Apple · encore.dev
encore.dev Rebuilt the Linux MicroVM Stack on Apple Silicon
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Key facts
- On Linux, each VM is a separate firecracker child process, driven over its REST API on a Unix socket by a small HTTP/1.1 client written for that limited API surface
- Encore builds and deploys backend applications, and since mid-2022 every one of those builds has run inside a Firecracker microVM
- The setup worked, which is why it lasted from 2022 until they finally replaced it
- The team looked at what already existed first, and running Linux in a VM on macOS has several working implementations: Apple's own container reached 1.0 this June, Lima and Tart have been doing it
Summary
Encore builds and deploys backend applications, and since mid-2022 every one of those builds has run inside a Firecracker microVM. Firecracker drives KVM, so it needs a Linux host with /dev/kvm, which no Mac has, and most engineers at Encore develop on a Mac. So for four years, working on the build system meant working on it somewhere else. The team onboarded each engineer with a script you ran once. Getting a change onto that environment took a second script, which read your username and your port out of the CUE config, from a gitignored per-engineer file, because they all shared that host and had to agree not to collide.