Some people might want to use Gitlab’s support for spinning up CI runners on DigitalOcean, and may want to test their application on IPv6… Well, Docker, by default, does not do IPv6: you have to add --ipv6=true to the daemon, and add some CIDR that Docker may hand out (e.g. fixed-cidr-v6='fc00::d0c:0:0:0:1/64').

If you’re okay with link local IPv6, you can use these options in your Gitlab Bastion:

    MachineOptions = [
"digitalocean-image=coreos-stable", # The DigitalOcean system image to use by default
"digitalocean-ssh-user=core", # The default SSH user

The trick is to pass an extra = between engine-opt and the option itself, otherwise Docker Machine interprets 'engine-opt ipv6=true' as a standalone option, instead of 'engine-opt' as option and 'ipv6=true' as parameter.