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When I spin up a machine in us-west-2 and give it an elastic IP, it gets a public DNS hostname like

When I spin up a machine in us-east-1 and give it an elastic IP, it gets a public DNS hostname like

Why the difference?

When I reassociate an elastic IP, will the public DNS hostname be the same?

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Since you got the elastic IP you should use it and not CNAME to this DNS record. – Andrew Smith Jun 30 '12 at 9:45
up vote 2 down vote accepted

Well if you wonder for such a details, the difference is because European datacentre was established after the US one, so the Europe got the sub-domain, while the US kept the original short version to preserve the backwards compatibility and increase stability of already deployed services.

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Thanks! Sounds plausible enough. Accepted. – Adam Monsen Jul 22 '12 at 4:35

Elastic ips' public DNS hostname always stays the same. When you associate an elastic ip to instance, the instance's public DNS hostname changes.

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