I've never heard of them being unreliable, and certainly not notoriously so. What sources do you have on this? My own impression formed from reading HN is that opinion around Redis is nearly entirely (almost cultish-ly) positive.

I'm just checking if there is something I missed.

> Because Redis' database is stored exclusively in RAM, which is an order of magnitude more expensive than even SSD.

Maybe, but still very cheap. Unless you are talking about insanely high priced cloud services.

Something like Hetzner would provide you with 128GB of ram for 60 euros / month or 1TB of ram for around 500 euros / month.

Not exactly true. There are things like "Redis on Flash" that redis.com offers for large sets of data. If you enable it, most of your data gets stored in a Flash memory and hence super cheap, in fact even cheaper than things like DynamoDB and stuff.