concept kubelet in category kubernetes

This is an excerpt from Manning's book Core Kubernetes MEAP V02. Login to get full access to this book.

Any Pod scheduled to a kubelet’s host is running (via a control loop that watches which Pods are scheduled to which Nodes)

The API Server is continually made aware that kubelet on a Node is healthy (via a heartbeat). In Kubernetes 1.17+, you can see how this heartbeat is maintained by looking at the kube-node-lease namespace of a running cluster.

Each of the Nodes, including the control plane in the following figure, has a kubelet installed.

Figure 10.1. Basic cluster

At a high level, kubelet is a binary that runs on every Node and is a Pod scheduler and Node agent, but only for the local Node. Kubelet monitors and maintains information about the server, it runs on, in a Node object. It updates the Node object, via calls to the API server, based on changes in the Node. Start by looking at the definition of a Node, as obtained by running kubectl get nodes -o yaml on a running cluster. The next few code blocks are snippets produced by the kubectl get nodes command. You can follow along by running kind create cluster and running the kubectl commands.