Reliability basics

While implementing new applications, services, or features, engineers often focus first on meeting various system requirements, such as implementing specific application features. The initial result of such work is usually some working code that correctly performs its job, such as handling some data processing task or serving network requests as an API endpoint. We can say that such code initially performs well in isolation—the implemented code produces expected outputs for the inputs we provide.

Things usually get more complex when we add more components to the system. Let’s take our movie service from Chapter 2 and assume that its API gets used by some external service that has millions of users. Our service can be implemented perfectly fine and produce the right results for various test inputs. Still, once we get requests from an external service, we may notice various issues. One of them is called denial of service (DoS)—an external service...