this is easy and doable if your change is a front end change.

good luck trying this when its a backend change involving distributed threads, locks, resources, etc where production load is 100x more than staging/test.

If the cost of downtime is high enough you can mirror some or all traffic onto a shadow copy of the infrastructure.

Obviously in those cases, you’d take more than a minute to review prior to deployment...

There are plenty of backend changes where your list of complexities do not apply.

what would be some good resources to learn how to build such infrastructure? I've seen it as a feature of various platforms but would imagine it could become complex otherwise.

It wouldn’t be practical without some kind of underlying infrastructure orchestration system. Obviously some companies have gone the extra step to actually build these systems - e.g. Google made Kubernetes. For any not-huge companies, I think it pretty much just falls to choosing one of the many existing tools.

Obviously it is possible to just throw together a bunch of scripts and vaguely make it all happen, I’m not sure I’d be comfortable to do that in production.

The simple way to do this can apply if you're mostly doing things in the context of a user. Write the change to check if a hash of the user identifier is less than a target; increase the target over time.