PodInterface should have Watch method behaving in the same way as ServiceInterface.Watch does.

Use case: a monitoring system (namely Prometheus) expects to get the list of monitored servers performing a DNS-SD query. Special service (similar to kube2sky shipped with Kubernetes) mirrors status of running Pods into etcd, which is in turn monitored by SkyDNS server and exported as DNS-SD. Schematically the data flow looks like this: Kubernetes -> kube2sky -> etcd -> SkyDNS -> Prometheus.

The biggest challenge is to deliver list of all running pods from Kubernetes to kube2sky. Currently kube2sky can only poll Kubernetes with PodInterface.List() each N seconds, which is not efficient. Having a Watch method would be much better.