feat(tonic-xds): implement gRFC A50 outlier detection success-rate algorithm#2673
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LYZJU2019 wants to merge 1 commit into
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feat(tonic-xds): implement gRFC A50 outlier detection success-rate algorithm#2673LYZJU2019 wants to merge 1 commit into
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…gorithm grpc#2619 landed the failure-percentage algorithm and the shared sweep plumbing. This change fills in the second A50 ejection algorithm: success-rate (cross-host mean/stdev). Algorithm (run before failure-percentage in the same sweep, gated by SuccessRateConfig being present on the cluster config): 1. For each host with total >= request_volume, compute its success rate as a percentage in 0.0..=100.0. 2. If fewer than minimum_hosts qualify, skip the algorithm. 3. Compute mean and population stdev of the success rates. 4. threshold = mean - stdev * stdev_factor / 1000 5. For each qualifying host whose success rate is strictly below the threshold, attempt ejection — subject to max_ejection_percent (with A50's at-least-one floor) and the enforcing_success_rate roll. Hosts already ejected (e.g., by a previous algorithm in this sweep) are skipped, and ejections feed into ejected_count so the subsequent failure-percentage pass respects the cap. Success-rate runs first because A50 lists it first and Envoy's implementation runs the algorithms in the same order; the two algorithms are otherwise independent. Seven new unit tests cover the outlier-below-threshold happy path, uniform-population no-eject (stdev = 0), minimum_hosts gating, request_volume filtering, enforcement = 0 no-op, stdev_factor = 0 collapsing to the mean, max_ejection_percent interaction, and combined success-rate + failure-percentage composition.
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Motivation
#2619 landed the failure-percentage algorithm and the shared sweep plumbing. This PR fills in the second gRFC A50 ejection algorithm: success-rate (cross-host mean/stdev).
Solution
In the housekeeping sweep, the success-rate algorithm now runs before the failure-percentage algorithm (A50 lists them in that order, and Envoy's implementation follows the same order; the two algorithms are otherwise independent and gated separately).
Tests
Seven new unit tests covering:
success_rate_ejects_outlier_below_threshold— 4× 100% + 1× 0%, mean=80, stdev=40, threshold@1900 = 4 → outlier ejected.success_rate_uniform_population_does_not_eject— stdev=0 → threshold=mean, nothing strictly below.success_rate_minimum_hosts_gates_ejection— qualifying<minimum_hosts → algorithm skipped.success_rate_request_volume_filters_low_traffic— low-volume outlier excluded from population and candidates.success_rate_enforcement_zero_never_ejects—enforcing_success_rate = 0short-circuits the roll.success_rate_stdev_factor_zero_ejects_below_mean— factor=0 collapses threshold to the mean.success_rate_max_ejection_percent_caps_concurrent_ejections— cap (with floor) holds.success_rate_and_failure_percentage_compose— both algorithms configured: success-rate ejects, failure-percentage skips already-ejected host (no double-count).All 33 tests in
client::loadbalance::outlier_detectionpass, including the 26 from #2619.