It costs engineering time to simply choose Amazon in the first place. You could spin up VPSes at backspace or dedicated machines elsewhere for less money, and have a local, reliable, fast hard drive.
Instead, to go with amazon you have to architect for Amazon, not counting on your ECC instances to be up all the time, accounting for their local fast storage going away, or accounting for how EBS, which is persistent, is slow.
The alternative is, get the enterprise version of Riak, purchase dedicated nodes in two data centers, tell them about each other. (no engineering required.)
If engineering resources are the most precious commodity, it seems AWS is the more expensive option.
Instead, to go with amazon you have to architect for Amazon, not counting on your ECC instances to be up all the time, accounting for their local fast storage going away, or accounting for how EBS, which is persistent, is slow.
The alternative is, get the enterprise version of Riak, purchase dedicated nodes in two data centers, tell them about each other. (no engineering required.)
If engineering resources are the most precious commodity, it seems AWS is the more expensive option.