Load Balancers, Reverse Proxies and API Gateways

Three kinds of server sit between the reader and your code, and from the outside they look alike: each receives a request and passes it on. What separates them is the job. A load balancer spreads requests across copies of one server, a reverse proxy shields a single origin and does work on its behalf, and an API gateway routes each call to one of many services and applies rules such as authentication once. You will see the load balancing algorithms run on the same six requests, learn why a health check can pass while users see errors, tell layer 4 from layer 7, and choose the front door for a given system. How rate limits are counted is left to the subject on resilient systems.