I too read that part of your post and paused. Your argument about it not being built into Linux is interesting because it gets down to what is Linux versus what is the distribution, etc. Which I don't think is worth getting into. The truth is I'm almost positive you rely on plenty of other core components not built into Linux proper. DNS caching is certainly available to you and if you don't have config mgmt or an immutable infrastructure model in place, I'd start considering it soon.