LoadBalancer should always consider the first events as initial state #3004
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Motivation: Currently, both implementations of the `LoadBalancer` assume 2 possibilities for the first events collection after re-subscribe: "state of the world" or "delta" and tries to infer which one it is based on what event statuses are present in the collection. However, it doesn't provide any guarantees because even if SD impl keeps returning deltas after a re-subscribe, a delta can contain only `AVAILABLE` events, but it will be incorrectly interpreted as "state of the world". Because of Reactive Streams rule clarified in apple#3002, `LoadBalancer` implementations should always expect "state of the world" for the first events after re-subscribe. Modifications: - Remove inference of the first collection of events after resubscribe and always expect a new subscriber to start from "state of the world". - Update `resubscribeToEventsWhenAllHostsAreUnhealthy()` test to reflect behavior change. Result: Both `LoadBalancer` implementations follow `ServiceDiscoverer` contract and expect the first collection of events after re-subscribe to represent a "state of the world".
bryce-anderson
approved these changes
Jul 12, 2024
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Motivation:
Currently, both implementations of the
LoadBalancerassume 2 possibilities for the first events collection after re-subscribe: "state of the world" or "delta" and try to infer which one it is based on what event statuses are present in the collection. However, it doesn't provide any guarantees because even if SD impl keeps returning deltas after a re-subscribe, a delta can contain onlyAVAILABLEevents, but it will be incorrectly interpreted as "state of the world".Because of Reactive Streams rule clarified in #3002,
LoadBalancerimplementations should always expect "state of the world" for the first events after re-subscribe.Modifications:
resubscribeToEventsWhenAllHostsAreUnhealthy()test to reflect behavior change.Result:
Both
LoadBalancerimplementations followServiceDiscoverercontract and expect the first collection of events after re-subscribe to represent a "state of the world".