What is a bare-metal server?
A bare-metal server is a physical machine rented whole, with no provider hypervisor between your software and the hardware.
Runtime runs every sandbox as a Firecracker microVM on dedicated servers it operates itself, so each one gets its own kernel without a second layer of virtualization underneath. A new sandbox ran its first Python command 221 ms after the create request at the median on Runtime's servers on 28 September 2026 (speed).
Bare metal against a virtual machine
| Question | Bare-metal server | Virtual machine |
|---|---|---|
| Who owns the hardware | You, for the rental period | Shared; the provider slices it |
| Hypervisor | Yours to install, or none | The provider's |
| Hardware features | All of them: /dev/kvm, performance counters |
Only what the provider passes through |
| Start time | Minutes to hours, when a machine is provisioned | Seconds to minutes |
| Billing | The whole machine, busy or not | The slice, usually by the second |
Why sandbox providers care
A microVM needs hardware virtualization, which Linux exposes as KVM. Nested
inside another provider's VM, that is often missing or slow. Firecracker's own
getting-started guide is direct about it: "EC2 only supports KVM on .metal
instance types", and the project runs its tests on those. So a sandbox service
built on microVMs either rents bare metal or owns servers.
Owning the servers also sets the price floor. A provider reselling another cloud's VMs pays that cloud's margin first; one running its own hardware can bill the CPU a sandbox uses rather than the vCPUs it holds, which is how Runtime charges $0.025 per active vCPU-hour (pricing).
What you get on Runtime
You do not rent the machine. You get a slice of it with its own kernel, enforced on the host: CPU, memory, disk and network rules are applied outside the guest (security). A paid sandbox takes up to 16 vCPUs and 64 GiB, pauses with its memory kept, and costs $0.03125 an hour at 2 vCPUs and 4 GiB while it waits.
Related
Sources
Checked 27 September 2026.