THe second of the "SOLID" principles: "Software Entities should be open for extension but closed for modification"

HTTP is the heartbeat of the Web, and the key protocol through with both applications and services communicate. A general understanding of it is a key part of a developers knowledge base.

A short introduction to the nature and structure of APIs on the web.

An Application Programmer Interface is the published set of http endpoints and messages that a service can support. API design and implementation is a rich field of study - here we take a general overview.

Javalin is a lightweight framework for composing REST APIs in Java.

Evolve a simple Rest service from the existing pacemaker-skeleton app using the Javalin microframework.