When it comes to reliable web applications, one principle rules them all: idempotency. This ability to rerun a function, make a REST API call, or process a message any number of times and ensure the same result is extremely hard to do reliably. But it is possible and we should always strive to achieve it! In this talk, I’d like to explain and explore the importance of idempotency and discuss how we can implement it in our own systems, including: You’ll leave this talk with a deeper understanding and appreciation for this tongue-twisting principle and start combing through your code with an idempotent eye.