[EKS] [request]: AWS LB Controller integration with Flagger

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**Tell us about your request**
We would like an integration between Flagger and the standard EKS ingress controller, the AWS Load Balancer Controller.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We currently use the AWS Load Balancer Controller. We would like to run canary deployments and use rolling updates when applying changes to the primary/stable service. As it stands, in order to use the most popular release controller, Flagger, we would have to switch ingress controllers.

**Are you currently working around this issue?**
We're currently using Argo Rollouts, but it's missing support for several service meshes, including App Mesh, which we would like to try when we move enough services to Kubernetes to call for a service mesh. We are not keen on running different release controllers based on whether a service handles Ingressed traffic. Flagger also has several features that Argo Rollouts does not, such as built-in management of configmaps/secrets, separate HPAs for the primary and canary services, and rolling updates when applying changes to the stable/primary service. We have implemented subpar workarounds for all three of these features, among others.

**Additional context**
There's an open Issue in Flagger for the integration: https://github.com/fluxcd/flagger/issues/659. Questions around integration tests and maintenance costs remain unanswered. I believe both AWS and your users would benefit from AWS support for an integration to your platform on the most popular Kubernetes release controller.

Start by reviewing the linked Flagger issue 659 and the AWS Load Balancer Controller and EKS integration requirements described here. Define the integration scope, testing approach, and maintenance expectations; done means Flagger can support canary deployments and stable-service rolling updates with the standard EKS ingress controller.

Written by the indexing model from the issue text.