XMPP Server on EC2 Amazon Web Service (AWS)

Solution 1:

AWS will work for what you intend without any problem, things to be aware though of an EC2 implementation

• You'll lose CPU cycles when the underlying node is under high load, be ready for your machines to sometimes not deliver enough CPU juice
• Disk I/O will be a bit slower than a regular machine

Apart from that Openfire does have a clustering solution, which is commercial, and as far as I know the company behind it died (and they haven't open sourced it, gah), I've been trying to contact them to get the clustering solution myself, to no avail.

So if you choose Openfire you'll be stuck with one server having to carry all the workload, which sounds a bit stressing with the numbers you're talking about, if you want to start with Openfire it looks like a good easy way to get rolling but when you need to be aware of your options when you start to grow ;)

For tutorials have a look at the Openfire howto at http://ubuntuforums.org/showthread.php?t=525670, it's not a bad one :)