Re: Optional DR/Resiliency
So there's absolutely no way no how whatsoever that two systems on two sites can share workload in an active/active manner, not necessarily two (or more) identical systems, and if one site goes down the design can be such that only critical parts of the workload are continued on the remaining site(s),
Of course you can, but then you don't have 100% resilience, you only have resilience for those parts of the infrastructure you deem to be critical. This is the whole principle of Business Continuity Management. Decide what's important, decide what risks you need to protect against, work out what it will cost, and do the cost-benefit analysis. If you need 100% resilience, you need a duplicate site. I know of companies where their DR site is used for report generation, background processing, and other non-critical work. It takes the load off the primary, on the understanding that in a crisis that low-priority stuff gets canned so that the DR site becomes Production.