Worker Node Components: Node Agent - kubelet

The kubelet is an agent running on each node, control plane and workers, and communicates with the control plane.
It receives Pod definitions, primarily from the API Server, and interacts with the container runtime on the node to run containers associated with the Pod.
It also monitors the health and resources of Pods running containers.

The kubelet connects to container runtimes through a plugin based interface - the Container Runtime Interface (CRI). 
The CRI consists of protocol buffers, gRPC API, libraries, and additional specifications and tools. 
In order to connect to interchangeable container runtimes, kubelet uses a CRI shim, an application which provides a clear abstraction layer between kubelet and the container runtime. 

<img src="https://github.com/sivasankarp/Kubernetes/blob/main/Container_Runtime_Interface.png"/>