Kubernetes Field Selectors

Field selectors allow you to choose Kubernetes resources based on the contents of one or more resource fields.

Here are some examples of field selector queries:

• metadata.name=my-service

• metadata.namespace!=default

• status.phase=Pending

Let's assume, you want to choose all pods that are currently running in the default namespace. To do so, use the following command:

kubectl get pods --field-selector status.phase=Running

The -n flag can be used to select all objects in a namespace, but what if you want to select all objects in the cluster except the namespace? Field selectors can assist you.

kubectl get pods --all-namespaces --field-selector metadata.namespace!=default

Chained selectors

You can also use multiple field selectors in your command if you need a highly specific selection. Below kubectl command selects all Pods for which the status.phase does not equal Running and the spec.restartPolicy field equals Always:

kubectl get pods --field-selector=status.phase!=Running,spec.restartPolicy=Always

Supported operators

You can use the =, ==, and != operators with field selectors (= and == mean the same thing). Below kubectl command selects all Kubernetes Services that aren't in the default namespace:

kubectl get services  --all-namespaces --field-selector metadata.namespace!=default

Multiple resource types

You can use field selectors across multiple resource types. The below kubectl command selects all Statefulsets and Services that are not in the default namespace:

kubectl get statefulsets,services --all-namespaces --field-selector metadata.namespace!=default

I'll end this post here to keep it brief.

Thank you for reading!

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