[memefrog]

50 million daily users is a lot. In ~2012, Reddit apparently had ~1.5m DAU. That was still a pretty decent website. Pulling random numbers out of the hat, maybe each daily active user makes 5 requests per day, on average? Many might just open up one thread, but a Pareto distribution means a small percentage would make hundreds of requests per day. So maybe more than 5? To be conservative, let's say 10.

So that's 15m requests per day. That's about 200 per second. Couldn't you do that on a single server using just PHP? Obviously these are just ballpark estimates but really.

When you say uptime similar to reddit, do you mean uptime similar to reddit now? Or similar to early reddit? Early reddit constantly threw errors at busy times.