Which component of Kubernetes is responsible for managing the cluster's state?

The Controller Manager is the component in Kubernetes responsible for managing the desired state of the cluster. It runs controllers that watch the state of the cluster, make decisions to ensure that the current state matches the desired state, and take action to bring about any necessary changes. For instance, if a node goes down, the controllers will work to ensure that the necessary pods are rescheduled to maintain the desired number of replicas.

The Controller Manager helps to enforce resource limits, regulate replication, manage endpoint slices, and perform various housekeeping tasks that contribute to the cluster's stability and ensure continuous operation in the intended state. This function is crucial for maintaining the overall health and performance of the Kubernetes environment.

In contrast, the Kubelet primarily operates on individual nodes, ensuring that containers are running as expected, while the Scheduler focuses on resource allocation and assigning pods to specific nodes based on resource requirements and availability. The API Server serves as the frontend for the Kubernetes control plane, handling requests from clients and providing a communication path to various components of the cluster, but it does not directly manage the cluster's state.