External State Store

How to integrate event-driven microservices with request-response APIs? There are two types of external events: Autonomously Generated Events (analytical events) Reactively Generated Events (events from request-reply) There are two approaches of processing and serving requests using stateful services: using internal state stores (with silly or with smart routing) using external state stores (with regular or with composite microservice) Ways of handling requests within an event-driven workflow:

Event-Driven Microservices need to materialize states. And it comes with the important things to think about. Two approaches to choose from: Internal state store or External state store Both have pros and cons. Both have important scalability and recovery considerations. Two approaches for changing data structures: Bebuilding and Migration Transactions and how to emulate them in order to implement Effectively Once processing. All of these is disclosed in the Chapter 7 of the book we are currently studying: