"A replication controller ensures that a specified number of pod "replicas" are running at any one time. " As it is said, who will decide the "specified number of pods" for replication controller? It seems like that we can set the number. And is there any auto-scaler who will did this thing?
The person who creates (or updates) the replication controller decides.
There is no autoscaler yet, but it is something the community will be looking at post-1.0.
edit: Autoscaling is now available for the number of pods in replication controllers: http://kubernetes.io/docs/user-guide/horizontal-pod-autoscaler/