The infra VM's rootfs is ephemeral (rebuilt each boot), so the bottle
registry DB needs durable storage across restarts. Give the infra VM a
firecracker analogue of a docker volume: a host-side ext4 file attached as
a second virtio-block device (guest /dev/vdb), mounted at the control
plane's DB dir (/var/lib/bot-bottle, where host_db_path lives at
db/bot-bottle.db).
- firecracker_vm.boot/_config take an optional `data_drive` (a non-root,
RW second drive).
- infra_vm creates the volume on first use (`mke2fs` an empty ext4 at
<fc-cache>/infra/registry.ext4) and mounts /dev/vdb in the PID-1 init
before the control plane starts. It's a plain ext4 file, so
`sudo mount -o loop <path>` (VM stopped) inspects bot-bottle.db directly.
Verified on a KVM host: register a bottle, restart the infra VM (fresh
rootfs, same volume) — /dev/vdb re-mounts and the registry `db/` dir + a
marker file survive the restart.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck
didericis
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