If I rent a dedicated machine I can certainly do what I described there[0] by hand but would you envision having some kind of turn-key support for GitLab CI runners, supporting both gitlab.com through some partnership and self-hosted instances? That would be brilliant, especially considering Xcode integration with GitLab.
CI/CD product manager from GitLab here. We're actually already looking at adding this - we're starting with some experimentation in our internal item at https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues.... Some folks here at GitLab already have this set up and working at a small scale, so it's certainly possible (with a couple caveats.)
Haha seems like you ran into the exact same issues as I did! It works brilliantly with a concurrency of 2 on an early 2015 2-core i5 13" MBP with 16GB of RAM, and I'm even using the machine interactively while builds are processed. I'm using Sierra as a base but I've been building Mavericks, El Capitan and High Sierra ones too. VMs are 1 CPU / 4GB. I saw no gain in bumping up VMs to 2 CPUs.
Wanted to share that we developed a GitLab CI Runner/executor for Anka Build and have made it public (It was done for one of our user). It basically enables you to run your iOS/macOS GitLab CI pipelines/jobs on Anka build macOS cloud. You can configure Anka Build macOS cloud on-prem(on macs) or on hosted macs. Happy to share more details.https://github.com/veertuinc/gitlab-runner
[0]: https://news.ycombinator.com/item?id=18404893
[1]: https://about.gitlab.com/2018/06/06/one-click-clone-to-xcode...