Hello I'd like to develop a "something" (app/module/patch/whatever) that gets run whenever something is changed in the DNS. Specifically, I'd need to TSIG-update *some* records on external DNS servers (that I can't make slaves) when the corresponding internal record is changed. I'd prefer having "synchronous" updates so both internal and external servers won't return conflicting answers. Any hint about where to start? Are there some docs available? TIA.