The Kubernetes Controller is the core component responsible for the reconciliation process. Controllers are control loops that continuously watch the state of resources via the API Server. Each controller is responsible for a specific resource type (e.g., ReplicaSet, Deployment). It compares the desired state, defined in the resource's specification, with the actual current state of the cluster. If there is a discrepancy, the controller takes corrective action to drive the actual state towards the desired state. This "watch, compare, act" cycle is the essence of reconciliation in Kubernetes.

A. Kubernetes Scheduler: The scheduler's sole responsibility is to assign newly created pods to suitable nodes based on constraints and available resources. It does not watch or reconcile the state of existing resources.

B. Kubernetes Dashboard: The Dashboard is a web-based user interface for managing and observing the cluster. It is a client of the API server, not a core control plane component that performs reconciliation.

C. Kubernetes API Server: The API Server is the central hub that exposes the Kubernetes API and stores the cluster's state in etcd. Controllers watch the API Server, but it does not perform the reconciliation logic itself.

1. Kubernetes Official Documentation

"Controllers": In the "Controller pattern" section

it states

"In Kubernetes

controllers are control loops that watch the state of your cluster

then make or request changes where needed. Each controller tries to move the current cluster state closer to the desired state." This directly identifies controllers as the component that watches and reconciles state.

Source: https://kubernetes.io/docs/concepts/architecture/controller/

2. Kubernetes Official Documentation

"Kubernetes Components": The description of the kube-controller-manager explains that it runs controller processes. It notes

"Logically

each controller is a separate process

but to reduce complexity

they are all compiled into a single binary and run in a single process." This confirms that the controller entity is responsible for these loops.

Source: https://kubernetes.io/docs/concepts/overview/components/#kube-controller-manager

3. University of California

Berkeley

EECS Courseware (CS 194): Lecture slides on "Kubernetes Architecture" describe the role of controllers: "Controller: Watches for changes in desired state via API server

and tries to move current state towards desired state." This academic source corroborates the function of controllers in the reconciliation loop.

Source: CS 194-26: Cloud Computing

Lecture 10: Kubernetes Architecture

Slide 21. (e.g.

https://inst.eecs.berkeley.edu/~cs194-26/fa21/lectures/lec10-k8s-arch.pdf)