# Vercel

> Run WebSocket voice sessions on Vercel Functions with the Bun runtime, and what Vercel can't host.

Source: https://polvallverdu.github.io/pipedog/docs/deployment/vercel/



Vercel Functions can run a `server.ts` with the Bun runtime. With it, a function accepts WebSocket
upgrades and runs one voice session per socket. The code is the
[Vercel framework page](https://polvallverdu.github.io/pipedog/docs/frameworks/vercel.md), tested in
[`examples/framework-snippets/vercel`](https://github.com/polvallverdu/pipedog/tree/main/examples/framework-snippets/vercel).

Set the runtime in `vercel.json`:

```json title="vercel.json"
{ "bunVersion": "1.x" }
```

## What works [#what-works]

* **WebSocket sessions.** The `/ws` endpoint upgrades in `fetch` and runs the agent on the socket,
  with protobuf audio frames.
* **WebRTC signalling.** The `/api/offer` route answers the SDP offer, but the media can't follow:
  see below.

## Limits [#limits]

* **No WebRTC media.** SmallWebRTC needs UDP, which Vercel Functions don't carry. Use the
  WebSocket transport, or run SmallWebRTC on a [server](https://polvallverdu.github.io/pipedog/docs/deployment/servers.md).
* **One instance per socket.** Each WebSocket is pinned to one function instance for its lifetime,
  and messages don't cross instances. Keep shared state in a database.
* **Duration.** A function's maximum duration also ends a long session. Check your plan's limit
  against your longest calls.
* **Vercel Daemons** are always-on workers with no inbound HTTP or TCP traffic, so they can't serve
  these endpoints. They suit background workers that pull their own work.
* **Next.js on Vercel.** A Next.js route handler can answer the offer, but it can't upgrade a
  WebSocket. See [Next.js](https://polvallverdu.github.io/pipedog/docs/frameworks/nextjs.md).