Every application on Cloudnode runs in a virtual machine with its own disk storage. The disk holds a full checkout of the application’s Git repository. So you have access to modules, sub-modules and static resources, you have checked in. The disk also holds all Node modules you have installed using the npm command or through dependencies in the application’s package.json descriptor. The VM contains also a minimum set of directories to get Linux running like /etc.
You should not assume, that there is write access to the disk except to the /mnt and /tmp directories. Your application can use these directories to store dynamic data. As the names suggest, /tmp can be used to store volatile files and /mnt can be used to store permanent files. These will always “follow” your application and will be mounted at /mnt.