Definition of Availability

[jpcs]

When Gilbert and Lynch proved the CAP theorem they did it by relying on a very tight definition of availability, that included the condition that all nodes in the distributed system should be able to respond to a request in a finite amount of time. Importantly this excludes a typical high availability solution like failover to a replica, where the minority partition becomes unavailable but the distributed system as a whole can still respond to requests.

I think it's important to include this information prominently in your (otherwise very good) CAP write up, as it starts to show why the CAP theorem (as proved) often is not relevant to real world distributed systems.