The controller manager is a set of control loops that watch the changes in the API server and ensure the cluster is in the desired state. For example, the deployment controller ensures that the whole deployment is run on the desired amount of containers. The node controller responds and evicts the pod when the nodes go down. The endpoint controller is used to create a relationship between services and pods. The service account and the token controller are used to create a default account and API access tokens.
To accommodate different development paces and release cycles from different cloud providers, from Kubernetes version 1.6, cloud provider-specific logic was moved from kube-controller-manager to the cloud controller manager (cloud-controller-manager). This was promoted to beta in version 1.11.