Add support for Load Balancing Policy

[arkodg]

What would you like to be added:
The ability for the user to specify the load balancing policy/algorithms used when load balancing requests from the gateway to the upstream / backend.

Why this is needed:
To improve performance/throughput in production.

Examples in Data Plane

• Envoy - https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/upstream/load_balancing/load_balancers
• NGINX - https://nginx.org/en/docs/http/load_balancing.html

Examples in Control Plane

• Contour - https://projectcontour.io/docs/v1.10.0/config/request-routing/#load-balancing-strategy
• Istio - https://istio.io/latest/docs/reference/config/networking/destination-rule/#LoadBalancerSettings

[shaneutt]

For posterity, this has been brought up a few times. Here's some of the prior art:

#1074 #992 #912

Historically we have landed on policy attachment being the suggested method to handle this, however I'm personally OK with seeing where this goes. @youngnick and @robscott should weigh in.

[arkodg]

thanks @shaneutt for surfacing all the prior issues ! would ideally like to see this as a native noun rather than a policy attachment

[shaneutt]

I'm with you that this would be good. To make it happen we're going to need someone who's dedicated to championing it, teasing out all the issues and pushing it forward as a GEP. I think getting this right across multiple implementations is going to be a little tricky.

[arkodg]

thanks, I see how this feature can be related to the Backend Properties proposal outlined in https://github.com/kubernetes-sigs/gateway-api/pull/1333/files .

From an API perspective, the HTTPBackendRef https://gateway-api.sigs.k8s.io/references/spec/#gateway.networking.k8s.io%2fv1beta1.HTTPBackendRef could be a good place to introduce the notion of a backend filter/property to support a load balancing policy.