VoiceStudio/docs/remote-gpu.md

Remote GPU backend

Run the VoiceStudio 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.

Calling the API from your own scripts rather than the desktop app? See docs/api-auth.md for a consumer-focused reference of every auth gate (share PIN, API key, dictation WebSocket, trusted networks) with the exact headers, params, and 401/403/429 meanings.

Want to keep working here and only send individual jobs to another GPU? That is a different feature — see docs/remote-workers.md. This page moves the whole backend (and your projects with it) to the other machine; remote workers keep everything local and farm out single tasks. Both are supported, and setting one up does not affect the other.

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              │
│ VoiceStudio UI  │ ──────────────────────────▶ │ VoiceStudio backend    │
│ (thin client) │  short-lived session/ticket │ OMNIVOICE_API_KEY set │
└──────────────┘                              └─────────────────────┘

The desktop app is the thin client — there is no separate binary. You enter a Backend URL and an API key in Settings. The key is exchanged once for a short-lived session; ordinary HTTP requests use that session and WebSockets use path-bound, single-use tickets. The master is never stored or put in a URL.

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=….

If a browser will load the UI from a different origin than the backend (e.g. a Vite dev server on :3901 opened via the box's LAN IP), you also need the backend's CORS allow-list to include that origin — see Browsers from another origin (CORS); neither server mode nor trusted networks covers CORS.

When OMNIVOICE_API_KEY is set, every non-loopback request needs an accepted credential. Scripts should use Authorization: Bearer <key>. Legacy ?api_key= and ov_key transports remain accepted for compatibility, but the backend no longer creates a master-key cookie and the bundled UI uses only short-lived sessions. Loopback traffic on the box itself remains ungated.

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). Uvicorn trusts proxy headers from loopback by default, so Serve's forwarded HTTPS scheme becomes the authoritative ASGI scheme and browser session cookies receive Secure. For a non-loopback reverse proxy, explicitly configure Uvicorn's --forwarded-allow-ips=<proxy-ip>; the application never trusts an arbitrary X-Forwarded-Proto header itself.

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 the auth-exempt {url}/health with no credential, then exchanges the entered key for a session if health succeeds.
• Save & reload stores only the URL and restarts the UI against the remote. The key input is cleared after its single exchange. 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 fragment is scrubbed synchronously, then the key is exchanged once for an eight-hour maximum session; the master is not stored. 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 short-lived session. Cross-origin bearer sessions are tab-scoped; closing the tab requires re-entry. If a request 401s again (expired/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 first-party UI never persists OMNIVOICE_API_KEY, never creates a URL containing it, and never puts its administrator session in a WebSocket URL. WebSocket tickets expire after 30 seconds and work once for one path.
• 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 API key is the access control for those too (the short share PIN is consumption-only and does not gate admin) — see the credential rule below.
• Trust a LAN or reverse proxy with OMNIVOICE_TRUSTED_NETWORKS. If you run VoiceStudio behind a reverse proxy (nginx, Caddy, NPM) or only expose it on a trusted LAN/Tailnet, set OMNIVOICE_TRUSTED_NETWORKS to a comma-separated list of CIDRs (e.g. 192.168.1.0/24,10.0.0.0/8); clients from those networks are then treated as trusted by the consumption gates (share PIN, API key, dictation WebSocket) and need no key/PIN. Admin routes (/system/*, /api/settings/*) stay true-loopback-only — use OMNIVOICE_SERVER_MODE=1 for headless admin. It's the granular alternative to OMNIVOICE_SERVER_MODE=1 (which trusts all non-loopback sources) and sidesteps a proxy that strips the Authorization header. Default empty — no change to the strict loopback default. Trusted-network membership is a consumption exemption only — it never unlocks admin by itself, even in server mode (#1213). When combined with OMNIVOICE_SERVER_MODE=1, a trusted-network client that presents no credential still gets 403 on the admin routes (unless no credential is configured at all, the bare-Docker #261 flow, where admin is open); if a credential is set, only the API key — not the share PIN — reaches admin. See api-auth.md for the full two-tier model.
• The key is compared in constant time and never logged.