Primary/Replica is often used in databases.
Distributed databases where by nature that often can change had already often adopted the terminology used by consensus algorithms, which typically speak of a "leader" (that's choosen out of "nodes", "members", "servers" by "leader election" of some kind. Sometimes "follower" for the non-leader nodes)
Primary/Secondary is an option.
In electronics there is the suggestion of Controller/Peripheral
These are all fairly common terms I see or use for these scenarios.
There are a other terms you could use though in different systems that make sense.
Bust out a thesaurus. Ace is apparently close to master. I kinda like that word. Ace of database.