doomsdaychicken

I’ve been looking at error monitoring services for my SaaS app, but there seems to be so many (Airbrake, Sentry, Rollbar, Bugsnag...) Have you had success with any of them?

I'm a newer programmer who is trying to understand web security.

Say I were to build an IP address lookup API service. I want to make sure that requests come from where they say they do. So I don't want someone to spoof example.com and make a request to my service. Is there a way to do this, without making the real example.com use server side code?

Why not just a private key? Is there any good reading or tutorials on this subject?

I have a bunch of web apps that I'd like to host without too much headache? Digitalocean is nice but I have to manually monitor each one. None of them require databases or any complex configuration.