[pm90]

> Of course, to make them fully independent, you have to replicate everything, so you wind up buying several redundant copies of your system...

Yeah, and keeping around warm systems ready to failover in case of a zonal outage seems like a preposterous waste of resources.

The alternative... to keep around multiple replicas of your system in different zones, all ready to accept traffic and which do serve traffic, seems more practical and less wasteful.

[erik_seaberg]

This. Paying for n+2 capacity is really expensive when n=1, but pretty reasonable at n=5 or n=10. Until someone gouges you on data transfer …

[satanspastaroll]

It's not a waste when it serves a purpose. Availability is a big concern

[pm90]

Sure, from the perspective of availability, it makes sense to keep this around. The US military has redundancies in place to handle many kinds of adverse scenarios, which comes at a price, but is justifiable. The point I'm trying to make is that if availability is the _only_ value, it becomes hard to justify that if you're a scrappy for-profit corp looking at your bottom line.

If instead of availability being the only value, there would be a more value provided from actually using such resources, more folks would adopt cross-AZ architectures which would be a win-win for both the customer (get HA for lower or no cost and go down less often and succeed in the market) and thus the cloud provider (keep raking in the steady cloud revenue as the customer grows).