I see that GitlabCI now offers free runners for even private repositories in gitlab.com which is great (powered by DigitalOcean). However it seems the default runner is installed in a CoreOS distro which spawns a docker "ruby:2.1" by default.
Is there a way to configure these runners to spawn a Ubuntu 16.04 LTS docker image instead?
Turns out that I can use any image name from the docker hub.
So I added this at the top of my .gitlab-ci.yml:
image: ubuntu:16.04