Why active-active is not best practice in the data center, and shouldn’t be in the cloud either.
Last time we dove into a «Load Balancing 101» discussion we looked at the difference between architected for scale and architected for fail. The question that usually pops up after such a discussion is «why can’t I just provision an extra server and use it. If one fails, the other picks up the load»?
We call such a model N+1 – where N is the number of servers necessary to handle load plus one extra, just in case. The assumption is that all N+1 servers are active, so no resources are just hanging out idle and wasting money. This is also sometimes referred to as «active-active» when such architectures include a redundant pair of X (firewalls, load balancers, servers, etc… ) because both the primary and backup are active at the same time.
So it sounds good, this utilization of all resources and when everything is running rosy it can benefit in terms of improving performance, because utilization remains lower across all N+1 devices.