Merge pull request kubernetes#499 from diwu1989/patch-1

Update aws_under_the_hood.md to clarify pod vs node instance

Author: philips

aws_under_the_hood.md

@@ -89,8 +89,8 @@ We do not currently run the master in an AutoScalingGroup, but we should
 
 Kubernetes uses an IP-per-pod model. This means that a node, which runs many
 pods, must have many IPs. AWS uses virtual private clouds (VPCs) and advanced
-routing support so each pod is assigned a /24 CIDR. The assigned CIDR is then
-configured to route to an instance in the VPC routing table.
+routing support so each EC2 instance is assigned a /24 CIDR in the VPC routing
+table.
 
 It is also possible to use overlay networking on AWS, but that is not the
 default configuration of the kube-up script.