Setting Composite SLOs is Hard. This Calculator Makes it Easy. Most reliability tracking focuses on one service at a time. That works fine until you realize that most user experiences rely on multiple services working together. Microservices, databases, APIs, and other components must function in sync for a seamless experience. On top of that, end-to-end user journeys often rely on services that have no synchronous APIs at all. If one piece fails, the whole experience can suffer.