WebSocket connection to 'ws://localhost:5000/ws' failed: Error during WebSocket handshake: Unexpected response code: 404

[septfish]

Bug description

Why did I encounter the below problem. I don't know how to solve it. I want to use superset and celery in Windows system. Is it the flask don't support the web socket? pls tell me what should I do next?

VM20494 WebSocketClient.js:17 WebSocket connection to 'ws://localhost:5000/ws' failed: Error during WebSocket handshake: Unexpected response code: 404
vendors-node_modules…ba6aa.entry.js:3845 WebSocket connection to 'ws://localhost:5000/ws' failed: Error during WebSocket handshake: Unexpected response code: 404
VM20496 index.js:494 [webpack-dev-server]
Event {isTrusted: true, type: 'error', target: WebSocket, currentTarget: WebSocket, eventPhase: 2, …}
VM20496 index.js:486 [webpack-dev-server] Disconnected!
VM20496 index.js:486 [webpack-dev-server] Trying to reconnect...
index.js:494 [webpack-dev-server]
Event {isTrusted: true, type: 'error', target: WebSocket, currentTarget: WebSocket, eventPhase: 2, …}

Screenshots/recordings

No response

Superset version

master / latest-dev

Python version

3.9

Node version

16

Browser

Chrome

Additional context

No response

Checklist

• I have searched Superset docs and Slack and didn't find a solution to my problem.
• I have searched the GitHub issue tracker and didn't find a similar bug report.
• I have checked Superset's logs for errors and if I found a relevant Python stacktrace, I included it here as text in the "additional context" section.

[dosubot[bot]]

Hi @septfish! I'm Dosu and I’m helping the superset team.

The 404 WebSocket error happens because Flask (which Superset uses for its backend) does not natively support WebSockets, and the /ws endpoint isn't handled by Flask. Superset relies on a separate Node.js WebSocket server for async features, and this server is not running by default when you just start Flask. That's why you see the 404 error when the frontend tries to connect to ws://localhost:5000/ws—there's nothing listening on that endpoint in your current setup.

Also, your Python (3.9) and Node (16) versions are not supported with the latest Superset code. Superset now requires Python 3.10 or 3.11 and Node.js 20.x. Running unsupported versions can cause frontend/backend mismatches and asset build issues, which often result in errors like this one. The recommended fix is to use a stable Superset release (like 6.0) and upgrade your Python and Node versions to the supported ones. This should resolve the WebSocket errors and improve overall stability [source].

If you need async features (like live query updates), you must run the Node.js WebSocket server alongside Flask and configure Superset to use it. The WebSocket server runs on a different port and must be started separately. For most development and production setups, using Docker Compose is the easiest way to get all required services (Flask, Celery, Node, WebSocket, Redis, etc.) running together, even on Windows [source] [source].

In summary: Flask doesn't handle WebSockets for Superset; use supported Python/Node versions; use a stable Superset release; and if you need async features, make sure the Node.js WebSocket server is running and properly configured.

To reply, just mention @dosu.

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[septfish]

I have seen the directory superset-websocket from new version 4.1.1. which configs I should set? because I also encounter the problem when I run the command "npm run dev-server" after I specified the port "8080" in config.json.

[dosubot[bot]]

To get superset-websocket working and avoid the 404 WebSocket errors, you need to:

1. Copy config.example.json to config.json in the superset-websocket directory and set the "port" field to the port you want (e.g., 8080). Make sure Redis connection details, "jwtSecret", and "jwtCookieName" are set and match the values in your Superset Flask app config. These values must be consistent for authentication and async events to work. You can also use environment variables to override these settings if needed. See the full config options in the example file and code comments [config.json example] [config.ts].

2. In your Superset superset_config.py, set:

   GLOBAL_ASYNC_QUERIES = True
   GLOBAL_ASYNC_QUERIES_TRANSPORT = "ws"
   GLOBAL_ASYNC_QUERIES_WEBSOCKET_URL = "ws://localhost:8080/"

   Replace 8080 with whatever port you set in config.json. The hostname (localhost vs 127.0.0.1) must match how you access Superset in your browser [README].

3. Start Redis if it’s not already running.

4. In the superset-websocket directory, run npm run dev-server. This starts the WebSocket server on the port you set in config.json [package.json].

5. Make sure your Flask app and the WebSocket server are running at the same hostname (but different ports), and that the WebSocket URL in your Superset config matches.

If you still see 404 errors, double-check that the WebSocket server is running, the port matches in both configs, and that you’re not mixing up localhost and 127.0.0.1 in your browser and config. There are no known Windows-specific blockers, but make sure Node and Redis are installed and running properly.

Let me know if you need a sample config or run into a specific error!

To reply, just mention @dosu.

