throwaway6920
You're being loose in your usage of 'data'. No one is talking about cached copies of an upstream, but you probably are.
Read the post mortem a bit more closely. They explicitly state that the control plane(s) source of truth lives in core, and that logs aggregate back to core for analytics and service ingestion. Think through the implications on that one.
Arguable, it's best to think of the edge as a buffering point in addition to processing. Aggregation has to happen somewhere, and that's where shit hit the fan.
Partially true in this case; I can't speak to modern CF (or won't, moreso) but a large amount of internal services were built around SQL db's, and weren't built with any sense of eventual consistency. Usage of read replicas was basically unheard of. Knowing that, and that this was normal, it's a cultural issue rather than an "oops" issue.
Flipping the whole DC data sources is a sign of what I'm describing; FAANG would instead be running services in multiple DC's rather than relying on primary/secondary architecture.
Speaking from personal experience, what you're claiming as 'good', for CF meant SRE- usually core- got stuck with trying to fix a fundamentally broken design that was known faulty- and called faulty repeatedly- but forced through.
Nothing about this is desirable or will end well.
This reckoning was known and raised by multiple SRE near a decade before this occurred, and there were multiple near misses in the last few years that were ignored.
The part that's probably funny- and painful- for ex-CF SRE is that the company will do a hard pivot and try to rectify this mess. It's always harder to fix after, rather than building for, and they've ignored this for a long while.