Merge pull request #4455 from ElvinEfendi/zone-aware-routing-kep

KEP: availability zone aware routing

docs/enhancements/20190815-zone-aware-routing.md

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+---
+title: Availability zone aware routing
+authors:
+  - "@ElvinEfendi"
+reviewers:
+  - "@aledbf"
+approvers:
+  - "@aledbf"
+editor: TBD
+creation-date: 2019-08-15
+last-updated: 2019-08-15
+status: provisional
+---
+
+# Availability zone aware routing
+
+## Table of Contents
+
+<!-- toc -->
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+<!-- /toc -->
+
+## Summary
+
+Teach ingress-nginx about availability zones where endpoints are running in. This way ingress-nginx pod will do its best to proxy to zone-local endpoint.
+
+## Motivation
+
+When users run their services across multiple availability zones they usually pay for egress traffic between zones. Providers such as GCP, AWS charges money for that.
+ingress-nginx when picking an endpoint to route request to does not consider whether the endpoint is in different zone or the same one. That means it's at least equally likely
+that it will pick an endpoint from another zone and proxy the request to it. In this situation response from the endpoint to ingress-nginx pod is considered as
+inter zone traffic and costs money.
+
+
+At the time of this writing GCP charges $0.01 per GB of inter zone egress traffic according to https://cloud.google.com/compute/network-pricing.
+According to https://datapath.io/resources/blog/what-are-aws-data-transfer-costs-and-how-to-minimize-them/ AWS also charges the same amount of money sa GCP for cross zone, egress traffic.
+
+This can be a lot of money depending on once's traffic. By teaching ingress-nginx about zones we can eliminate or at least decrease this cost.
+
+Arguably inter-zone network latency should also be better than cross zone.
+
+### Goals
+
+* Given a regional cluster running ingress-nginx, ingress-nginx should do best effort to pick zone-local endpoint when proxying
+
+### Non-Goals
+
+* -