KodeKloud Notes

In this article, we wrap up our kubectl refresher with two bonus commands that may appear trivial but are exceptionally useful for understanding Kubernetes API resources.

Using the "kubectl explain" Command

The primary command is:

kubectl explain

This command serves as an inline documentation tool for Kubernetes API resources. For example, if you want to inspect detailed information about a Pod—including its API version, kind, metadata, specification, and status—you can run:

bash
controlplane ~ ➜  k explain pods
KIND:     Pod
VERSION:  v1

DESCRIPTION:
Pod is a collection of containers that can run on a host. This resource is
created by clients and scheduled onto hosts.

FIELDS:
  apiVersion <string>
    APIVersion defines the versioned schema of this representation of an object.
    Servers should convert recognized schemas to the latest internal value, and
    may reject unrecognized values. More info:
    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources

  kind <string>
    Kind is a string value representing the REST resource this object
    represents. Servers may infer this from the endpoint the client submits
    requests to. Cannot be updated. In CamelCase. More info:
    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds

  metadata <ObjectMeta>
    Standard object's metadata. More info:
    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata

  spec <PodSpec>
    Specification of the desired behavior of the pod. More info:
    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

  status <PodStatus>
    Most recently observed status of the pod. This data may not be up to date.
    Populated by the system. Read-only. More info:
    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

controlplane ~ ➜

Tip

If you're unsure about any Kubernetes resource or its fields, remember that the kubectl explain command is a quick way to access the documentation you need directly from your CLI.

Exploring Nested Fields with the Recursive Flag

To obtain even more granular details about a specific section, such as the fields under the spec field (for example, the security context), you can append .spec to the command. For nested objects, use the recursive flag to dive deeper:

controlplane ~ ➜ k explain pods.spec.securityContext --recursive
KIND:     Pod
VERSION:  v1
FIELD:    securityContext <PodSecurityContext>

DESCRIPTION:
SecurityContext holds pod-level security attributes and common container settings. Optional: Defaults to empty. See type description for default values of each field.
PodSecurityContext holds pod-level security attributes and common container settings. Some fields are also present in container.securityContext. Field values of container.securityContext take precedence over field values of PodSecurityContext.

FIELDS:
  fsGroup                             <integer>
  fsGroupChangePolicy                 <string>
  runAsGroup                          <integer>
  runAsNonRoot                        <boolean>
  runAsUser                           <integer>
  seLinuxOptions                      <SELinuxOptions>
      level                           <string>
      role                            <string>
      type                            <string>
      user                            <string>
  seccompProfile                      <SeccompProfile>
  localhostProfile                    <string>
  type                                <string> -required-
  supplementalGroups                  <integer>
  sysctls                             <[]string>
      name                            <string> -required-
      value                           <string> -required-
  windowsOptions                      <WindowsSecurityContextOptions>
  gmsaCredentialSpec                  <string>
  gmsaCredentialSpecName              <string>
  hostProcess                         <boolean>
  runAsUserName                       <string>
controlplane ~ ➜

This recursive command offers a comprehensive view of all fields within the PodSecurityContext. The same approach can be employed for Custom Resource Definitions (CRDs) and any non-native Kubernetes resources. Simply run the command against the desired CRD to retrieve complete documentation.

Additional Insight

Using the recursive flag is particularly useful when troubleshooting or configuring complex deployments, as it helps you understand the full hierarchy of nested fields.

Happy exploring!

Useful Links and References

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