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I'm running SQL Server in Amazon EC2. I was taking a look at netstat (netstat -f) to sample the active connections on my local database. Everything looks as I would hope, except for an unexpected entry that appears related to EC2:

(All numbers below are modified so as to protect my actual server info).

Proto Local Address      Foreign Address                                   State
TCP   domU-12-34-56-78-90-12.compute-3.internal:56789   ESTABLISHED
... would be my local database address and port in this case.

Anything.compute-x.internal clearly looks EC2-related. Note that I do not have any CloudWatch alarms or load balancing associated with this server. So the question is-- what is this domU connection and why is it connected to my database?

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up vote 4 down vote accepted

DomU is a Xen term - it's a virtual machine. The name you see really has nothing to do with that, though. netstat does a reverse IP lookup on the remote end of the connection; this name is what the remote IP resolved to. Add a -n flag to netstat to see the actual IP address that connected.

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Ah, seems some internal host names are prefixed with ip- while others are domU-. The ip- named were clearly my other instances, but the domU- at first glance didn't appear to be such. The IP address matched up though. Mystery solved. Thanks. – DuckMaestro Feb 29 '12 at 7:39

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