[heax]

If you want the cloud to be a powerful tool you will use their higher level services. These are incompatible and cannot be reasonably abstracted away.

The simple services like files which you could reasonably abstract away in your code you can also migrate when needed.

If you don't want lock in you might be better of with a traditional hosting provider. The cloud is only really useful if you go in with a mindset to embrace what it offers.