# banger

Minimal Firecracker launcher.

## Requirements
- Linux host with KVM (`/dev/kvm` access)
- `sudo`, `ip`, `curl`, `ssh`, `jq`
- `dmsetup`, `losetup`, `blockdev` (device-mapper snapshot for rootfs)
- `e2cp`, `e2rm` (writes hostname and resolv.conf into rootfs snapshot)

## Files
- `firecracker`: Firecracker binary
- `vmlinux`: guest kernel
- `rootfs.ext4`: guest root filesystem
- `id_ed25519`: SSH key for `root`

## Run
```
./run.sh
```

## Run Options
```
./run.sh --name calm_otter --vcpu 4 --ram 2048 --home-size 6G
```
- `--name`: must be unique and match `[a-z0-9][a-z0-9-]{0,63}`.
- `--vcpu`: defaults to 2, max 16.
- `--ram`: MiB, defaults to 1024, max 32768.
- `--rootfs`: path to the rootfs image (default: `./rootfs-docker.ext4`).
- `--kernel`: path to the kernel image (default: `./wtf/root/boot/vmlinux-6.8.0-94-generic`).
- `--initrd`: path to the initrd image (default: `./wtf/root/boot/initrd.img-6.8.0-94-generic`).
- `--home-size`: M/G suffixes supported (default: 2G).
- `--var-size`: M/G suffixes supported (default: 2G).

## Storage Layout
- `rootfs.ext4` is used as the read-only origin for a per-VM device-mapper snapshot mounted as `/`.
- Each VM gets writable ext4 disks mounted at `/home` and `/var`.
- The base image must include `/etc/fstab` entries for `/dev/vdb` → `/home` and `/dev/vdc` → `/var`.
- `/run` and `/tmp` should be tmpfs via `/etc/fstab`.

## SSH
```
ssh -i "./id_ed25519" root@<guest_ip>
```

## Internet Access
VMs do not get internet access by default. You must enable forwarding and NAT:
```
./nat.sh up <id-or-name-prefix>
```
This enables `net.ipv4.ip_forward=1` and installs per-VM NAT rules for the VM's
guest IP and TAP device. To remove rules:
```
./nat.sh down <id-or-name-prefix>
```
Check status with:
```
./nat.sh status <id-or-name-prefix>
```

## Shutdown
```
reboot
```

## Customize Rootfs (Docker + Kernel Modules)
Use `customize.sh` to build a writable rootfs with Docker and kernel modules
preloaded so Docker works out of the box.

```
./customize.sh rootfs-docker.ext4 --size 6G --docker
```

Options:
- `--size`: optional size for the output image.
- `--kernel`: kernel path (default: `./wtf/root/boot/vmlinux-6.8.0-94-generic`).
- `--initrd`: initrd path (default: `./wtf/root/boot/initrd.img-6.8.0-94-generic`).
- `--modules`: kernel modules directory (default: `./wtf/root/lib/modules/6.8.0-94-generic`).
- `--docker`: install Docker packages into the image.

After boot, enable NAT and validate Docker:
```
./nat.sh up <id-or-name-prefix>
ssh -i "./id_ed25519" root@<guest_ip> "systemctl enable --now docker"
ssh -i "./id_ed25519" root@<guest_ip> "docker run --rm hello-world"
```

## Build Rootfs On Demand
`run.sh` defaults to `./rootfs-docker.ext4`. If it is missing, `run.sh` will
invoke `make-rootfs.sh` to build it.

```
./make-rootfs.sh
```

`make-rootfs.sh` chooses the first available base image:
- `./rootfs.ext4`
- `./ubuntu-noble-rootfs/rootfs.ext4`
- `./ubuntu-lts/rootfs.ext4`

## VM Info File
Each VM writes:
- `state/vms/<id>/vm.json`: raw `/vm/config` response from Firecracker.
- `state/vms/<id>/meta.json`: local metadata (id, name, pid, created_at, guest_ip, tap, api_sock, log, rootfs, kernel, snapshot info).

## Log Notes
- `PCI: Fatal: No config space access function found` and `MissingAddressRange` lines are expected with `pci=off` in `run.sh`.
- `SELinux: Could not open policy file ...` is expected in the minimal rootfs.