How do people use Iaas (e.g. EC2 at Amazon) & tools to let you do this

....while you can use it in any way you want ----here is some common ideas:

For Web applicaitons

1. Run your base system in minimum # of VMs

2. Monitor the load

3. Load should be distributed to VMs

4. If > threshold then Increase the number of VMs.

5. If load < some threshold Then Decrease number of VMS.

Elastic Block Store = mountable storage, local to each VM instance

Elastic IP address: programmatically remap public IP to any instance

CloudWatch: monitoring EC2 resouces

Auto Scaling: conditional scaling

Elastic load balancing: automatically distribute incoming traffic across instances