Have you checked system logs/dmesg? I'd suspect it's an instance problem
too, maybe you'll see some relevant errors in those logs.
We've seen an unusually high instance failure rate with i3's (underlying
hardware degradation). Especially with the nodes that have been around
longer (recently provisioned nodes have a more typical failure rate). I
wonder if your underlying hardware is degraded and EC2 just hasn't noticed
yet.
Just to rule out a simple problem, are you using a load balancing policy?
