Modularization and out-of-tree plugins

Kubernetes has made great strides toward modularization since the first edition. Kubernetes was always a paragon of flexibility and extensibility. However, originally you had to build and link your code into the Kubernetes API server or the Kublet (with the exception of CNI plugins). You also had to get your code vetted and integrated with the main Kubernetes codebase to make it available to other developers. At the time, I was very excited about Go 1.8 dynamic plugins and how they could be used to extend Kubernetes in a much more agile way. The Kubernetes developers and community took a different path and decided to make Kubernetes proper a general-purpose and versatile engine where almost every aspect can be customized or extended from the outside through standard interfaces. You've seen many examples in Chapter 17, Customizing Kubernetes - APIs and Plugins. The out-of-tree approach means that you integrate a plugin or extension with Kubernetes that...