> ## Documentation Index
> Fetch the complete documentation index at: https://cerebrium.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# WebSocket Endpoints

WebSocket endpoints stream responses to the client, enabling real-time, bidirectional communication.

## Required changes

Setting up a WebSocket endpoint requires a custom runtime. Configure it in `cerebrium.toml`:

```toml theme={null}
[cerebrium.runtime.custom]
port = 5000
entrypoint = "uvicorn main:app --host 0.0.0.0 --port 5000"
healthcheck_endpoint = "/health"
readycheck_endpoint = "/ready"
```

Fields:

* `port`: The port the app listens on inside the container.
* `entrypoint`: The command to start the app. This example uses Uvicorn to run a FastAPI app in `main.py`.
* `healthcheck_endpoint`: Confirms instance health. Defaults to a TCP ping on the configured port. A non-200 response marks the instance as *unhealthy*, triggering a restart if it does not recover.
* `readycheck_endpoint`: Confirms the instance is ready to receive traffic. Defaults to a TCP ping on the configured port. A non-200 response removes the instance from request routing.

## Things to note

* Custom Runtime Required: WebSocket endpoints require a custom runtime to control how the app runs inside the container.

* WebSocket URL: Requests must use a `wss://` URL. The client must support secure WebSocket connections.

## Making a request

Test the WebSocket endpoint using websocat, a command-line WebSocket client:

```bash theme={null}
websocat wss://api.aws.us-east-1.cerebrium.ai/v4/<your-project-id>/<your-app-name>/<your-websocket-function-name>
```

## Implementing the WebSocket Endpoint

Example WebSocket endpoint using FastAPI:

```python theme={null}
# In main.py:
from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/your-websocket-function-name")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_text("Hello, WebSocket!")
    await websocket.close()
```

## Additional Info

Client-side Implementation: Handle the WebSocket connection properly on the client, including error handling and reconnection logic.

```javascript theme={null}
// Example using JavaScript in a browser
const socket = new WebSocket(
  "wss://api.aws.us-east-1.cerebrium.ai/v4/<your-project-id>/<your-app-name>/<your-websocket-function-name>",
);

socket.onopen = function (event) {
  console.log("WebSocket is open now.");
};

socket.onmessage = function (event) {
  console.log("Received data: " + event.data);
};

socket.onclose = function (event) {
  console.log("WebSocket is closed now.");
};

socket.onerror = function (error) {
  console.error("WebSocket error observed:", error);
};
```