Python for the backend under the argument of "build using what you know". ReactJS for frontend development because Python for frontend work I find very antiquated.
Architecture wise I'm hosted in AWS. Data is stored in MySQL and Redis. All self hosted because I'm to cheap to pay per request pricing and the overhead is very minor when done right when rolling my own
* Storing time counters on user actions (timestamp of last time a user posted/edited X, meant to be a throttling mechanism against abuse)
* Site content caching, around 20-50kb per page, each page being user generated content
Sizes will obviously vary on traction so not sure about the final numbers.
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My last 9-to-5 employer was a very well known and my largest caching tier in Redis there was 512GB in a cluster configuration. I'm using the same server configuration and sharding logic for the indie thing, just on a smaller scale