I have been working with Amazon EC2 to run several instances of Windows 2003 Server to test and develop a solution. I am using Windows 2003 Server on Amazon EC2 instead of running several virtual machines locally because:

• I want a usable system - my computers have 4Gb max RAM, so I can run two instances per computer but things get really slow
• I need to understand networking issues - local VMs are all on the same network, so it's easy to get things running (this is usually good, but I need something that's more realistic)
• I am testing scalability - Amazon EC2 can start new instances as necessary (and stop them too), based on overall load - I can't simulate that with local VMs
• I don't need durable VMs - my VMs are generic enough so that I can just start one and use it - not much configuration is necessary. It really does not justify the 40Gb of space I need for each instance

So far, I have been configuring instances to refer to each other by name (the NetBios name) by editing the hosts file. I wanted something more robust, so WINS is the most logical choice (combined with DHCP).

After much experimenting with the default, small, non-authenticated instance, I was unable to get WINS or DHCP running. While you can use DHCP and WINS on EC2, you need to use an instance of Windows with Authentication Services.

While Windows with Authentication Services implies that authentication refers only to users, it actually refers to all inter-instance communications that require authentication at the system level. 

So, why this post? It might save you a few hours of testing time since the EC2 documentation is not clear about this point.