EC2 Instances will not keep elastic IP

Question

So, I don't understand what is going on here... I have (3) Micro EC2 Instances which are launched (without elastic ip)

I then go to Network Security->Elastic IPs and click associate IP address. I chose a running EC2 instance, that instance then uses the elastic ip.

If I stop, then start this SAME ec2 instance, it doesnt have the same previous elastic IP address and is instead some completely new IP address. This is messing up scripts that then depend on the previously associated elastic ip to that EC2 instance.

Why is this happening and why cant i get any of the (3) instances to adopt and keep this assigned elastic ip?

Answer 1

If you create a VPC and then re-provision the 3 micro instances under the VPC, EIPs you associate will remain associated during stop/start cycles. You won't be able to reuse your existing EC2 instances or EIPs; you'll have to recreate them under the new VPC.