So I've been spending a lot of time in the financial services/payment space and might be able to answer some of your questions.

The EU activated the Digital Online Resiliency Act (DORA) last year (passed in 2023) which, amongst other things, mandates that financial services providers who run their core business functions in the cloud (i.e. Monzo) must be able to demonstrate that they are not entirely reliant on a single cloud provider. Otherwise, big, big fines.

Like GDPR, there are auditors that are responsible for signing off on EU DORA compliance. Also like GDPR, there are ways to check those boxes without _really_ checking them. This is probably why Stand-In only has 18 services in its GCP failover "region" instead of the 1K+ production services in AWS; it's just enough to keep critical services (payments/card networks, balances, ledger, etc.) operational and, more importantly, keep DORA auditors at bay.

This article IMO is more for other FSIs who _want_ to run _entirely_ in the cloud (there are very, very few that do). Financial services is a very risk-averse industry. Most providers have biz-critical systems running on mainframes still. (Mainframes are practically indestructible and are much more technically-interesting than people give them credit for, but that's another post.) Being able to tell AWS "yeahhhhh we can run this business on GCP and/or Azure in literally 10 minutes" is a money line for procurement to use during price negotiations. Or at least it was until RAM prices mooned hard enough to make their existing datacenter inventory suddenly very attractive.

Cloud-aside, pretty much every bank in the US has some architecture like this for their critical banking systems, except they are usually an old-school hot-cold (sometimes hot-hot) datacenter failover strategy. Historically failover has been done manually with a runbook (with some automation) and tested during DR/BCP days (sometimes more frequently). They, of course, have zonal/regional replication in place.

It kind of makes sense that critical financial infrastructure would be one of the things that doesn’t just run on AWS and accepts it goes down with everything else when us-east-1 goes down