As for why Rust for the backend piece instead of php, node js, or python based backends, it has to do with Rust being more performant, and using less memory than these other options. Since it doesn't have to run a garbage collector and is a compiled language so it does not need an extra interpreter running the code, Rust needs way less CPU power for running the same logic vs these other backend frameworks which will lead to your service being able to handle far more requests per second