Foreword by John A. De Goes

We live in a complex and demanding cloud-native world. The applications that we develop are small parts of a much larger, globally distributed whole.

Modern applications must process a never-ending stream of new data and requests from all over the world, interacting with hundreds or even thousands of other services remotely distributed across servers, racks, data centers, and even cloud providers.

Modern applications must run 24/7, deal with transient failures from distributed services, and respond with ultra-low latency as they process the data and requests from desktops, smartphones, watches, tablets, laptops, devices, sensors, APIs, and external services.

The complexity of satisfying these requirements gave birth to reactive programming, a style of designing applications that are responsive, resilient, elastic, and event-driven.

This is the world that created ZIO, a new library that brings the power of functional programming to deliver a powerful new approach to building modern applications.