Support `internalTrafficPolicy: Local` for upstream services without `service-upstream` annotation

[AleksaC]

By default the ingress nginx uses all endpoints of a service in the upstream configuration. This has benefits like allowing proxy_next_upstream to be used, having more even request distribution to upstreams as well as not using conntrack.

However in some cases it is beneficial to avoid traffic between nodes, which can be achived by setting internalTrafficPolicy: Local. In this case it would be useful if ingress nginx only added node-local endpoints to the upstream configuration, avoiding cross-node traffic to the service without having to use service-upstream annotation.

This behavior can be controlled by a flag similar to EnableTopologyAwareRouting that's already supported by ingress nginx.

[k8s-ci-robot]

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[strongjz]

Then why not just use EnableTopologyAwareRouting ?

[AleksaC]

I did that, however in this case I'd prefer if there was no traffic between the nodes, even in the same AZ. Also it seems that EndpointSlice controller falls back to cluster-wide routing if there is a small number of endpoints per zone.