With so many database options available these days, like for the rest of life, it's natural to wonder how it all fits together. Amazon complicated, or rather expanded the available options by introducing RDS, their relational database service. RDS is MySQL safely cocooned as a manageable cloud element, resting boldly within an energy providing elastic CPU pool, supported by a virtually infinite supply of very capable virtualized storage .
MySQL in AWS is now easy to start, stop, monitor, backup, snapshot, expand, and effortlessly move up and down the instance hierarchy. What it's not, contrary to what you might expect, is a scale-out solution, it's a scale-up solution. You get more by buying a bigger instance, not by horizontally adding more instances. There's a limit. Admittedly a larger limit now with Amazon's new high memory instances.
That's OK, well maybe not for people who helped grow Amazon's ecosystem by offering a similar product, but so many projects use MySQL that this is a big win for a lot of people. It makes life easier even if the promise of infinite relational database storage is yet to be realized.
If one of the reasons you were considering using a Platform as a Service is to knock the database item off your worry list, RDS is one more reason to consider playing your own general contractor and orchestrating all the elements together yourself. As more services become packaged into cloud capable components this is likely how many systems will be bolted together in the future.
But we are left wondering, how RDS fits together with SimpleDB and all the other database options?