Moving 100k customers from co-lo data centres to the cloud. With zero downtime

How much it used to cost vs how much it costs now is one of those questions that always gets asked (of course!) but it's almost impossible to answer to anyone's satisfaction. There's more to value and benefits than just the numbers on the bill.

My stock answer here (for us) is that it is more expensive to run in AWS, but not by a significant amount, and the flexibility being in the cloud provides is orders of magnitude more valuable than this outlay when all the many other factors are taken into account. Building active-active infra and coping with an anticipation of doubling or tripling customer numbers is a major headache and cost in our DC world. In the cloud it's a minor concern.

I can tell you that the monthly AWS bill is somewhere around £90,000 right now, unoptimised. The co-lo DC cabinets/power/bandwidth bill used to be around £15,000 a month, without taking into account any of the capitalised costs of the initial hardware outlay (a lot), depreciation, replacements, service/maintenance contracts, staff costs and so on.

HTH.