Variable macOS Spin-up times 

Slightly longer spin up times can occasionally occur with the macOS executor due to the way pre-scaling works. CircleCI automatically spins up a certain number of macOS VMs per image/resource class combination and the exact number varies depending on the demand we are seeing. Pre-scaling is always adjusting based on current demand and capacity availability, but it is not always able to predict spikes in demand.

If your job request can be fulfilled by a VM that is already booted up and ready to go, then you will see a very short spin up time - usually less than 30 seconds.

If, however, we do not have any VMs available at the time of the request, then we need to spin up a new VM and this can take up to a few minutes. Generally this is more likely to happen if you are using a less popular image/resource class combination as CircleCI will be pre-booting less of these.

This is normal behavior and is something we constantly monitor closely. We cannot guarantee that there are enough pre-booted VMs for every job, but we do try to ensure this is the case as much as we can to provide a better customer experience.

Excessively Long Spin-up Times

If you find your jobs are consistently taking an excessive amount of time to spin up (more than five minutes), then please reach out to us on a support ticket so we can look into this further.