Kubernetes Container Image Pull Concepts

External

• https://kubernetes.io/docs/concepts/containers/images/

Internal

• Kuberntes Pod and Container Concepts

Overview

A pod's containers pull their images from their respective repositories while the pod is in Pending phase. Technically, it is the kubelet that performs the image pulling on behalf of the pod.

Pull Policy

The pull policy is configured on a per-container basis using the imagePullPolicy tag in the pod manifest.

There are three possible values: Always, IfNotPresent and Never. This attribute is optional, and if it is not specified, it is inferred based on the image tag. The default is Always if ":latest" tag is specified, or IfNotPresent otherwise.

The pull policy can be also enforced with the AlwaysPullImages admission controller.

Private Registries

https://kubernetes.io/docs/concepts/containers/images/#using-a-private-registry

https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/

Conceptually, there could be several ways to configure private registries.