From a startup junkie, but a non-hacker:<p>Is it possible to build a truly scalable application with all of the Amazon's Web Services? What would be the biggest problem? Is it a technical problem, in that Amazon's services just don't cover everything or is it more that we don't have perfect foresight into where the bottle necks will be?
I've heard this question a lot when people ask me about what Yahoo are going to be offering in the cloud.<p>A lot of people don't understand the difference between Amazon's and Google/Microsoft's approach to cloud offerings.<p>Amazon seem to be providing a lot of infrastructure pieces, from virtulization to storage and CDN to RDMS. However how you connect those pieces or which you use it's pretty much up to you.<p>Google on the other (and Microsoft judging by the current descriptions of Azure) have provided a platform which guides developers towards good practices with constraints but is more limited in the possible applications. That said they won't make your application performs, they'll just make sure it fits in their scalable architecture.<p>So the short answer is yes. You can build a truly scalable application on any or all of these cloud services if you know how. If you know how, though, you can probably do it without them.
There are various levels of Scalabilty, AWS being one of them in a chain.<p>Hosting > AWS > CDN's like Akamai > building out your data center similar to google.<p>AWS is a good start, and if you start doing 100's of Gbps of traffic you should probably start looking for other options.<p>As the other HN commenters have mentioned, you have to architect you application with scalability baked in. Some applications aren't good candidates for scalable applications such as many 1-1 live streams.
Right now, I'd say that the biggest limit to scalability with AWS is the lack of load balancing. They've said that this will be coming in the future; but it's not here yet.