- as a guy not familiar or in loop with all these sandbox products, i have a quick question for anyone reading this

- what is the difference between docker and modal?

- what does modal do that docker doesnt?

- what is the cold start time comparison between both?

- how do both of these differ from something called "Firecracker VM"?

I can describe firecracker.

With Intel VMX virtualization, instruction execution is handled by the CPU but (a lot) of software still has to deal with HW peripheral emulation .

QEMU uses KVM (Intel VMX, etc) but implements HW peripherals (display, network, disk, etc) faithfully matching really HW and provides a full BIOS (SeaBios) or UEFI firmware (EDK) to deal with with boot process.

Over time, Linux (and Windows) were extended to support novel “peripherals” designed for high emulation performance (not a real HW product).

Firecracker basically skips all the “real” peripheral emulation and skips the full BIOS/UEFI firmware. Instead, it implements just enough to boot modern Linux directly. Also written in Rust instead of C. It will never support DOS, Windows 95 or probably anything else.

The “microVM” BIOS allows it to start booting Linux very quickly (sub-second). A traditional QEMU VM might take 2-5 seconds. Some people are emboldened to effectively move back from containers to running applications in a VM…

Instead of the VM being long lived, it is really just for running a single app.

I think Kata containers had this idea for much longer but Firecracker provides a more efficient implementation for such a thing.