Kubernetes: Up and Running, 2nd Edition

Chapter 16. Extending Kubernetes

From the beginning, it was clear that Kubernetes was going to be more than its core set of APIs; once an application is orchestrated within the cluster, there are countless other useful tools and utilities that can be represented and deployed as API objects in the Kubernetes cluster. The challenge was how to embrace this explosion of objects and use cases without having an API that sprawled without bound.

To resolve this tension between extended use cases and API sprawl, significant effort was put into making the Kubernetes API extensible. This extensibility meant that cluster operators could customize their clusters with the additional components that suited their needs. This extensibility enables people to augment their clusters themselves, consume community-developed cluster add-ons, and even develop extensions that are bundled and sold in an ecosystem of cluster plug-ins. Extensibility has also given rise to whole new patterns of managing systems, such as the operator pattern.

Regardless of whether you are building your own extensions or consuming operators from the ecosystem, understanding how the Kubernetes API server is extended and how extensions can be built and delivered is a key component to unlocking the complete power of Kubernetes and its ecosystem. As more and more advanced tools and platforms are built on top of Kubernetes using these extensibility mechanisms, a working knowledge of how they operate is critical to understanding ...