Reliability: It’s not great

> This is a theme. Existing open source is not designed for global deployment

Eh? Unless you are consuming something as a service and it actually advertises it as a feature, nothing is ready for 'global deployment'.

If you have a 'centralized' secret storage, then you have made it tied to a region. Want to have redundancies and lower latency? You'll have to distribute it. Vault has docs about this: https://developer.hashicorp.com/vault/tutorials/day-one-raft...

This one is interesting because Vault has an enterprise product which I assume (hope?) Fly is paying for. That enterprise version includes performance replicas, which allows for cross-region replication of secrets with region-local reads (and slightly lower writes). The OP almost makes it sound like they are using the non-enterprise versions (or at the very least, not taking advantage of this particular functionality).

That said, I'd imagine with large enough scale, these sorts of features break anyways.