If you allocate an Elastic IP address in the US-East region (N.Virginia), then sorry folks but you can’t use this IP address with an EC2 instance which is located in another region, say EU-West (Ireland) for example.
No problem to remap it to an EC2 instance in another availability zone within the same region.

The documentation of Amazon EC2 leaves another impression:

Elastic IP addresses allow you to mask instance or Availability Zone failures by programmatically remapping your public IP addresses to any instance in your account.

This is a bit misleading. I already had started dreaming as how I can transfer my EC2 instance across continents with no DNS propagation issues. And also had started admiring Amazon as to how they achieved this technically… Well, they haven’t. 🙂

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References:

• My inquiry about this in the AWS->EC2 forum.