Switching away from problematic terminology is also a good opportunity to make it more accurate and specific. In some situations it's "process A allows writes,

Switching away from problematic terminology is also a good opportunity to make it more accurate and specific. In some situations it's "process A allows writes, process B only allow reads", in which case "writer/reader" maybe? In other situation it's "process A is in control, but process B will take control if process A fails". In which case "controller/fallback", maybe?