Yeah but that's what capex based stuff (like buying and colocating) is: planning for scale. With AWS you think you need a robust DB and shit and you've made a decision that can be undone in minutes.
You think you want Elasticache? It's a fifteen minute operation. In that time your devops guy isn't going to have even downloaded the binary and figured out the docs.
As I wrote further up, there's not just colocation and AWS. Dedicated servers are a great fit for many start ups and need no capex. You just rent hardware monthly like you lease most of your office equipment. Much cheaper than AWS, no hardware expertise needed and even (manual) scaling over time works quite well, it's easy to add servers within a day or so.
Sure, you'll always have idle capacity, but this way you could use it. With AWS, Amazon runs that idle capacity and charges you for it.
> With AWS you think you need a robust DB and shit and you've made a decision that can be undone in minutes.
If it can be undone in minutes, it isn't much of a decision. A service that can be enabled or canceled on a whim is unnecessary.
Realistically, analyzing the guarantees offered by a cloud platform, your corresponding requirements, and how everything is supposed to work is going to take days, and actually developing and testing disaster recovery procedures is going to take even longer.
You think you want Elasticache? It's a fifteen minute operation. In that time your devops guy isn't going to have even downloaded the binary and figured out the docs.