This document is aimed at users who have worked through some of the examples, and who want to learn more about using kubectl to manage resources such as pods and services. Users who want to access the REST API directly, and developers who want to extend the Kubernetes API should refer to the api conventions and the api document.
When you create a resource such as pod, and then retrieve the created resource, a number of the fields of the resource are added. You can see this at work in the following example:
$ cat > /tmp/original.yaml <<EOF apiVersion: v1 kind: Pod metadata: name: foo spec: containers: - name: foo image: busybox restartPolicy: Never EOF $ kubectl create -f /tmp/original.yaml pods/original $ kubectl get pods/foo -o yaml > /tmp/current.yaml pods/original $ wc -l /tmp/original.yaml /tmp/current.yaml 51 /tmp/current.yaml 9 /tmp/original.yaml 60 total
The resource we posted had only 9 lines, but the one we got back had 51 lines.
diff -u /tmp/original.yaml /tmp/current.yaml, you can see the fields added to the pod.
The system adds fields in several ways:
metadata.uidis set synchronously. (Read more about metadata).
status.hostIPis set only after the pod has been scheduled. This often happens fast, but you may notice pods which do not have this set yet. This is called Late Initialization. (Read more about status and late initialization).
spec.containers.imagePullPolicyalways defaults to
IfNotPresentin api v1.
spec.containers.resources.limits.cpumay be defaulted to
100mon some clusters, to some other value on others, and not defaulted at all on others.
The API will generally not modify fields that you have set; it just sets ones which were unspecified.
You can browse auto-generated API documentation here.