The API backend is written in Swift with some code in C (conversion Float16, interpolations, some solar radiation libraries). Data are read directly via mmap from local NVMe SSD disks. To scale, I can add new VMs and copy my binary files.

There is no frontend cache and I want to keep it this way. Next steps include point-of-presence API virtual machines in different counties. Via GeoDNS this is even faster than a CDN.

Peak API usage was around 50.000 API calls per hour, but on average it is quite low.