Cannot start node inspector: "address already in use"

Bug report

After upgrading from Next 9.2.2 -> 9.3.0 the node inspector fails to start (crashing the Next process) with the error “Starting inspector on 0.0.0.0:9229 failed: address already in use”.

None of the suggestions offered in https://github.com/zeit/next.js/issues/10610 or https://github.com/zeit/next.js/issues/9027 have helped. Have also tested with Next 9.3.1-canary.3 and noted the same issue occurs.

To Reproduce

Steps to reproduce the behavior:

1. Run npx create-next-app
2. Add "dev": "NODE_OPTIONS='--inspect' next" to scripts
3. Run npm run dev
4. See error

Expected behavior

The node inspector starts normally without crashing the Next process.

System information

• OS: macOS 10.15.3
• Version of Next.js: 9.3.0+

[vvo]

Just updated the PR for that to solve it.

[vvo]

Update: I found the issue. When running next dev, the file next-dev-server.ts will launch a subprocess using jest-worker here: https://github.com/zeit/next.js/blob/6997b0236b68fd7c8f5395003c99a719974cc404/packages/next/server/next-dev-server.ts#L83-L91

As a result, another Node.js process is spawned with the same process.env.NODE_OPTIONS=‘–inspect’ and will also try to start a debugger on the same port than the one the main next dev command started just earlier.

This is a known issue from Node.js but there’s not much that they will do about it for good reasons, see https://github.com/nodejs/node/issues/9435#issue-186998002

But we can do something, I tried it and it works, just remove any --inspect flag from NODE_OPTIONS passed to the worker and done, see the PR: #11041