-breaking configuration is parsed by tonic-xds, but request enforcement is not yet in the channel path. This PR adds the reusable limiter primitive first so its request-lifetime and state-management behavior can be reviewed independently before production CDS/channel wiring lands. It is part of #2444.

Enforce max_requests with process-global in-flight counters keyed by cluster and EDS service name, while retaining per-channel drop accounting for future LRS integration (36b03763, 4a20f392, c6b89daa).
Admit calls only after the wrapped per-cluster service is ready, so queued work does not consume capacity, and mark local UNAVAILABLE drops so gRPC retry policy does not retry them (c6b89daa).
Hold permits through the full response-body lifetime and release them on trailers, body errors, completion, response-future cancellation, or response drop (36b03763, c6b89daa).
Apply live limit changes without resetting in-flight counts and clean up counters across EDS service-name changes, config removal/recreation, and channel teardown (c4559d3e, 4a20f392, c6b89daa).
Cover the default 1024-request boundary, process-wide sharing, per-channel drop attribution, retry behavior, readiness, cancellation, and counter cleanup (c6b89daa).

Testing Done

cargo fmt --all --check
cargo clippy -p tonic-xds --lib --all-features -- -D warnings - passed
cargo test -p tonic-xds circuit_breaking --lib - 23 passed, 0 failed
cargo test -p tonic-xds --all-features - 389 unit tests and 4 doc tests passed
gh pr checks 2711 --repo grpc/grpc-rust - all non-skipped PR checks passed

linux-foundation-easycla · 2026-06-30T16:59:20Z

The committers listed above are authorized under a signed CLA.

✅ login: mingley / name: Michael Ingley (4609832)

YutaoMa · 2026-06-30T18:17:37Z

For PRs to tonic-xds, mention that in the PR title for better searchability.

mingley · 2026-06-30T21:40:04Z

For PRs to tonic-xds, mention that in the PR title for better searchability.

updated PR description to track #2444 and also updated title to include tonic-xds

YutaoMa · 2026-07-29T20:51:37Z

The state tracking and retry ignore logic all lgtm. Only comment left is https://github.com/grpc/grpc-rust/pull/2711/changes#r3677940804 where the change needed is to have the empty config fallback (along with the default cluster name helper fns) removed. Lmk once you address those.

mingley · 2026-07-29T21:56:22Z

The state tracking and retry ignore logic all lgtm. Only comment left is https://github.com/grpc/grpc-rust/pull/2711/changes#r3677940804 where the change needed is to have the empty config fallback (along with the default cluster name helper fns) removed. Lmk once you address those.

#2711 (comment)

Brings in the A32 circuit breaking limiter landed in grpc#2711 and reconciles this branch with the retry classifier refactor and cluster discovery connector factory that landed on master. Conflict resolutions: - circuit_breaking.rs: keep this branch's CDS-driven enforcement, which waits for CDS and falls back to the gRFC A32 default of 1024 max_requests. This supersedes the no-config bypass from 79ab667. - retry.rs: take master's RetryClassifier refactor, which already carries the is_local_circuit_breaker_drop check this branch added. - channel.rs: take master's GrpcMakeConnector factory and pre_route interceptor, with circuit breaking layered between routing and retry. - Port tests to master's retry API (RetryConfig/GrpcRetryClassifier) and add the MIT license header to circuit_breaking.rs.

mingley mentioned this pull request Jun 30, 2026

Wire A32 circuit breaking into xDS channels #2712

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mingley force-pushed the mingley/a32-circuit-breaking-core branch 2 times, most recently from 4609832 to 36b0376 Compare June 30, 2026 17:20

YutaoMa reviewed Jun 30, 2026

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