VirtualBox runner doesn't start multiple instances
We are trying to configure a build server using the gitlab-ci-multi-runner to use virtualbox to configure multiple build agents (runners). We have read the documentation and can't see a way to get it to run, say, 3 VMs. We need all of the VMs to use the same base disc image, and assumed that through snapshots the behaviour would be that it attempt to create additional VMs until it runs out of RAM, for example.
Is this behaviour by design? If so is there a way we can configure multiple VMs to run within the VirtualBox runner?
Has consideration been given to an option to allow multiple runner VMs to be created, e.g. the ability to specify say 3 runners?
We appreciate that docker is the preferred mechanism for build servers, but unfortunately it has a number of blocking issues that prevent us from using it, namely: