Jan Novak
640bf5065a
A "poor man's" Firecracker VM orchestrator that boots a single golden VM,
snapshots it, then restores N clone VMs from that snapshot with minimal
per-clone overhead.
How it works:
- `init` — downloads a Linux 6.1 kernel and builds a minimal Alpine 3.20
rootfs (512 MiB ext4) with a basic init script
- `golden` — boots the golden VM, lets it settle, then pauses and snapshots
it (vmstate + memory file); the golden VMM is then terminated
since only the artifacts are needed
- `spawn N` — restores N clone VMs concurrently from the golden snapshot:
* rootfs: filesystem-level COW copy via `cp --reflink` (falls
back to a plain copy if reflinks are not supported)
* memory: shared golden `mem` file; Firecracker's MAP_PRIVATE
lets the kernel handle COW page-by-page at no up-front cost
* vmstate: small file, cheap regular copy per clone
* networking: per-clone TAP device (fctapN) bridged to fcbr0
with iptables MASQUERADE NAT on the default route interface
- `status` — reads PID files and checks /proc to report alive/dead clones
- `kill` — stops in-memory clones, kills any stragglers via PID files,
and tears down all fctap* devices
- `cleanup` — kill + remove all state dirs and the bridge
All tunables (binary path, base dir, kernel/rootfs paths, vCPUs, memory,
bridge name/CIDR) are configurable via environment variables.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
// fc-orchestrator — Poor man's Firecracker snapshot orchestrator in Go.
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//
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// Creates a golden VM, snapshots it, then spawns N clones that share the
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// base memory file via Firecracker's MAP_PRIVATE (kernel-level COW).
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// Rootfs gets a filesystem-level COW copy (reflink where supported).
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//
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// Usage:
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//
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// go build -o fc-orch .
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// sudo ./fc-orch init
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// sudo ./fc-orch golden
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// sudo ./fc-orch spawn 10
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// sudo ./fc-orch status
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// sudo ./fc-orch kill
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// sudo ./fc-orch cleanup
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package main
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import (
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"fmt"
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"os"
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"github.com/you/fc-orchestrator/orchestrator"
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)
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func main() {
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if len(os.Args) < 2 {
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usage()
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os.Exit(1)
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}
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orch := orchestrator.New(orchestrator.DefaultConfig())
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switch os.Args[1] {
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case "init":
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fatal(orch.Init())
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case "golden":
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fatal(orch.Golden())
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case "spawn":
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n := 1
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if len(os.Args) > 2 {
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fmt.Sscanf(os.Args[2], "%d", &n)
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}
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fatal(orch.Spawn(n))
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case "status":
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orch.Status()
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case "kill":
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fatal(orch.Kill())
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case "cleanup":
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fatal(orch.Cleanup())
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default:
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usage()
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os.Exit(1)
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}
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}
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func usage() {
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fmt.Fprintf(os.Stderr, `Usage: %s <command> [args]
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Commands:
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init Download kernel + create Alpine rootfs
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golden Boot golden VM → pause → snapshot
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spawn [N] Restore N clones from golden snapshot (default: 1)
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status Show running clones
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kill Kill all running VMs
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cleanup Kill VMs + remove all state
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Environment:
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FC_BIN firecracker binary path (default: firecracker)
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FC_BASE_DIR working directory (default: /tmp/fc-orch)
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FC_KERNEL vmlinux path
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FC_ROOTFS rootfs.ext4 path
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FC_VCPUS vCPUs per VM (default: 1)
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FC_MEM_MIB MiB per VM (default: 128)
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FC_BRIDGE bridge name or "none" (default: fcbr0)
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`, os.Args[0])
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}
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func fatal(err error) {
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if err != nil {
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fmt.Fprintf(os.Stderr, "fatal: %v\n", err)
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os.Exit(1)
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}
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}
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