# Fedora Ignition Approach for Bootc Installation

## Overview

Fedora CoreOS uses **Ignition** instead of traditional kickstart for system configuration and bootc installation. Ignition is a modern, JSON-based configuration system designed for immutable infrastructure and container-first deployments.

## Key Technical Concepts

### 1. Ignition vs Kickstart

| Aspect | Ignition | Kickstart |
|--------|----------|-----------|
| **Format** | JSON | Shell-like syntax |
| **Purpose** | Immutable infrastructure | Package-based installation |
| **Configuration** | Declarative | Imperative |
| **Container Support** | Native | Via `ostreecontainer` directive |
| **Modernity** | Modern, cloud-native | Traditional, legacy |

### 2. Ignition Configuration Structure

```json
{
  "ignition": {
    "version": "3.4.0"
  },
  "storage": {
    "disks": [
      {
        "device": "/dev/sda",
        "partitions": [
          {
            "label": "BIOS-BOOT",
            "number": 1,
            "size": 1024
          },
          {
            "label": "EFI-SYSTEM",
            "number": 2,
            "size": 268435456
          },
          {
            "label": "ROOT",
            "number": 3,
            "size": 0
          }
        ]
      }
    ],
    "filesystems": [
      {
        "device": "/dev/disk/by-partlabel/ROOT",
        "format": "xfs",
        "path": "/"
      }
    ]
  },
  "systemd": {
    "units": [
      {
        "name": "bootc-install.service",
        "enabled": true,
        "contents": "[Unit]\nDescription=Install bootc container\n[Service]\nType=oneshot\nExecStart=/usr/bin/bootc install to-disk /dev/sda\n[Install]\nWantedBy=multi-user.target"
      }
    ]
  }
}
```

### 3. Container Installation via Ignition

#### Method 1: Systemd Service
```json
{
  "systemd": {
    "units": [
      {
        "name": "bootc-install.service",
        "enabled": true,
        "contents": "[Unit]\nDescription=Install bootc container\n[Service]\nType=oneshot\nExecStart=/usr/bin/bootc install to-disk /dev/sda\n[Install]\nWantedBy=multi-user.target"
      }
    ]
  }
}
```

#### Method 2: Direct Container Pull
```json
{
  "storage": {
    "files": [
      {
        "path": "/etc/containers/registries.conf.d/bootc.conf",
        "mode": 420,
        "contents": {
          "source": "data:text/plain;base64,W1JlZ2lzdHJ5XQpsb2NhdGlvbj0icXVheS5pbyIKc2VjdXJlPWZhbHNlCg=="
        }
      }
    ]
  }
}
```

## Fedora CoreOS ISO Analysis

### ISO Structure
```
fedora-coreos-42.20250803.3.0-live-iso.x86_64.iso
├── coreos/
│   ├── features.json          # Installer capabilities
│   ├── igninfo.json          # Points to ignition.img
│   ├── kargs.json            # Kernel arguments
│   └── miniso.dat            # Minimal ISO data
├── images/
│   ├── ignition.img          # Ignition configuration
│   ├── initrd.img            # Initial ramdisk
│   ├── rootfs.img            # Root filesystem
│   └── vmlinuz               # Kernel
├── EFI/fedora/grub.cfg       # EFI boot configuration
└── isolinux/isolinux.cfg     # BIOS boot configuration
```

### Boot Configuration
- **Kernel arguments**: `coreos.liveiso=fedora-coreos-42.20250803.3.0 ignition.firstboot ignition.platform.id=metal`
- **Ignition integration**: `ignition.img` loaded as initrd
- **No kickstart references** in boot configuration

### Features Capabilities
```json
{
  "installer-config": true,
  "installer-config-directives": {
    "append-karg": true,
    "architecture": true,
    "console": true,
    "copy-network": true,
    "delete-karg": true,
    "dest-device": true,
    "fetch-retries": true,
    "ignition-file": true,
    "ignition-hash": true,
    "ignition-url": true,
    "image-file": true,
    "image-url": true,
    "insecure": true,
    "insecure-ignition": true,
    "network-dir": true,
    "offline": true,
    "platform": true,
    "preserve-on-error": true,
    "save-partindex": true,
    "save-partlabel": true,
    "secure-ipl": true,
    "stream": true,
    "stream-base-url": true
  },
  "live-initrd-network": true
}
```

