Understanding Kubernetes Operators
Automation is at the core of the Kubernetes platform. As covered in Chapter 1, Understanding Kubernetes and Helm, Kubernetes resources can be managed either implicitly by running kubectl commands or declaratively by applying YAML-formatted representations. Once the resources are applied using the Kubernetes Command-Line Interface (CLI), one of the fundamental principles of Kubernetes is to match the current state of resources within the cluster to the desired state, a process known as the control loop. This ongoing, non-terminating pattern of monitoring the state of the cluster is implemented through the use of controllers. Kubernetes includes numerous controllers that are native to the platform, with examples ranging from admission controllers that intercept requests to the Kubernetes Application Programming Interface (API) to replication controllers that manage the number of Pod replicas that are running.
As interest in Kubernetes began to grow...