Cloud Hypervisor vs Firecracker

Cloud Hypervisor is a free, open-source virtual machine monitor written in Rust for modern cloud workloads. It runs modern Linux and Windows guests on Linux hosts with x86-64 or AArch64 architectures, using minimal hardware emulation. Operators can manage VM lifecycles through a REST API or command-line interface, with an optional D-Bus API. It supports snapshots, nested virtualization, paravirtualized devices, physical device passthrough, and live migration between hosts without interrupting VMs. Migration data can be encrypted using mutual TLS. The maker says direct kernel boot reaches userspace in less than 100 ms. The project is supported by Kata Containers for running secure containerized workloads and is governed openly as part of the Linux Foundation. It has no commercial plan or usage limits stated. Linux hosts need kernel 4.11 or later for required KVM functionality; kernel 5.6 is recommended for adequate performance. Packages for some popular Linux distributions are available through the Open Build Service. For help, the project points users to GitHub discussions or Slack, with GitHub issues for bug reports and a mailing list for broader discussion.

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.