[transect]

We use preemptibles for our CI fleet and it's great. We can run a hundred instances at full tilt boogie for 8 hours a day and the nodepool downscales to zero while we sleep. It's a no brainer if your controller (and use case) can handle preemption gracefully.

[__float]

What CI software do you use? I played around with spot instances and Jenkins, and it was quite a poor experience.

[transect]

We use Jenkins to invoke Tekton pipelines (https://github.com/tektoncd/pipeline) with a wrapper we wrote. The pipeline runs, outputs junit to a bucket and we pull it back and give it to jenkins. Was a bit of a lift to get working out of the gate but it's been mostly smooth (and flexible and cheap) since then.