Websockets with multiple workers #8684

seizoux · 2021-11-22T09:55:02Z

seizoux
Nov 22, 2021

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Example Code

from typing import List

from fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.responses import HTMLResponse

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>WebSocket Chat</h1>
        <h2>Your ID: <span id="ws-id"></span></h2>
        <form action="" onsubmit="sendMessage(event)">
            <input type="text" id="messageText" autocomplete="off"/>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
            var client_id = Date.now()
            document.querySelector("#ws-id").textContent = client_id;
            var ws = new WebSocket(`ws://localhost:8000/ws/${client_id}`);
            ws.onmessage = function(event) {
                var messages = document.getElementById('messages')
                var message = document.createElement('li')
                var content = document.createTextNode(event.data)
                message.appendChild(content)
                messages.appendChild(message)
            };
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


class ConnectionManager:
    def __init__(self):
        self.active_connections: List[WebSocket] = []

    async def connect(self, websocket: WebSocket):
        await websocket.accept()
        self.active_connections.append(websocket)

    def disconnect(self, websocket: WebSocket):
        self.active_connections.remove(websocket)

    async def send_personal_message(self, message: str, websocket: WebSocket):
        await websocket.send_text(message)

    async def broadcast(self, message: str):
        for connection in self.active_connections:
            await connection.send_text(message)


manager = ConnectionManager()


@app.get("/")
async def get():
    return HTMLResponse(html)


@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):
    await manager.connect(websocket)
    try:
        while True:
            data = await websocket.receive_text()
            await manager.send_personal_message(f"You wrote: {data}", websocket)
            await manager.broadcast(f"Client #{client_id} says: {data}")
    except WebSocketDisconnect:
        manager.disconnect(websocket)
        await manager.broadcast(f"Client #{client_id} left the chat")

Description

I'm using the example from FastAPI documentation for websockets, everything works fine while i have only 1 worker on my app, but when i set back 4 workers, seems that each worker has his own app instance.

How can i manage websockets within multiple workers? Each time i save a connection on the Manager class, it seems to be saved only in one random app instance, no way to save it for each app instance for each worker?

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.68.1

Python Version

3.9.4

Additional Context

No response

TheoBabilon · 2021-11-22T21:20:25Z

TheoBabilon
Nov 22, 2021

You would have to find a way to communicate events between your workers - you might want to have a look at https://github.com/encode/broadcaster
It's mentioned in the docs @ https://fastapi.tiangolo.com/advanced/websockets/ :
"But have in mind that, as everything is handled in memory, in a single list, it will only work while the process is running, and will only work with a single process.

If you need something easy to integrate with FastAPI but that is more robust, supported by Redis, PostgreSQL or others, check encode/broadcaster."

0 replies

TheJedinator · 2021-11-25T14:19:22Z

TheJedinator
Nov 25, 2021

I have successfully implemented a FastAPI server with multiple workers and web sockets using Async socketio with redis for sharing between processes. https://pypi.org/project/fastapi-socketio/

If I remember correctly I had to tweak the library to allow for async but I can't remember exactly what I had to do. Sorry.

Hope this is helpful.

0 replies

seizoux · 2024-02-13T10:17:04Z

seizoux
Feb 13, 2024
Author

I have successfully implemented a FastAPI server with multiple workers and web sockets using Async socketio with redis for sharing between processes. https://pypi.org/project/fastapi-socketio/

If I remember correctly I had to tweak the library to allow for async but I can't remember exactly what I had to do. Sorry.

Hope this is helpful.

back to topic, has anyone ever found a solution to this? it's been almost 3 years and i still didn't manage to achieve this.

2 replies

erik1110 Mar 7, 2024

I have the same question, too

YuriiMotov Mar 11, 2024

This is the answer: #8684 (comment)

lcsvcn · 2024-03-20T14:46:05Z

lcsvcn
Mar 20, 2024

no example on how to implement multiple workers with websocket?

0 replies

inventionlabsSydney · 2024-04-10T23:35:53Z

inventionlabsSydney
Apr 10, 2024

This is a very good write up on how to implement similar with Websockets and Redis Pub/Sub capabilities to allow horizontal scaling of application and worker servers.
https://medium.com/@nandagopal05/scaling-websockets-with-pub-sub-using-python-redis-fastapi-b16392ffe291

0 replies

PREPONDERANCE · 2024-04-20T12:13:50Z

PREPONDERANCE
Apr 20, 2024

I just ran into this problem where I created a web socket manager class responsible for handling all the web sockets with unique identifier.
It works fine locally but keeps telling me key error when moving it to the server.

0 replies

febin-micheal · 2024-05-01T13:44:03Z

febin-micheal
May 1, 2024

https://medium.com/@philipokiokio/broadcasting-websockets-messages-across-instances-and-workers-with-fastapi-9a66d42cb30a

0 replies

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Websockets with multiple workers #8684

First Check

Commit to Help

Example Code

Description

Operating System

Operating System Details

FastAPI Version

Python Version

Additional Context

Replies: 7 comments · 2 replies

seizoux Feb 13, 2024 Author

Replies: 7 comments 2 replies

seizoux
Feb 13, 2024
Author