I have read on session affinity for ingress and istio, which is based on envoy
I understand session affinity can make the same header go to the same pod. but say a single header is doing a large amount of requests and a single pod cannot handle it, is it possible to have multiple pods/or a service affiliate with this header and load balance the requests.
Is there any way to have session affinity on a group of pods, doesn't have to be ingress or istio
You should look for a custom solution by using the NGINX Ingress controller and refer to this for Ingress classes. If you are getting a large number of requests then you should look into pods limitations.