COCompuIves·Feb 28, 2023
At CodeSandbox we use Firecracker to run our VMs (more info here: https://codesandbox.io/blog/how-we-clone-a-running-vm-in-2-s...).
To answer the questions:
> what version of the kernel do you use (the github page says 5.10 but isn't that quite old?)
Right, they have tested with 5.10, but it also works with higher kernel versions. Our host currently runs 5.19 and we're planning to upgrade to 6.1 soon. The guest runs 5.15.63, we use a config very similar to the recommended config by FC team (it's in the FC repo). It's important to mention that we had to disable async pagefaulting (a KVM feature) with more modern kernel versions, as VMs could get stuck waiting for an PF resolve.
> What do you use to build the 'micro' images
We created a CLI that creates a rootfs from a Docker image. It pulls the image, creates a container and then extracts
Read the rest
the fs from it to an ext4 disk. For the init, we forked the open sourced init from the Fly team (https://github.com/superfly/init-snapshot) and changed/added some functionality.
> How do you keep timesync of you're not using a timesync daemon?
IIRC we expose the time as a PTP device (handled by kvm) and run phc2sys to sync the time in an interval. Firecracker has some documentation on this, where it recommends chrony. It can also be done with vsock, but it would be more manual.
> Handle kernel and app logs without adding an log daemon, and same through vsocks, etc?
The init forwards stdout/stderr of the command it runs to its own stdout, which Firecracker then logs out by itself. A supervisor reads these and writes the logs to files.