TL;DR about spherical harmonics: It is what you use instead of Fourier transforms if what you transform is on the surface of a sphere.

My experience is from cosmology (CMB) where they are heavily used just like Fourier transforms, I think they are also used in meteorology.

A few infrastructure things:

- Serve traffic behind a load balancer that has a WAF

- Network segregation for database (separate subnets)

- Make sure you serve https and have a cert that’s valid. Redirect to https if http

- Restrict ports on LB

At some point later:

- Endpoint monitoring and threat detection

- VPC flow logging

- Execute backend as non root

- Dependency / artifact scanning

- Cloud SIEM to monitor common actions taken

- Make sure no hard coded creds. Ie, use role-base auth with cloud providers

- Reproducible infrastructure builds with infra as code

- Email domain protection

- Grab misspellings of domain names to prevent squatting