Hands-on Lab·Kubernetes and Cloud Native Security Associate
Image Tags, Digests and Pull Policy
Supply chain security starts with a question with a surprising answer: what did this Pod actually run? A tag is a mutable pointer, and the cluster records what it resolved to in a different field. This guide reads both, then makes pinning compulsory with one CEL expression.
Platform Security Guide 33 of 42 Intermediate
- Kubernetesapiserver v1.36.4, kubelet v1.36.3
- Runtimecontainerd 2.2.6
- CNICilium 1.18.1 - tunnel/VXLAN, with Hubble relay and UI
- Host OSUbuntu 26.04 LTS, kernel 7.0.0-29
- Built withkubeadm v1.36.3 - podSubnet 10.244.0.0/16, serviceSubnet 10.96.0.0/12
- TimeAbout 17 min
- Reviewed25 August 2026
Written against the versions above. `imagePullPolicy` defaults from the tag: `Always` for `:latest`, `IfNotPresent` otherwise. The `AlwaysPullImages` admission plugin exists and is not enabled by default.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| CKA5001 | 192.168.0.41 | Ubuntu 26.04 LTS | Control Plane Node (tainted NoSchedule) | 2 Core | 4 GB | 50 GB |
| CKA5001-NODE01 | 192.168.0.42 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
| CKA5001-NODE02 | 192.168.0.43 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
| CKA5001-NODE03 | 192.168.0.44 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
Before you start
-
Two fields, and only one of them is what you wrote
-
The pull policy neither Pod set
-
The plugin that would close the cache hole
-
Pinning to what actually ran
-
Making it compulsory