Minimum requirement for Build purposes

I currently have a build setup using one of the CI solutions.
I’m trying to buy more machines to build using a commandline. (Like A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums)

My question is if I’m only going to build & package, would I even need a graphics card?
Is there a recommended spec for just doing the build & packaging. (I’ll never run the build on that machine.)