Expand allowed types to accommodate custom service discoverer events #2379
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idelpivnitskiy
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Motivation: Clients have a configurable `serviceDiscovererRetryStrategy` to guarantee a steady stream of events to the `LoadBalancer` that never fails. It's necessary at the client level to avoid hanging requests indefinitely and let requests observe failures from ServiceDiscoverer. Also, for `PartitionedHttpClient` it's necessary to guarantee that `GroupedPublisher` never fails. Retry is effectively a re-subscribe. According to `ServiceDiscoverer` contract (clarified in apple#3002), each `Subscriber` receives a "state of the world" as the first collection of events. The problem is that the state may change significantly between retries, as a result unavailable addresses can remain inside the `LoadBalancer` forever. Example: T1. SD delivers [a,b] T1. LB receives [a,b] T1. SD delivers error T2. SD info changed ("a" got revoked) T3. Client retries SD T3. SD delivers [b] T3. LB receives [b] (but still holds "a") When we retry `ServiceDiscoverer` errors, we should keep pushing deltas downstream or purge events that are not present in the new "state of the world". We previously had this protection but it was mistakenly removed in apple#1949 as part of a broader refactoring around `ServiceDiscoverer` <-> `LoadBalancer` contract. Modifications: - Add `RetryingServiceDiscoverer` that handles retries and keeps the state between retries. - Use it in `DefaultSingleAddressHttpClientBuilder` and `DefaultPartitionedHttpClientBuilder`. - Use `CastedServiceDiscoverer` to allow modifications for `ServiceDiscovererEvent` after we started to use a wildcard type in apple#2379. - Pass consistent `targetResource` identifier to both `RetryingServiceDiscoverer` and `LoadBalancerFactory` to allow state correlation when inspecting heap dump. Result: Client keeps pushing deltas to `LoadBalancer` after retrying `ServiceDiscoverer` errors, keeping its state consistent with `ServiceDiscoverer`.
idelpivnitskiy
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…3006) Motivation: Clients have a configurable `serviceDiscovererRetryStrategy` to guarantee a steady stream of events to the `LoadBalancer` that never fails. It's necessary at the client level to avoid hanging requests indefinitely and let requests observe failures from ServiceDiscoverer. Also, for `PartitionedHttpClient` it's necessary to guarantee that `GroupedPublisher` never fails. Retry is effectively a re-subscribe. According to `ServiceDiscoverer` contract (clarified in #3002), each `Subscriber` receives a "state of the world" as the first collection of events. The problem is that the state may change significantly between retries. As a result, unavailable addresses can remain inside the `LoadBalancer` forever. Example: T1. SD delivers [a,b] T1. LB receives [a,b] T1. SD delivers error T2. SD info changed ("a" got revoked) T3. Client retries SD T3. SD delivers [b] T3. LB receives [b] (but still holds "a") When we retry `ServiceDiscoverer` errors, we should keep pushing deltas downstream or purge events that are not present in the new "state of the world". We previously had this protection but it was mistakenly removed in #1949 as part of a broader refactoring around `ServiceDiscoverer` <-> `LoadBalancer` contract. Modifications: - Add `RetryingServiceDiscoverer` that handles retries and keeps the state between retries. - Use it in `DefaultSingleAddressHttpClientBuilder` and `DefaultPartitionedHttpClientBuilder`. - Use `CastedServiceDiscoverer` to allow modifications for `ServiceDiscovererEvent` after we started to use a wildcard type in #2379. - Pass consistent `targetResource` identifier to both `RetryingServiceDiscoverer` and `LoadBalancerFactory` to allow state correlation when inspecting heap dump. Result: Client keeps pushing deltas to `LoadBalancer` after retrying `ServiceDiscoverer` errors, keeping its state consistent with `ServiceDiscoverer`.
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Motivation:
The types in the client builders are too restrictive and prevent us from using
them with custom ServiceDiscoverers with custom ServiceDiscovererEvent
implementations.
Changes:
Open up the types so we can use these APIs with a larger selection of custom
ServiceDiscoverers. This change is not breaking.