In modejs, multiple express application instances are started with pm2, and the session cannot be maintained.

  node.js, question

In modejs, multiple express application instances are started with pm2, and the session cannot be maintained.
If only one example is started, but the stability of the service cannot be guaranteed, it is very difficult. Who can help to provide some ideas? Thank you very much.

Does your session exist in mongo, memory, or redis?