I'm developing a social network with Django (Python) + Postgres SQL. My site will have a chat feature so that users can communicate to each other in real-time, and the communication will be only from user-to-user (so there won't be chatrooms with more than two people).
Let's say that in the future my social network has ten millions of registered users (I know, I know, but for the sake of my question let's assume that this happens) and an average of 20,000 chats open between users at the same time 24/7.
Assuming that I run my app on the Cloud (Digital Ocean, AWS or whatever) with a traffic balancer, can I expect my Django + SQL app to run seamlessly or should I use Node JS + noSQL to scale my app without so much pain as it grows?
I heard that the ME*N stack is meant for these kind of use cases (real-time applications with thousands of concurrent connections), but I already developed around 25% of my app in Django + Postgres and I get discouraged to think that I will probably have to re-do everything again from scratch. But on the other hand, I heard that some other big websites such as Instagram have been developed using Django, so I don't know what to think.
I'm aware that it's possible to connect Django with MongoDB, but I still have the problem with managing the big amount of concurrent real-time connections... Plus, I will use React heavily on the front-end and it might be easier to couple it with Node than with Django.
What is the best decision here?