Knuckle

A modern, interactive TUI "installer" for Flatcar Container Linux, designed for bare-metal deployments. Not a real installer because making one would be dumb. It's a form that makes a valid ignition file and passes it to the installer. We're just making users not have to use ignition, with an ubuntu-server style install UX.

This is also basically Azure Container Linux (Home Edition).

Why

Flatcar is typically provisioned in cloud environments via Ignition configs. Bare-metal installations lack a polished setup experience. Knuckle bridges this gap with an intuitive terminal wizard that generates Ignition configurations and executes the installation.

Status

Feature-complete. All 9 TUI steps are implemented, with 214 tests passing (race-clean).

Features

• 9-step guided wizard — Welcome → Network → Storage → User → Sysext → Update Strategy → Review → Install → Done
• Channel selector with version details — shows kernel, systemd, docker, containerd, ignition, and etcd versions per channel (sourced from version.txt, package lists, and rootfs-included-sysexts)
• Hardware probing — automatic disk and network interface discovery with /dev/disk/by-id path resolution
• Network configuration — DHCP or static IPv4
• User setup — hostname, timezone, password (bcrypt hashed), GitHub SSH key fetching with multi-key support
• System extensions — version-pinned sysext catalog fetched from GitHub Releases API (flatcar/sysext-bakery)
• Update strategy — reboot, off, or etcd-lock options
• Review screen — full Butane YAML preview before install
• Install step — progress bar, wraps flatcar-install for disk provisioning
• Ignition generation — produces valid Ignition JSON via Butane (Flatcar variant)
• ISO generation — internal/iso package for creating installer ISOs
• Config validation — consistency checks before install
• Dry-run mode — --dry-run flag skips all disk writes
• Ctrl+C double-press — confirmation before quitting

Support Matrix

Dimension	Supported
Architecture	x86_64
Storage	Single target disk
Networking	DHCP, static IPv4
Language	English
Sysexts	Official Flatcar Bakery (via GitHub Releases API)
Config mode	Guided OR external Ignition URL (mutually exclusive)

Quick Start

# Build from source
go build ./cmd/knuckle

# Run the installer (on a Flatcar live environment)
./knuckle

# Dry-run mode (no disk writes)
./knuckle --dry-run

Development

# Build and test
go build ./cmd/knuckle
go test -race ./...

# Full CI pipeline (tidy + lint + test + build)
just ci

# VM testing — boots QEMU with Flatcar, deploys binary, SSH on port 2222
just vm

# SSH into the running VM
just ssh

# Build a self-contained installer disk image
just installer-disk

Requires: Go 1.26+, just, golangci-lint

VM Testing

just vm downloads a Flatcar stable QEMU image, cross-compiles knuckle for linux/amd64, boots a VM with two disks (boot + target), and launches knuckle over SSH with --dry-run. SSH is forwarded on 127.0.0.1:2222. The TUI requires a PTY (the SSH -t flag handles this).

Architecture

cmd/knuckle/         → CLI entrypoint
internal/bakery/     → sysext catalog client (GitHub Releases API)
internal/github/     → GitHub API client (SSH keys, releases)
internal/ignition/   → Butane/Ignition config generation
internal/install/    → flatcar-install orchestration
internal/iso/        → ISO image generation
internal/model/      → shared data model
internal/probe/      → system probing (lsblk, ip, udevadm)
internal/runner/     → command execution wrapper (supports --dry-run)
internal/tui/        → Bubble Tea view models (9 steps)
internal/validate/   → input and config validation
internal/wizard/     → step flow state machine

Key Design Decisions

• Sysext catalog comes from the flatcar/sysext-bakery GitHub Releases API, not from flatcar.org directly
• Channel versions are assembled from three sources: version.txt (kernel, systemd), package lists, and rootfs-included-sysexts (docker, containerd — these are sysexts since Flatcar 4081+, not base image packages)
• Password hashing uses bcrypt, computed client-side before Ignition generation

Tech Stack

• Go 1.26+
• Bubble Tea v2 — TUI framework
• Lip Gloss v2 — styling
• Huh v2 — form inputs
• Bubbles v2 — reusable components
• Butane v0.27 — Ignition config compilation
• flatcar-install — disk provisioning

License

Apache 2.0