Kubelet

As explained in Kubernetes for Developers

The kubelet is a Kubernetes node agent that communicates with the control plane and manages container lifecycle on its node.

When Kubernetes runs a container on a node, the control plane decides what should run, but the node must carry out that work. The kubelet is the node-level process that communicates with the control plane and manages the lifecycle of containers through the container runtime. section 3.1.1

The kubelet operates alongside the operating system and container runtime. It starts and stops containers as requested and can take local action without waiting for the control plane. section 3.1.1

Separate kubelet responsibilities from scheduler responsibilities:

• Restarts a container when a liveness or readiness failure requires a local Pod restart. section 5.1
• Runs the containers assigned to its node and manages their lifecycle. section 3.1.1
• Does not reallocate Pods after a node disappears; the scheduler detects the node problem and places a replacement Pod elsewhere. section 5.1

A failed container

If a container fails a liveness or readiness check, the kubelet handles the restart locally. If the entire node fails, the control plane and scheduler arrange for a new Pod on a healthy node. section 5.1

Figure 3.1 Processes running on a VM, which Kubernetes calls a node

Use the node-process diagram to locate the kubelet beside the operating system and container runtime. section 3.1.1

How Kubernetes for Developers covers it

How deep it goes

Distinguishes local restarts from scheduler-driven Pod reallocation but does not detail kubelet internals.

Examples

Uses crashed-container restarts, liveness and readiness failures, and node failures that trigger Pod reallocation.

What you can do after

Understand which failures the kubelet handles locally and which failures the scheduler handles by reallocating Pods.

How it connects

Connects container lifecycle management with nodes, Pods, the control plane, scheduler, and container runtime.

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Also explained in

• 

  liveBookmanning.com
  Acing the Certified Kubernetes Administrator Exam, Second EditionThe kubelet binary is the executable program that runs the Kubernetes node agent.
• 

  liveBookmanning.com
  Kubernetes in Action, Second EditionThe kubelet is the agent on a Kubernetes node that manages the applications assigned to that node and reports their status.

Compare how 3 books explain kubelet →

Related concepts

• kubernetes api serveruses · The Kubernetes API server is the control-plane component that exposes, validates, and processes the Kubernetes API for managing cluster resources and state.
• poduses · A Kubernetes Pod is the smallest deployable unit in Kubernetes, grouping one or more co-located containers that share networking and other resources.
• Container Runtime Interfaceuses · The Container Runtime Interface is a Kubernetes standard interface through which kubelets communicate with and manage container runtimes.
• Kubernetes worker nodepart of · A Kubernetes worker node is a physical or virtual machine in a cluster that provides compute resources and runs scheduled Pods and node-level services.
• workerequivalent to · A worker is a person or computational execution unit assigned to perform a task as part of a larger system or activity.
• background processingkind of · Background processing is the execution of work independently of the immediate interactive or request-handling flow, so foreground activity need not wait for its completion.

This explainer was generated by Manning's knowledge graph from the text of Kubernetes for Developers. The section links point to the parts of the book it draws on.