There's no easy answer, but you should definitely model what happens when X goes down if you depend on X.
It may even be a rational decision to take the downtime if the cost of avoiding it exceeds the expected cost of an eventual downtime, but that's a business decision that requires some serious thought.
> It may even be a rational decision to take the downtime if the cost of avoiding it exceeds the expected cost of an eventual downtime, but that's a business decision that requires some serious thought.
that's at the root of all infrastructure decisions, not just web app tech stacks but even something like utility service. I think it gets lost on a lot of technology people because we love to work on big technical things. No one wants a boring answer like a couple webservers and postgres with a backup in a different datacenter when there's a wall of knobs and switches to play with at the hyperscalers.
It may even be a rational decision to take the downtime if the cost of avoiding it exceeds the expected cost of an eventual downtime, but that's a business decision that requires some serious thought.