VoiceStudio/docs/remote-gpu.md

Remote GPU backend

Run the OmniVoice backend on one machine (a GPU box, a home server) and drive it from the desktop app or a browser on another — over your tailnet, with the inference staying on the powerful machine.

This is opt-in and off by default: with no API key set, the backend stays loopback-only exactly as before.

The shape

┌──────────────┐     tailnet (WireGuard)      ┌─────────────────────┐
│ laptop        │  ws/https to MagicDNS URL   │ gpu-box              │
│ OmniVoice UI  │ ──────────────────────────▶ │ OmniVoice backend    │
│ (thin client) │  Authorization: Bearer …    │ OMNIVOICE_API_KEY set │
└──────────────┘                              └─────────────────────┘

The desktop app is the thin client — there is no separate binary. You set a Backend URL and an API key in Settings, and every request (including the dictation and TTS WebSockets) is sent to the remote with the key attached.

1. On the GPU box: run the backend with a key

Generate a key and start the backend with it set:

export OMNIVOICE_API_KEY="$(python -c 'import secrets; print(secrets.token_urlsafe(24))')"
export OMNIVOICE_SERVER_MODE=1          # headless: relaxes the loopback admin gate
uv run uvicorn backend.main:app --host 0.0.0.0 --port 3900

The Docker image is the same idea — pass -e OMNIVOICE_API_KEY=….

When OMNIVOICE_API_KEY is set, every non-loopback HTTP and WebSocket request must present it, as Authorization: Bearer <key>, ?api_key=<key> (browser WebSockets can't set headers), or the ov_key cookie the backend sets after the first authenticated request. Loopback traffic on the box itself is never gated, so local tools keep working.

2. Reach it over Tailscale

Install Tailscale on both machines (its client is BSD-3 open source; self-host the control plane with headscale if you want a fully open stack). Then the box is reachable at its MagicDNS name:

http://gpu-box.your-tailnet.ts.net:3900

For TLS (recommended — see the warning below), put the port behind Tailscale Serve on the box:

tailscale serve 3900
# now reachable at https://gpu-box.your-tailnet.ts.net

Serve terminates on the node and forwards from 127.0.0.1, so to the backend the request looks like loopback — which is why the API key is still required in that path (the bearer gate doesn't rely on the source address for non-local exposure; set the key and it always applies to keyed clients).

Do not use tailscale funnel (public-internet exposure) for this. Even with a key, a voice-cloning backend should not be on the open internet.

3. In the app: point at the remote

Settings → Sharing → Remote backend:

• Backend URL: the MagicDNS URL from step 2 (with :3900 if you didn't use Serve, or no port if you did).
• API key: the value of OMNIVOICE_API_KEY from step 1.
• Test connection hits {url}/health and shows the remote's version and device.
• Save & reload stores both in this browser/app and restarts the UI against the remote. The URL must be a full http:// or https:// URL (gpu-box:3900 alone is rejected), and saving a URL that hasn't passed Test connection asks for confirmation first — a wrong base would leave the app unable to reach any backend until you change it back here.

Leave the URL empty to go back to the local backend.

From a browser (no desktop app)

You can also drive the remote from a plain browser — open the URL with the key in the fragment once:

https://gpu-box.your-tailnet.ts.net/#api_key=<key>

Use the fragment (#, not ?) deliberately: fragments are never sent to the server, so the key stays out of the GPU box's and any reverse proxy's request logs. The key is stored for that browser and the fragment is scrubbed from the address bar (so it doesn't linger in history or get re-applied on a reload). If your key contains +, &, #, or =, URL-encode it (e.g. #api_key=a%2Bb); keys from secrets.token_urlsafe (above) need no encoding. Thereafter the UI loads normally with the key attached to every request. If a request ever 401s again (wrong/rotated key), you're prompted to re-enter it. The same gate shows a LAN-share PIN prompt instead when network sharing — not a remote key — is what's gating access.

Security notes

• Plain HTTP is sniffable. A bearer key over http:// on a hostile network can be read off the wire. Use Tailscale (WireGuard-encrypted) or Tailscale Serve (TLS) for anything beyond a fully trusted LAN.
• The API key and the LAN-share PIN are independent: the PIN guards a casual share session, the key is the durable remote credential. Either can be active; both are checked when set.
• Admin routes (/system/*, /api/settings/*) stay loopback-gated unless OMNIVOICE_SERVER_MODE=1 is set on the box; in server mode the key is the access control for those too.
• The key is compared in constant time and never logged.