I'd prefer primary/replica, because it's both more descriptive and, because Microsoft uses it, is already familiar to a huge swath of techies.

Also carries none of the baggage of slavery.

My understanding is that master/slave more accurately describes the relationship than primary/replica does. A replica implies mirroring, but doesn't imply the other key components that differentiate it from the primary or master node.

I think leader/follower is just as accurate while carrying less baggage, but I could see people getting offended by those terms, too. Follower implies lack of autonomy, blind devotion as in a cult, a follower of a dictator like Hitler, power centered around a possible demagogue, etc.

If I were working on a new project I would probably not use "master/slave", because at that point it's trivial not to use it, but to ask an established project to change what they're doing for something so petty seems very silly.

Since antirez has said "all capitalism is slavery" would be funny if he changed it to 'master/employee'