[fragsworth]

It takes development/engineering resources, and additional hardware resources to make your architecture more fault-tolerant and to maintain this fault-tolerance over long periods of time.

Weigh this against the estimated costs of your application going down occasionally. It's really only economical for the largest applications (Netflix, etc.) to build these systems.

[gazarsgo]

disagree. the only area it really hurts the wallet is multi-AZ on your RDS, because it doubles your cost no matter what and RDS is toughest to scale horizontally. The upside is if you scale your data layer horizontally you don't need to use RDS anymore.

two c1.medium, which are very nice for webservers, are enough to host >1M pageviews a month (wordpress, not much caching) and cost around $120/mo each, effective $97/mo if you prepay for 12months at a time via reserved instances.

[piggity]

The other issue is that you can have redundant services, but when the control plane goes down - you are screwed.

Every day I have to build basic redundancy into my applications I wish that we could just go with a service provider (like Rackspace / Contegix) that offered more redundancy at the hardware level.

I know the cloud is awesome and all, but having to assume your disks will disappear, fail, go slow at random uncontrollable times is expensive to design around.

If you don't have an elastic load, then the cloud elasticity is pointless - and is ultimately an anchor around your infrastructure.