Handle HTTP/2 stream errors in tracker client and LB state updator

[shivamgupta1]

Summary

H/2 stream errors were seen in recent incidents and they aren't handled by the Tracker client currently. Handle Http2Exception.StreamException to fix this.

Testing Done

Added UTs

[bohhyang]

DegraderLoadBalancerStrategyV3 doesn't use StateUpdater. It uses DegraderTrackerClientUpdater to update the client state, which uses DegraderControl which then uses DegraderImpl.

Please adjust the logic there (put behind the config as suggested above) and you may add a UT for DegraderImpl to verify the isHigh result, which is critical to increase computed drop rate (hence quarantine).

[shivamgupta1]

Can we just propagate D2ClientConfig everywhere to avoid having to do this each time a change needs to be made to tracker client, state updater, degrader, etc?

[bohhyang]

It will be weird for inner components like DegraderImpl.Config, DegraderTrackerClientImpl, etc. to hold a D2ClientConfig, which is the upper/larger layer that's supposed to control everything in d2 client.

[shivamgupta1]

In that case, can a new config object be created for the LB components such as tracker clients, state updater, etc.? It is essential for new code to be open for extensions.

[bohhyang]

adding a StateUpdater.LoadBalanceConfig makes sense. But adding one to TrackerClientFactory will be hard since the createTrackerClient method is static. We could change that altogether for sure.

[bohhyang]

Added TODOs for optimizing config management later.
Since we don't have bandwidth to address this now, and this PR is for an Incident action item, it doesn't worth holding off the merge for this optimization now.

[bohhyang]

The way the config (in D2ClientConfig) is passed in is:

1. Relative LB: D2ClientBuilder -> RelativeLoadBalancerStrategyFactory -> StateUpdater.
2. Degrader LB:
   1. ZK: ZKFSLoadBalancerWithFacilitiesFactory -> ZKFSTogglingLoadBalancerFactoryImpl -> SimpleLoadBalancerState -> TrackerClientFactory -> DegraderTrackerClientImpl -> DegraderImpl.Config
   2. xDS: XdsLoadBalancerWithFacilitiesFactory -> XdsFsTogglingLoadBalancerFactory -> SimpleLoadBalancerState -> Same as ZK above.

updated

[bohhyang]

aligned that we'll leave the config optimization as a TODO for future. Merging this in as an urgent incident action item.