Recently, I activated a very small VPS: 512MB RAM, 20GB SSD drive space. It ran WordPress well under Fedora 27. However, I encountered a problem with DNF refusing to update, exiting with a kernel panic on the executable.
Turns out that a virtual server image with minimal OS config can be born without a swap file. I found this link to be useful (note that for this subsystem Fedora 27 is close enough to CentOS 7, which itself is Fedora 19):
https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-centos-7