# KubeSolo OS

An immutable, bootable Linux distribution purpose-built for [KubeSolo](https://github.com/portainer/kubesolo) — Portainer's ultra-lightweight single-node Kubernetes.

> **Status:** All 6 phases complete. Boots and runs K8s workloads. Portainer Edge Agent tested and connected.

## What is this?

KubeSolo OS combines **Tiny Core Linux** (~11 MB) with **KubeSolo** (single-binary Kubernetes) to create an appliance-like K8s node that:

- Boots to a functional Kubernetes cluster in ~35 seconds
- Runs entirely from RAM with a read-only SquashFS root
- Persists K8s state across reboots via a dedicated data partition
- Uses a custom kernel (6.18.2-tinycore64) optimized for containers
- Supports first-boot configuration via cloud-init YAML
- Performs atomic A/B updates with automatic GRUB-based rollback
- Signs update images with Ed25519 for integrity verification
- Exposes Prometheus metrics for monitoring
- Integrates with Portainer Edge for fleet management
- Ships as ISO, raw disk image, or OCI container
- Requires no SSH, no package manager, no writable system files

**Target use cases:** IoT/IIoT edge, air-gapped deployments, single-node K8s appliances, kiosk/POS systems, resource-constrained hardware.

## Quick Start

```bash
# Fetch Tiny Core ISO + KubeSolo binary
make fetch

# Build custom kernel (first time only, ~25 min, cached)
make kernel

# Build Go binaries
make build-cloudinit build-update-agent

# Build bootable ISO
make rootfs initramfs iso

# Test in QEMU
make dev-vm
```

Or build everything at once inside Docker:

```bash
make docker-build
```

After boot, retrieve the kubeconfig and manage your cluster from the host:

```bash
curl -s http://localhost:8080 > ~/.kube/kubesolo-config
export KUBECONFIG=~/.kube/kubesolo-config
kubectl get nodes
```

### Portainer Edge Agent

Pass Edge credentials via boot parameters:

```bash
./hack/dev-vm.sh --edge-id=YOUR_EDGE_ID --edge-key=YOUR_EDGE_KEY
```

Or configure via [cloud-init YAML](cloud-init/examples/portainer-edge.yaml).

## Requirements

**Build host:**
- Linux x86_64 with root/sudo (for loop mounts)
- Go 1.22+ (for cloud-init and update agent)
- Tools: `cpio`, `gzip`, `wget`, `curl`, `syslinux` (or use `make docker-build`)

**Runtime:**
- x86_64 hardware or VM (ARM64 cross-compilation available)
- 512 MB RAM minimum (1 GB+ recommended)
- 8 GB disk (for persistent data partition)

## Architecture

```
Boot Media (ISO or Disk Image)
  │
  ├── GRUB 2 bootloader (A/B slot selection, rollback counter)
  │
  └── Kernel + Initramfs (kubesolo-os.gz)
        │
        ├── switch_root → SquashFS root (read-only, in RAM)
        ├── Persistent data partition (ext4, bind-mounted)
        │     ├── /var/lib/kubesolo   (K8s state, certs, SQLite)
        │     ├── /var/lib/containerd  (container images)
        │     └── /etc/kubesolo        (node configuration)
        ├── Custom init (POSIX sh, staged boot 00→90)
        │     └── Stage 45: cloud-init (Go binary)
        ├── containerd (bundled with KubeSolo)
        └── KubeSolo (single-binary K8s)
```

### Partition Layout (Disk Image)

```
GPT Disk (minimum 8 GB):
  Part 1: EFI/Boot   (256 MB, FAT32)  — GRUB + A/B boot logic
  Part 2: System A   (512 MB, ext4)   — vmlinuz + kubesolo-os.gz (active)
  Part 3: System B   (512 MB, ext4)   — vmlinuz + kubesolo-os.gz (passive)
  Part 4: Data       (remaining, ext4) — persistent K8s state
```

See [docs/design/kubesolo-os-design.md](docs/design/kubesolo-os-design.md) for the full architecture document.

## Custom Kernel

The stock Tiny Core 17.0 kernel lacks several configs required for containers. KubeSolo OS builds a custom kernel (6.18.2-tinycore64) that adds:

- `CONFIG_CGROUP_BPF` — cgroup v2 device control via BPF
- `CONFIG_DEVTMPFS` / `CONFIG_DEVTMPFS_MOUNT` — automatic /dev node creation
- `CONFIG_MEMCG` — memory cgroup controller
- `CONFIG_CFS_BANDWIDTH` — CPU bandwidth throttling

Unnecessary subsystems (sound, GPU, wireless, Bluetooth, etc.) are stripped to keep the kernel minimal. Build is cached in `build/cache/custom-kernel/`.

