How to protect NodeJS application on nginx from file upload attack?

Question

Nginx

There is a working NodeJS application accepting requests through a proxying nginx server. It is necessary to implement loading and processing of small files (5-10 mb). I would like to know the possible attacks through this mechanism. Interested in the following:
1. How can the system be brought to failure in this way?
2. How to protect yourself from such attacks and prevent the termination of both the entire server and the NodeJS application itself?
3. How are nginx and nodejs properly configured to implement secure file uploads?