Sentry.init() prevents http.Server 'upgrade' events (WebSocket) from firing

[ReneGreen27]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/node - express

SDK Version

@sentry/node: 10.47.0

Framework Version

No response

Link to Sentry event

No response

Reproduction Example/SDK Setup

Create an Express app and attach it to a shared HTTP server:

const app = express();
const server = http.createServer(app);

Attach a WebSocket upgrade handler using ws with noServer: true:

const wss = new WebSocketServer({ noServer: true });

server.prependListener('upgrade', (req, socket, head) => {
  wss.handleUpgrade(req, socket, head, (ws) => {
    // connection established
  });
});

Initialize Sentry early (either via import side-effect or preload):

import * as Sentry from "@sentry/node";

Sentry.init({
  dsn: process.env.SENTRY_DSN,
  tracesSampleRate: 1.0,
});

Start the server and attempt a WebSocket connection.

Results in

• The 'upgrade' handler is never called
• WebSocket connection fails silently
• No errors are thrown

Control (Working Case)

• Remove Sentry.init() (keep import only)
• Restart server
• WebSocket upgrade handler fires as expected

Steps to Reproduce

See above

Expected Result

Calling Sentry.init() should not interfere with Node.js HTTP server event propagation.

Specifically, handlers registered via:

server.on('upgrade', handler)
server.prependListener('upgrade', handler)

should continue to fire normally for WebSocket upgrade requests.

Actual Result

When Sentry.init() is called:

'upgrade' event listeners are never invoked
WebSocket connections fail silently
No errors are thrown
Behavior is consistent across all tested configurations

Additional Context

What Was Tried:

• Early Sentry.init() with default integrations
• Early Sentry.init() with integrations: [] and tracing disabled
• Filtering HTTP traffic using ignoreIncomingRequests for WebSocket paths
• Removing HttpServer integration explicitly
• Using server.on('upgrade') vs server.prependListener('upgrade')
• Using node --require @sentry/node/preload to force earliest initialization
• Verifying behavior with only a bare @sentry/node import (no init)
• Deferring Sentry.init() until after server + upgrade handler setup

Outcome Summary

All early initialization approaches -> 'upgrade' events do not fire
Bare import without Sentry.init() -> works
Deferred Sentry.init() -> works

Related to internal ticket #179168

Priority

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[linear-code]

JS-2054

[andreiborza]

Hi @ReneGreen27, thanks for filing.

I tried to reproduce this but don't run into the issue. What node version are you using? Could you please provide a reproduction repo that showcases the issue?