FAQ

Is it a drop-in replacement for ubuntu-latest? Close: the same Ubuntu, the runner, Docker and toolchains through setup-*. Jobs start recorded on one CPU, so add hypervise update-config --physical-cpus 4 --no-recording where you want speed instead.

Why can't recorded runs use several cores? On real hardware the order in which cores touch shared memory is a race that can't be recorded cheaply. We measured it: recording 4 cores would cost 1.6x to 16x. Instead, hypervise records one core at a time and gets parallelism from shards.

Does recording change how my tests behave? No. A recorded machine is an ordinary x86 PC to the guest. Timing differs (it runs a bit slower), as on any other machine.

What happens to flaky tests? A flaky failure is recorded like any other, and its recording reproduces it every time.

Can I bring my own image? Not yet. Custom images are planned.