An Architect's vision

1. AMI is region specific. It means that if I create an AMI in us-east-1, I will not be able to use that AMI in any another region.  2. Workaround of the above issue is to copy the ami to other region.  3. Two virtualization type, HVM and Paravirtualizatio 4. Windows only use HVM 5. Linux / Unix can be on both 6. If we create AMI while the instance is running. Instances will be unavailable for the moment till the snapshot of EBS volume will get created. As soon as snapshot of EBS volume gets created, we 2/2 checks happen and you will be able to see the Instance online  7. If you create AMI during runtime of EC2 instance, there are chances that your filesystem will get corrupted. In that case if you don't have proper backup, you can not restore it back.  8. Idle case create AMI while instance is shutdown.  9. Need to take care of reboot option. 

In this model even with a single site to site VPN tunnel we can handle multiple VPC.  Note:  1. Rare case reference available in this case.  2. Might have performance issues.  3. Only one Public IP is sufficient. 

In this model we need separate site to site VPN tunnel for separate VPCs in a single region.  Note: More VPN pairing would be required if we want communication between VPCs.  Management would be tricky.  Need more Public IPs in this case. 

Amazon supports following two virtualization types 1. HVM (Hardware assisted Virtual Machine) It provides complete hardware isolation. 2. Paravirtualization Note: Windows EC2 runs on only on HVM. Linux / Unix can run on both HVM / Paravirtualization