I don't think that's true, in the usual sense of the term. When a replica is used as a read slave, that introduces problems with (strong) consistency, that def

I don't think that's true, in the usual sense of the term. When a replica is used as a read slave, that introduces problems with (strong) consistency, that definitely starts to resemble any other distributed system. Adding automated failover adds the need for some kind of consensus algorithm, another feature of distributed systems. However, if failover is manual, for example, then 2 nodes can be nearly indistinguishable from 1 node, if no failover occurs. It also strains the definition of "distributed" if both nodes are adjacent, possibly even with direct network and/or storage connections to each other.