Skip to main content
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: 
[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: 
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: 
# 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. 
// 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);
};