Testcontainers is an opensource library for providing lightweight, throwaway instances of common databases, Selenium web browsers, or anything else that can run in a Docker container.

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You can use environment variable.
For example:

1) NODE_PORT=3002 pm2 start -I 0 app.js

2) Read value in app:

console.log(process.env.NODE_PORT);

Or, if you are build express app:

1) PORT=3002 pm2 start -I 0 ./bin/www

2) Express load PORT automatically at start application.