State Store

The 4th pattern to build microservices is to use Lightweight Frameworks. Lightweight Frameworks provide similar functionality to Heavyweight Frameworks, but they heavily rely on: the event broker the container management system (CMS) In many cases they exceed Heavyweight Frameworks. Different apps can use any/different resources from the cluster which are better fit their needs. While still provide Scaling and Recovering from Failures (again by heavily relying on event broker and CMS).

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: