§Lagom design philosophy

Consider some of the basic requirements of a Reactive Microservice as identified by Jonas Bonér (quotes extracted from Reactive Microservices Architecture: Design Principles for Distributed Systems):

• “Isolation is a prerequisite for resilience and elasticity and requires asynchronous communication between service boundaries …”
• “An autonomous service can only promise its own behaviour by publishing its protocol/API.” and “For a service to become location transparent, it needs to be addressable.”
• “What is needed is that each Microservice take sole responsibility for their own state and the persistence thereof.”

The following Lagom characteristics promote these best practices:

• Lagom is asynchronous by default — its APIs make inter-service communication via streaming a first-class concept. All Lagom APIs use the asynchronous IO capabilities of Akka Stream for asynchronous streaming; the Java API uses JDK8 CompletionStage for asynchronous computation; the Scala API uses Futures.

• Lagom favors distributed persistent patterns in contrast with traditional centralized databases. We encourage — but do not require — an event-sourced architecture for data persistence. The default pattern for persisting entities takes advantage of Event Sourcing (ES) with Command Query Responsibility Segregation (CQRS). Managing data persistence explains at a high level what event sourcing is and why it is valuable. Persistent Entity introduces Lagom’s implementation of event sourcing.

• Lagom provides an implementation of a service registry and a service gateway for development purposes along with the internal plumbing for managing client and server-side service discovery. Registering and discovering services introduces these concepts.