A stateless system maintains no state of what happened in the past and performs its capabilities purely based on the inputs we provide to it.

Examples

A contrived stateless system receives a set of numbers as input, calculates their maximum, and returns it as a result. These inputs are either direct or indirect. Direct inputs are inputs that are included in the request, while indirect inputs are inputs that are potentially received from other systems to fulfill the request.

Imagine a service that calculates the price of a specific product by retrieving its initial price and any currently available discounts from some other services, and then performing the necessary calculations with this data. This service is still stateless.