Node.js: How to attach to a running process and to debug the server with a console?

Question

I use \'forever\' to run my application. I want to attach to the running environment to inspect my application. So what can I do?

Answer 1

Starting from Node 6.3, node has a built-in debugger that can be triggered (even in a production app) by doing:

kill -USR1 

The node process will spit out something like this:

Debugger listening on ws://127.0.0.1:9229/f3f6f226-7dbc-4009-95fa-d516ba132fbd
For help see https://nodejs.org/en/docs/inspector

• If you can access the server from a browser, you can use chrome://inspect on http://host.domain:9229.

• If you cannot connect via a browser (e.g. the server is in a firewalled production cluster), you can activate a REPL to inspect over the command line:

  node inspect -p 
  

• If you can't access the server from a browser, but you can SSH into that server, then setup SSH port forwarding (ssh -nNTL 9229:localhost:9229 @ -i .pem) and you'll find your script under chrome://inspect after a few seconds.

Prior to this version, node-inspector was a separate tool for debugging Node processes. However, as documented on its own page, it is mostly deprecated as the now-bundled debugger is actively maintained and provides more advanced features. For more information on this change, see this thread.