nbdmux 0.2.3

HTTP-controlled NBD-export multiplexer for a small lab (boot Linux images over the network with overlayfs+tmpfs writes)

nbdmux

HTTP-controlled NBD-export multiplexer for a small lab. Register local disk-image files as named NBD exports over an HTTP control plane; nbdmux keeps an nbd-server subprocess alive that serves all registered exports on a single TCP port. Targets nbd-client against that port from an initramfs and boot the image with overlayfs over tmpfs for writes (see bty's ramboot boot mode for the canonical consumer).

Designed as a peer to withcache: small lab, single sidecar container, no third-party Python deps. Operationally:

[ bty-web ] --HTTP--> [ nbdmux ]  --supervises-->  [ nbd-server ]
                          |                              |
                          |                            TCP 10809
                          |                              |
                          v                              v
                     SQLite state                  [ target's
                     (exports table)                nbd-client ]

Components

Path	What it is
src/nbdmux/server.py	The daemon. HTTP control plane + nbd-server subprocess management + operator UI
src/nbdmux/client.py	Stdlib-only Python client library for other tools
deploy/Containerfile	Single-image deploy (Python + nbd-server)
deploy/compose.yml	Reference compose stack

System dependency

nbdmux runs nbd-server (from the classical nbd project) as a subprocess. Install at the OS level:

# Debian / Ubuntu
sudo apt install nbd-server

# Fedora
sudo dnf install nbd

The container deploy bundles it. Also make sure the nbd kernel module + nbd-client are available on the consuming Linux box (the target you're booting); they're in the same nbd package.

Install

pipx install nbdmux            # or: uv tool install nbdmux

Run the daemon (development; the container deploy is the recommended production path):

nbdmux-server --data-dir ./data --port 4040 --nbd-port 10809

Register an image:

curl -X POST http://localhost:4040/exports \
     -H 'Content-Type: application/json' \
     -d '{"name": "debian-sysdev", "file": "/path/to/debian-sysdev.img", "readonly": true}'

Then on a target Linux box:

modprobe nbd
nbd-client <nbdmux-host> 10809 -name debian-sysdev /dev/nbd0
fdisk -l /dev/nbd0   # the .img's partition table

HTTP control plane

Method	Path	Body	Returns
GET	/exports	-	array of exports
POST	/exports	{name, file, readonly?: bool}	the new export
DELETE	/exports/{name}	-	204
GET	/healthz	-	ok
GET	/	-	operator dashboard

Auth

Single-tenant, server-signed cookie -- same pattern as withcache. Set NBDMUX_ADMIN_PASSWORD to gate the operator UI + the HTTP control plane. Unset = open with a startup warning.

The NBD port itself is unauthenticated (nbd-server's classical model); LAN-only assumption, firewall is the operator's responsibility.

License

BSD-3-Clause.