Firecracker vs Xen Project Hypervisor

Firecracker is open-source virtualization software for running container and function workloads in lightweight microVMs. It uses Linux KVM hardware virtualization to isolate each workload and exposes only five emulated devices, a design intended to reduce attack surface. MicroVMs start in under 125 ms, add under 5 MiB of memory overhead each, and a host can create up to 150 per second while packing thousands onto one server. A RESTful API configures and starts the VMs, while rate limiters govern network and storage bandwidth and operations. The companion jailer adds Linux user-space security barriers. Firecracker supports Linux hosts and guests with kernel versions 4.14 and above, plus OSv guests, on production 64-bit Intel, AMD, and Arm CPUs with hardware virtualization. VM snapshots are supported, but GPU acceleration is not. It is free under Apache 2.0, with integrations including containerd, Kata Containers, and Fly.io.

Xen Project Hypervisor is a free, open-source type-1 hypervisor that runs multiple operating systems on one host. The project describes uses including server and desktop virtualization, IaaS, embedded systems, security applications, and hardware appliances. Linux is the most common control stack; NetBSD and FreeBSD are also named as host options. Xen’s microkernel design has a small memory footprint and restricts the interface exposed to guests. It can run a system’s main device driver inside a VM, allowing that VM to be restarted after a driver crash or compromise without affecting the rest of the system. On x86, fully paravirtualized guests can run without virtualization extensions. Listed capabilities include snapshots, nested virtualization, and GPU acceleration. The separate XAPI toolstack supports multi-host management, snapshots and migration, resource pools, storage migration, Open vSwitch, event tracking, upgrades, patching, and monitoring. Its built-in guest support and templates cover Windows and Linux. Downloads are source releases for building, packaging, and platform integration.