Is swap size still as relevant as it was a decade ago? On a host with 20G RAM, I'd imagine the likelihood of hitting swap being much lower.  Having a couple of G available just in case seems like a good idea, but I'm unsure if the old (Total RAM * 2)=swap equation still rings true. 

*does some quick internet sleuthing*

According to this article: https://www.cyberciti.biz/tips/linux-swap-space.html RedHat basically says that for CentOS server 7, a minimum of 4G is recommended.  The caveat to this is that if your system needs to hibernate/suspend-to-disk, in which case you'll want 1.5-2x RAM as swap in order to write in-use memory to disk.

-jason