The main lichess engine (lila, open source) is a single monolith program that's deployed on a single server. It serves ~5 million games per day. But there are a several other pieces too. They discuss the architecture here https://www.youtube.com/watch?v=crKNBSpO2_I
Easy: If something is wrong with the physical gear it's OVH's problem rather than theirs. It also means no one has to ever go to the data center which is probably important for a geographically distributed team (I assume they are). Cheap, no-frills cloud is extremely underrated, IMO.
To me those numbers seem on the high side as I'm (personally) used to (for cheap projects) scavenging together stuff from Ebay before deploying to a data centre. ;)
its also crazy how much cheaper it is than AWS. the primary DB is around $500/month with 32 CPU and 256 GB of RAM and 7TB. AWS RDS db.m6gd.8xlarge which is 32 CPU and 128 GB of RAM costs $2150/month before paying for storage as well.
Yeah, but you get what you pay for. That m6gd.8xlarge would never be subject to such a long network outage as once the hardware fault was detected, it would be moved to another machine
You have to pay 2x for multi-AZ or you get downtime for upgrades. And DB major version upgrades require manual effort unless you want to roll the dice on their new blue-green feature, which can take hours to fail or finish cutting over.
BTW consider donating if you use lichess.