kubecontrollermanager

The kube-controller-manager is a core component of the Kubernetes control plane. It runs a set of controllers that continuously work to reconcile the actual state of the cluster with the desired state stored in the Kubernetes API server. Along with the kube-apiserver and the etcd data store, it helps maintain the overall health and behavior of the cluster by performing routine control tasks.

The controller-manager operates as a single binary, kube-controller-manager, and is typically started on each control-plane node as part of a high-availability setup. In most deployments, multiple instances may run simultaneously, but only one instance acts as the leader at a time to avoid conflicting actions. The controllers themselves watch resources via the API server, compute actions needed to reach the desired state, and then issue API requests to enact those changes.

The package provides a collection of controllers that handle different aspects of cluster operation. Examples include controllers for node lifecycle management, namespace management, service accounts and token provisioning, endpoints for services, and the service controller that maintains service-related state. It also includes workload-oriented controllers such as those for replication, jobs, daemon sets, and stateful sets, as well as a garbage collection controller to clean up unused resources. Through these controllers, the kube-controller-manager helps automate common maintenance tasks, scale workloads, and ensure resources are created, updated, or removed as required.

Overall, kube-controller-manager is essential for autonomous cluster maintenance, enabling Kubernetes to enforce desired-state configurations without manual intervention. It operates in concert with kube-scheduler and the API server to manage the lifecycle of objects in the cluster.