Earlier quoted context omitted.
I've seen "worker", "main", "parent/child", and "primary/replica" used as a replacement depending on the context.
I've heard complains from some in various tech industries that parent/child is non-inclusive. I'm not saying I think it should be changed, but doesn't the logic of the people advocating these changes demand that all terms be as inclusive as possible?
For that matter, "worker" implies something along the lines of "working class" or "unskilled laborer" which isn't all that friendly of a metaphor either. Kind of tough to think of a way to express "doesn't think for onesself, just takes orders" without being mean.