## Ignition Configuration Examples

### 1. Basic Bootc Installation
```json
{
  "ignition": {
    "version": "3.4.0"
  },
  "storage": {
    "disks": [
      {
        "device": "/dev/sda",
        "wipeTable": true,
        "partitions": [
          {
            "label": "BIOS-BOOT",
            "number": 1,
            "size": 1024,
            "typeGuid": "21686148-6449-6E6F-744E-656564454649"
          },
          {
            "label": "EFI-SYSTEM",
            "number": 2,
            "size": 268435456,
            "typeGuid": "C12A7328-F81F-11D2-BA4B-00A0C93EC93B"
          },
          {
            "label": "ROOT",
            "number": 3,
            "size": 0,
            "typeGuid": "4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709"
          }
        ]
      }
    ],
    "filesystems": [
      {
        "device": "/dev/disk/by-partlabel/ROOT",
        "format": "xfs",
        "path": "/"
      }
    ]
  },
  "systemd": {
    "units": [
      {
        "name": "bootc-install.service",
        "enabled": true,
        "contents": "[Unit]\nDescription=Install bootc container\n[Service]\nType=oneshot\nExecStart=/usr/bin/bootc install to-disk /dev/sda\n[Install]\nWantedBy=multi-user.target"
      }
    ]
  }
}
```

### 2. Registry Authentication
```json
{
  "ignition": {
    "version": "3.4.0"
  },
  "storage": {
    "files": [
      {
        "path": "/etc/ostree/auth.json",
        "mode": 420,
        "contents": {
          "source": "data:text/plain;base64,ewogICJhdXRocyI6IHsKICAgICJxdWF5LmlvIjogewogICAgICAiYXV0aCI6ICI8eW91ciBzZWNyZXQgaGVyZT4iCiAgICB9CiAgfQp9"
        }
      },
      {
        "path": "/etc/containers/registries.conf.d/bootc.conf",
        "mode": 420,
        "contents": {
          "source": "data:text/plain;base64,W1JlZ2lzdHJ5XQpsb2NhdGlvbj0icXVheS5pbyIKc2VjdXJlPWZhbHNlCg=="
        }
      }
    ]
  }
}
```

### 3. Network Configuration
```json
{
  "ignition": {
    "version": "3.4.0"
  },
  "networkd": {
    "units": [
      {
        "name": "00-eth0.network",
        "contents": "[Match]\nName=eth0\n[Network]\nDHCP=yes"
      }
    ]
  }
}
```

## Advantages of Ignition Approach

### 1. Modern Design
- **JSON-based** - easy to generate programmatically
- **Declarative** - describes desired state, not steps
- **Immutable** - configuration is applied once
- **Cloud-native** - designed for modern infrastructure

### 2. Container Integration
- **Native container support** - no special directives needed
- **Registry authentication** - built-in support
- **Container runtime** - integrated by default
- **Bootc compatibility** - works seamlessly with bootc

### 3. Flexibility
- **Modular** - can combine different configuration sources
- **Extensible** - easy to add new configuration types
- **Versioned** - configuration format is versioned
- **Validated** - JSON schema validation

## Implementation for Debian

### Calamares Integration
1. **Generate Ignition JSON** from Calamares configuration
2. **Create custom module** for container installation
3. **Handle registry authentication** via Ignition
4. **Integrate with bootc** installation process

### debian-installer Integration
1. **Replace preseed** with Ignition configuration
2. **Add container runtime** to installer environment
3. **Implement Ignition parser** in installer
4. **Handle container installation** via systemd units

### Key Implementation Steps
1. **Study Ignition specification** and examples
2. **Design JSON generation** from user input
3. **Implement container installation** logic
4. **Handle registry authentication** and configuration
5. **Test with real bootc containers**

## Comparison: Ignition vs Kickstart vs Preseed

| Feature | Ignition | Kickstart | Preseed |
|---------|----------|-----------|---------|
| **Format** | JSON | Shell-like | Debian-specific |
| **Container Support** | Native | Via directive | None |
| **Modernity** | High | Medium | Low |
| **Flexibility** | High | Medium | Low |
| **Validation** | Schema-based | Runtime | Limited |
| **Cloud Integration** | Excellent | Good | Poor |
| **Immutable Design** | Yes | No | No |

## Tools and Resources

### CoreOS Installer
- **`coreos-installer`** - tool for creating custom ISOs
- **`butane`** - YAML to Ignition converter
- **`ignition-validate`** - configuration validator

### Configuration Examples
- **Fedora CoreOS examples** - official configuration samples
- **Butane configs** - YAML-based Ignition generation
- **Container installation** - bootc integration patterns

### Documentation
- [Ignition specification](https://coreos.github.io/ignition/)
- [Butane documentation](https://coreos.github.io/butane/)
- [CoreOS installer](https://coreos.github.io/coreos-installer/)

## Next Steps for Implementation

1. **Study Ignition examples** for container installation
2. **Design JSON generation** from user configuration
3. **Implement Calamares module** for Ignition support
4. **Create debian-installer** Ignition integration
5. **Test with real bootc containers** and registries

## Conclusion

The Ignition approach used by Fedora CoreOS is **more modern and suitable** for our Debian bootc-image-builder than traditional kickstart or preseed. Its JSON-based configuration, native container support, and immutable design make it ideal for container-first deployments.

Key advantages:
- **Easier to generate** programmatically
- **More flexible** than kickstart/preseed
- **Container-native** by design
- **Better suited** for modern infrastructure
- **Future-proof** approach

This makes Ignition the recommended approach for both Calamares and debian-installer integration in our Debian bootc-image-builder project.