## Cloud-Init

First-boot configuration via a simple YAML schema. All [documented KubeSolo flags](https://www.kubesolo.io/documentation#install) are supported:

```yaml
hostname: edge-node-01
network:
  mode: static
  address: 192.168.1.100/24
  gateway: 192.168.1.1
  dns:
    - 8.8.8.8
kubesolo:
  local-storage: true
  local-storage-shared-path: "/mnt/shared"
  apiserver-extra-sans:
    - edge-node-01.local
  debug: false
  pprof-server: false
  portainer-edge-id: "your-edge-id"
  portainer-edge-key: "your-edge-key"
  portainer-edge-async: true
```

See [docs/cloud-init.md](docs/cloud-init.md) and the [examples](cloud-init/examples/).

## Atomic Updates

A/B partition scheme with GRUB boot counter for automatic rollback:

1. Update agent downloads new image to passive partition
2. GRUB boots new partition with `boot_counter=3`
3. Health check verifies containerd + K8s API + node Ready → sets `boot_success=1`
4. On 3 consecutive boot failures, GRUB auto-rolls back to previous slot

Updates can be signed with Ed25519 for integrity verification. A K8s CronJob checks for updates every 6 hours.

See [docs/update-flow.md](docs/update-flow.md).

## Monitoring

The update agent exposes Prometheus metrics on port 9100:

```bash
kubesolo-update metrics --listen :9100
```

Metrics include: `kubesolo_os_info`, `boot_success`, `boot_counter`, `uptime_seconds`, `update_available`, `memory_total_bytes`, `memory_available_bytes`.

## Project Structure

```
├── Makefile               # Build orchestration
├── build/                 # Build scripts, kernel config, rootfs overlays
│   └── scripts/
│       ├── build-kernel.sh        # Custom kernel compilation
│       ├── fetch-components.sh    # Download components
│       ├── create-iso.sh          # Bootable ISO
│       ├── create-disk-image.sh   # A/B partition disk image
│       └── create-oci-image.sh    # OCI container image
├── init/                  # Custom init system (POSIX sh)
│   ├── init.sh            # Main init + switch_root
│   └── lib/               # Staged boot scripts (00-90)
├── cloud-init/            # Go cloud-init parser
├── update/                # Go atomic update agent
├── test/                  # QEMU-based automated tests + benchmarks
├── hack/                  # Developer utilities (dev-vm, SSH, USB)
├── docs/                  # Documentation
│   ├── design/            # Architecture design document
│   ├── boot-flow.md       # Boot sequence reference
│   ├── update-flow.md     # A/B update reference
│   ├── cloud-init.md      # Cloud-init configuration reference
│   └── deployment-guide.md # Deployment and operations guide
└── .gitea/workflows/      # CI/CD (Gitea Actions)
```

## Make Targets

| Target | Description |
|--------|-------------|
| `make fetch` | Download Tiny Core ISO + KubeSolo binary |
| `make kernel` | Build custom kernel (cached) |
| `make build-cloudinit` | Compile cloud-init Go binary |
| `make build-update-agent` | Compile update agent Go binary |
| `make rootfs` | Extract Tiny Core + inject KubeSolo |
| `make initramfs` | Pack initramfs (kubesolo-os.gz) |
| `make iso` | Create bootable ISO |
| `make disk-image` | Create A/B partition disk image |
| `make oci-image` | Package as OCI container |
| `make build-cross` | Cross-compile for amd64 + arm64 |
| `make docker-build` | Build everything in Docker |
| `make quick` | Fast rebuild (re-inject + repack + ISO) |
| `make dev-vm` | Launch QEMU dev VM (Linux + macOS) |
| `make test-all` | Run all tests |

## Documentation

- [Architecture Design](docs/design/kubesolo-os-design.md) — full research and technical specification
- [Boot Flow](docs/boot-flow.md) — boot sequence from GRUB to K8s Ready
- [Update Flow](docs/update-flow.md) — A/B atomic update mechanism
- [Cloud-Init](docs/cloud-init.md) — first-boot configuration reference
- [Deployment Guide](docs/deployment-guide.md) — installation, operations, troubleshooting

## Roadmap

| Phase | Scope | Status |
|-------|-------|--------|
| 1 | PoC: boot Tiny Core + KubeSolo, verify K8s | Complete |
| 2 | Cloud-init Go parser, network, hostname | Complete |
| 3 | A/B atomic updates, GRUB, rollback agent | Complete |
| 4 | Ed25519 signing, Portainer Edge, SSH extension | Complete |
| 5 | CI/CD, OCI distribution, Prometheus metrics, ARM64 | Complete |
| 6 | Security hardening, AppArmor, ARM64 RPi support | Complete |
| - | Custom kernel build for container runtime fixes | Complete |

## License

MIT License — see [LICENSE](LICENSE) for details.