I have lxd containers already running that have everything the system needs.
When starting CI it's doing a DB SQL dump replacement which takes 1-2s to prep, self hosted github actions.
Its been very cheap to run OVH cloud with the newest and fastest AMD EPYC CPUs that have high single core speeds. Did this as it was cheaper than GCP spot to have these always on.
I'll run many always on lxd containers that all match with the same stacks. Add another one when needing to parallelize more