Got a new server that is mainly going to be used for development tools: Gitlab, Docker, and others. Anyone here have any suggestions on how to set it up? Should we virtualize it or use Docker on top of a light OS light Core OS?

Virtualise everything! If you can makes transferring between hardware simples

I'd install a server OS like Centos, configure it with Ansible Playbooks, and run services in Docker containers. Most stable, reproducible, maintainable, and resource efficient way of doing things.

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my vote would go for virtualise everything.

But I have never used docker so I can't really say if that way would be better :)

i tried docker yesterday and found it awesome. In under 3 Minutes you have a pre configured webserver running.
I'm thinking about to buy a www.up-board.org (a raspberry pi with an x86 intel atom) and install RancherOS on it for playing around.