You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

In this exercise you will use kubectl to fetch all of the Pods running in a cluster, and format the output to pull out the list of Containers for each.

List all Container images in all namespaces

Fetch all Pods in all namespaces using kubectl get pods --all-namespaces
Format the output to include only the list of Container image names using -o jsonpath={..image}. This will recursively parse out the image field from the returned json.
- See the jsonpath reference for further information on how to use jsonpath.
Format the output using standard tools: tr, sort, uniq
- Use tr to replace spaces with newlines
- Use sort to sort the results
- Use uniq to aggregate image counts
```
kubectl get pods --all-namespaces -o jsonpath="{..image}" |\
tr -s '[[:space:]]' '\n' |\
sort |\
uniq -c
```

The above command will recursively return all fields named image for all items returned.

As an alternative, it is possible to use the absolute path to the image field within the Pod. This ensures the correct field is retrieved even when the field name is repeated, e.g. many fields are called name within a given item:

kubectl get pods --all-namespaces -o jsonpath="{.items[*].spec.containers[*].image}"

The jsonpath is interpreted as follows:

.items[*]: for each returned value
.spec: get the spec
.containers[*]: for each container
.image: get the image

Note: When fetching a single Pod by name, for example kubectl get pod nginx, the .items[*] portion of the path should be omitted because a single Pod is returned instead of a list of items.

List Container images by Pod

The formatting can be controlled further by using the range operation to iterate over elements individually.

kubectl get pods --all-namespaces -o=jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{range .spec.containers[*]}{.image}{", "}{end}{end}' |\
sort

List Container images filtering by Pod label

To target only Pods matching a specific label, use the -l flag. The following matches only Pods with labels matching app=nginx.

kubectl get pods --all-namespaces -o=jsonpath="{..image}" -l app=nginx

List Container images filtering by Pod namespace

To target only pods in a specific namespace, use the namespace flag. The following matches only Pods in the kube-system namespace.

kubectl get pods --namespace kube-system -o jsonpath="{..image}"

List Container images using a go-template instead of jsonpath

As an alternative to jsonpath, Kubectl supports using go-templates for formatting the output:

kubectl get pods --all-namespaces -o go-template --template="{{range .items}}{{range .spec.containers}}{{.image}} {{end}}{{end}}"

What's next

Reference

Jsonpath reference guide
Go template reference guide

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