Event-driven architectures enable nicely decoupled microservices and are fundamental for decentralized data management. However, using peer-to-peer event chains to implement complex end-to-end logic crossing service boundaries can accidentally increase coupling. Extracting such business logic into dedicated services reduces coupling and allows to keep sight of larger-scale flows - without violating bounded contexts, harming service autonomy or introducing god services. Service boundaries get clearer and service APIs get smarter by focusing on their potentially long running nature. I will demonstrate how the new generation of lightweight and highly-scalable state machines ease the implementation of long running services. Based on my real-life experiences, I will share how to handle complex logic and flows which require proper reactions on failures, timeouts and compensating actions and I provide guidance backed by code examples to illustrate alternative approaches.

Integrating microservices and taming distributed systems is hard. In this talk I will present three challenges we observed in real-life projects and discuss how to avoid them.

1. Communication is complex. With everything being distributed failures are normal so you need sophisticated failure handling strategies (e.g. stateful retry).

2. Asynchronicity requires you to handle timeouts. This is not only about milliseconds, systems get much more resilient when you can wait for minutes, hours or even longer.

3. Distributed transactions cannot simply be delegated to protocols like XA. So you need to solve the requirement to retain consistency in case of failures.

I will not only use slides but demonstrate concrete source code examples available on GitHub.