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[septfish]

Maybe I miss some config, it is the same error after I set the config as below. pls tell me what I should do next.

my config.js:
{
"port": 8080,
"logLevel": "info",
"logToFile": false,
"logFilename": "app.log",
"statsd": {
"host": "127.0.0.1",
"port": 8125,
"globalTags": []
},
"redis": {
"port": 6379,
"host": "127.0.0.1",
"db": 2,
"ssl": false
},
"redisStreamPrefix": "async-events-",
"jwtSecret": "82PCGN7HG/rDIUBKOmhvKjX5D+naaG85S77PiyRm+xZ5LLdETuH4J5DY",
"jwtCookieName": "async-token"
}

my superset_config.py:
GLOBAL_ASYNC_QUERIES = True
GLOBAL_ASYNC_QUERIES_TRANSPORT = "ws"
GLOBAL_ASYNC_QUERIES_WEBSOCKET_URL = "ws://localhost:8080/"
GLOBAL_ASYNC_QUERIES_REDIS_CONFIG = {
"host": "127.0.0.1",
"port": 6379,
"db": 2,
"ssl": False
}
GLOBAL_ASYNC_QUERIES_JWT_SECRET = "82PCGN7HG/rDIUBKOmhvKjX5D+naaG85S77PiyRm+xZ5LLdETuH4J5DY"
GLOBAL_ASYNC_QUERIES_JWT_COOKIE_NAME = "async-token"
GLOBAL_ASYNC_QUERIES_REDIS_STREAM_PREFIX = "async-events-"

[septfish]

This is my browser url: http://localhost:5000/superset/welcome/

The websocket server is run successfully in 8080 port:

[dosubot[bot]]

Your browser URL (http://localhost:5000/superset/welcome/) is the normal Superset home page and is not related to the WebSocket 404 error. The WebSocket connection should use the URL you set in your config (ws://localhost:8080/). If you still see errors about ws://localhost:5000/ws, it means the frontend is not picking up your updated WebSocket config.

To troubleshoot:

1. Open your browser's developer tools (Network tab, filter by "WS") and check the exact WebSocket URL the frontend is trying to connect to and the error/status code.
2. Make sure the superset-websocket server is running and listening on port 8080 (try visiting http://localhost:8080/health or check the terminal where you ran npm run dev-server).
3. Double-check that the JWT secret and cookie name are exactly the same in both your Superset config and superset-websocket config.json (no extra spaces or typos).
4. Clear your browser cache or do a hard refresh to make sure the frontend is using the latest config.
5. If the frontend is still trying to connect to ws://localhost:5000/ws, it may be using an old or default config. Make sure you restarted the Flask server after changing superset_config.py.

Also, your Python (3.9) and Node (16) versions are not supported with the latest Superset code. Superset now requires Python 3.10/3.11 and Node.js 20.x. Using unsupported versions can cause asset and config issues that lead to errors like this. Upgrading to supported versions and using a stable Superset release is strongly recommended for reliable async features and WebSocket support (reference).

Let me know what you see in the Network tab and if the WebSocket server is running on port 8080.

To reply, just mention @dosu.

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[septfish]

I try to reboot all the server, but don't solve the 404 problems. I have below two questions:
question one:
Is this issue related to the startup sequence?

question two:
Both Superset-Fronted and superset-websocket server should all be started, right?

[dosubot[bot]]

This issue is not related to the startup sequence—there’s no required order for starting Superset (Flask) and the superset-websocket server. What matters is that both are running at the same time and are properly configured to use the same host, port, JWT secret, and cookie name. If either service is down or misconfigured, you’ll get errors like 404 or failed WebSocket handshakes. So yes, both the Superset frontend (Flask server) and the superset-websocket server must be started and available for async features to work as expected. If you’re still seeing 404 errors, double-check that both services are running, configs match, and the frontend is using the correct WebSocket URL. Reference

To reply, just mention @dosu.

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[septfish]

Should I start server by "npm run dev" in superset-frontend too?

[dosubot[bot]]

You only need to run npm run dev (or npm run dev-server) in superset-frontend if you are actively developing the frontend and want hot-reloading or live asset updates. For normal use—including async/WebSocket features—it's not required, as Flask serves the built frontend assets by default. Just make sure your backend (Flask), superset-websocket server, and Redis are running and properly configured. If you do run the frontend dev server, access Superset at http://localhost:9000 instead of the Flask port.
Reference

To reply, just mention @dosu.

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[rusackas]

It seems that you're using Windows (unsupported) and the bot might be right about this:

your Python (3.9) and Node (16) versions are not supported with the latest Superset code.

I think this is best moved to a Discussion, where you can continue working on this with Dosu, but I don't think(?) there's a Superset bug here.