We have more than 100k users and more than 400k contents(mongodump make about 1G size of directory).
Initially we use 1G memory machine, we find that 503 error always come. Then we upgrade the machine to 2G, some error still comes. We now have upgraded it to 4G.
I wonder that is there a suggested machine for our scale? Where is community.nodebb.org hosted?
Totally, we find the response speed is too slow for some pages of noddbb. We are not satisfied about it.
Take a look here.
I won't answer your question fully. I can say with about 50 users I was very quickly hitting 503 errors and I had to move to 1G of memory. I had some discussion with others in this thread: