DNS broke after resizing server and upgrading packages. How can I fix it?

I just resized my server and then did sudo apt-get upgrade to update my packages, and now my server’s DNS is totally borked:

ping google.com
ping: unknown host google.com

My resolv.conf is totally empty:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

I can edit my resolv.conf to fix the problem, but then my edits get blown away upon reboot and goes back to being empty.

What can I do to fix this? What more information can I provide?

Thanks!