Almost every Kubernetes object includes two nested object fields that govern the object's configuration: the object spec and the object status. The spec object describes the intended state of the resource, and the status object describes the current state. You specify the spec section of the resource when you create the object. Kubernetes controllers continuously update the status of the object throughout the existence of the object. The Kubernetes control plane continuously and actively manages every object's actual state to match the desired state you supplied.

The status field uses a collection of condition resource objects with the following fields.

For example, in Kubernetes, a Deployment object can represent an application that is running on your cluster. When you create a Deployment object, you might configure the deployment spec object to specify that you want three replicas of the application to be running. Kubernetes reads the deployment spec object and starts three instances of your chosen application, and updates the status field to match your spec object. If any of those instances fails, then Kubernetes responds to the difference between the spec and status objects by making a correction, in this case to start a replacement instance.

Other common fields provide base information in addition to the spec and status fields of a Kubernetes object.

Resources in Kubernetes consist of multiple objects. These objects define the intended state of a resource. When you create or modify an object, you make a persistent record of the intended state. Kubernetes reads the object and modifies the current state accordingly.

All RHOCP and Kubernetes objects can be represented as a JSON or YAML structure. Consider the following pod object in the YAML format:

apiVersion: v1 
kind: Pod  
metadata: 
  name: wildfly  
  namespace: my_app 
  labels:
    name: wildfly  
spec: 
  containers:
    - resources:
        limits:
          cpu: 0.5
      image: quay.io/example/todojee:v1  
      name: wildfly 
      ports:
        - containerPort: 8080  
          name: wildfly
      env:  
        - name: MYSQL_DATABASE
          value: items
        - name: MYSQL_USER
          value: user1
        - name: MYSQL_PASSWORD
          value: mypa55
...object omitted...
status: 
  conditions:
  - lastProbeTime: null
    lastTransitionTime: "2023-08-19T12:59:22Z"
    status: "True"
    type: PodScheduled

Labels are key-value pairs that you define in the .metadata.labels object path, for example:

kind: Pod
apiVersion: v1
metadata:
  name: example-pod
  labels:
    app: example-pod
    group: developers
...object omitted...

The preceding example contains the app=example-pod and group=developers labels. Developers often use labels to target a set of objects by using the -l or the --selector option. For example, the following oc get command lists pods that contain the group=developers label:

[user@host ~]$ oc get pod --selector group=developers
NAME                          READY   STATUS    RESTARTS   AGE
example-pod-6c9f758574-7fhg   1/1     Running   5          11d

The -o yaml option provides a YAML-formatted output that is parsable and still human-readable.

[user@host ~]$ oc get pods -o yaml
apiVersion: v1
items:
- apiVersion: v1
  kind: Pod
  metadata:
    annotations:
...object omitted...

You can use any tool that can process YAML documents to filter the YAML output for your chosen field. For example, you can use the yq tool at https://mikefarah.gitbook.io/yq/ to process YAML and JSON files.

The yq processor uses a dot notation to separate field names in a query. The following example pipes the YAML output to the yq command to parse the podIP field.

[user@host ~]$ oc get pods -o yaml | yq r - 'items[0].status.podIP'
10.8.0.60

The [0] in the example specifies the first index in the items array.

Kubernetes uses the JSON format internally to process resource objects. Use the -o json option to view a resource in the JSON format.

[user@host ~]$ oc get pods -o json
{
    "apiVersion": "v1",
    "items": [
        {
            "apiVersion": "v1",
            "kind": "Pod",
            "metadata": {
                "annotations": {

You can use other tools to process JSON documents, such as the jq tool at https://jqlang.github.io/jq/. Similar to the yq processor, use the jq processor and dot notation on the fields to query specific information from the JSON-formatted output.

[user@host ~]$ oc get pods -o json | jq '.items[0].status.podIP'
"10.8.0.60"

Alternatively, the example might have used .items[].status.podIP for the query string. The empty brackets instruct the jq tool to query all items.

Kubernetes provides a custom output format that combines the convenience of extracting data via jq styled queries with a tabular output format. Use the -o custom-columns option with comma-separated <column name> : <jq query string> pairs.

[user@host ~]$ oc get pods \
-o custom-columns=PodName:".metadata.name",\
ContainerName:"spec.containers[].name",\
Phase:"status.phase",\
IP:"status.podIP",\
Ports:"spec.containers[].ports[].containerPort"
PodName                  ContainerName   Phase     IP          Ports
myapp-77fb5cd997-xplhz   myapp           Running   10.8.0.60   <none>

Kubernetes also supports the use of JSONPath expressions. JSONPath is a query language for JSON. JSONPath expressions refer to a JSON data structure; they filter and extract formatted fields from JSON objects.

In the following example, the JSONPath expression uses the range operator to iterate over the list of pods to extract the name of the pod, its IP address, and the assigned ports.

[user@host ~]$ oc get pods  \
-o jsonpath='{range .items[]}{"Pod Name: "}{.metadata.name}
{"IP: "}{.status.podIP}
{"Ports: "}{.spec.containers[].ports[].containerPort}{"\n"}{end}'
Pod Name: myapp-77fb5cd997-xplhz
IP: 10.8.0.60
Ports:

You can customize the format of the output with Go templates, which the Go programming language uses. Use the -o go-template option followed by a Go template, where Go expressions are inside double braces, {{ }}.

[user@host ~]$ oc get pods  \
-o go-template='{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}'
myapp-77fb5cd997-xplhz