[noaheverett]

Can speak to the DB side of things: Redis in front of an RDBMS scaled well for me at https://glue.im/noah

Timlines/activity are built from the RDBMS and served from Redis as a cache. New posts are added to the cache directly as well so only needs to rebuild if you lose the entire cache which only happens if we need to restart the server. Also not storing full posts in Redis, just IDs, pulling via primary key from DB is very fast.

That same setup was used for a previous app that had a few million user base (don’t remember the concurrent user numbers though) and it ran well with a clear path to scale it up.

More thoughts: build a mobile friendly web app first, you’re gonna need some sort of back-end to run the iOS app anyways and tweaking a web app UI is much quicker than resubmitting iOS builds to the App Store.