[bigiain]

Except when either your app server or db server go down on a Friday night (sods law implies this will happen on a weekend you're heading out of town).

Now your 100k/month platform is down for 3 days.

You've saved something like $40/month (two additional app/db vms plus a load balancer), but a failure could realistically cost you 1/10th of a month of downtime (which, simplistically looks like $10k). Do you think your platform with two single points of failure is _not_ going to go down like this sometime in the next 5 years?

(Of course, a weekend's worth of downtime might not be a 10% revenue hit - but depending on your SLAs and penalties it's also possible to be a lot more than that...)