Oo--tricky. I'm on the fence about whether synonym updates should be happening to the read index or the write index. If it's the read index and someone is making synonym changes while we're doing one of our two-stage mapping-and-reindexing changes, then the changes they push to ES won't be in effect when we finish our mapping change.

I think I'd rather all synonyms changes were made to the write index so that it's confusing when the person fiddling with them is fiddling with them, but it'll eventually be correct rather than the person is fiddling with them and then eventually they're not in effect and unless someone is paying attention, we'd have no idea.

Maybe a better thing to do is have the admin page say, "YO! THE READ AND WRITE INDEXES ARE DIFFERENT! DO NOT PASS GO!"?