[Feature] Gateway bypass

[alexellis]

Expected Behaviour

This feature would allow an Ingress record to be created that bypasses the gateway, so that an endpoint can be accessed with absolute minimal latency, by removing an additional hop.

Caveats

Today the IngressOperator, FNI definitions are created in the openfaas namespace which causes an Ingress record to be created in the openfaas namespace pointing at the gateway, which is also deployed in that namespace.

For a bypass mode we will have to deploy all resources a second time into the openfaas-fn namespace because Ingress cannot point into a different namespace - i.e. having an Ingress in openfaas which connects to a service in openfaas-fn. It only works in the first example because the gateway acts as a proxy.

See also: kubernetes/kubernetes#17088