<t>"Cloud" is such a vague term. Still, I think this is a very good question.<br/>
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Basically, IaaS cloud hosting does not magically make your application scale. It's really a virtual private server with very short contract / cancellation periods.<br/>
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For scalability, the magic lies not so much in the hosting, but in the horizontal scalability of the application code itself. This is related to all the distributed computing challenges. For example, adding more application servers is not always easy: you must be sure that you don't persist any user state in the server application (but rather in a database, static can be evil), caching can be problematic because local caches can make the situation worse if you're using a round-robin strategy, etc.<br/>
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- What is your experience with application transition to cloud and which one did you choose and why?<br/>
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- What would you recommend I should think about when designing/developing the solution to make the transition as painless as possible.<br/>
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You don't really have to do anything different just to host on EC2 or Azure -- basically. But of course, it's not that easy when things grow.<br/>
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For instance, EC2 instance storage is rather limited. Additional storage on EBS, however, does not provide comparable performance characteristics and can be a bit more laggy than a disk. The point here is that EBS does magically scale, and it's probably more PaaS than IaaS; but it's not a simple hard disk and it does, consequently, not behave like a hard drive. I don't know about Azure block storage. In general, expect additional abstraction layers to introduce problems of their own, no matter what they do.<br/>
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- Based on your experience is it better to move to the cloud (financial wise) or is it better to buy your own servers and load balance application yourself and maybe save money on the long run?<br/>
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Typical cloud providers are more expensive than the usual 'round-the-corner VPS providers, but they are, to my experience, also much more reliable and professional. EC2 has a free tier (but it's quite small), Azure gives you a small instance for free for 3 months.<br/>
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Doing the calculation right is rather tricky; for example, if you have to shut down your service for whatever reason, it's nice to be able to cancel now rather than pay another year - you might want to put this risk into your calculation. On the other hand, both EC2 and Azure will be considerably cheaper if you sign up for 6 or 12 months, rather than paying by the hour.<br/>
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You might want to check out the free Azure plan, because it's nice to start fiddling around without any cost. A big advantage of cloud providers is that you can scale vertically very easily: buying a 16 core, 64GB RAM server machine is really expensive, but if there's so much traffic on your site, upgrading your plan won't be such a big issue.</t>
