Web application firewall
Even with the safest handling of data, our application can still be vulnerable to attack. When you're exposing HTTP endpoints to the world, this is always a risk. You will be hoping for callers to behave as intended, with each HTTP conversation following a scenario that you have programmed in the service.
A client can send legitimate requests and just hammer your service with it, leading to a Denial of Service (DoS) due to all the resources then being used to handle requests from the attacker. When many hundreds or thousands of clients are used to do this, it's known as a Distributed Denial of Service (DDoS) attack. This problem sometimes occurs within distributed systems when clients have replay features that are automatically recalling the same API. If nothing is done on the client side to throttle calls, you might end up with a service overloaded by legitimate clients.
Adding protection on the server side to make such zealous clients back...