Applications that are deployed to various physical and logical environments (AWS, Heroku, Dev, Prod, Local, Test, Debug, Language, TodayDate, etc…) will need a way to dynamically adapt to their current environment. The path to a file on AWS is definitely different than a path to a file on a disconnected development box.

A note about supplying credentials in an application -

Credentials for accessing outside resources (databases, s3 buckets, deployment services, etc…) should not be included in any source file (config or hardcoded in app) that will be checked-in to a source control system.

Config File

A smart module for handling config files is necessary. You can create your own, or just use one that has already been created and tested, like nodejs-config.
npm install nodejs-config

Environment Variables

Sometimes, using environment variables is the way to go. Like when the application needs credentials data such as username and password.