Explain Kubernetes autoscaling and traffic routing

Within Kubernetes:

1. How do autoscaling mechanisms operate, for both pod-level and node-level scaling?
2. How does incoming traffic from outside the cluster get directed to the correct Pods?
3. What separates a ReplicaSet from a StatefulSet, and in which situations would you choose each? Overview: The question tests familiarity with Kubernetes autoscaling, routing of external traffic to Pods, and the distinctions between ReplicaSet and StatefulSet controllers.