Getting custom output from kubectl with examples

Example-9: Printing data using go-template(-o go-template)

This is another powerful way to extract the data we need from the kubectl output.  You can find the official documentation here. 

kubectl get pod -o go-template='Some random string'
Some random stringfoo@host:$

#with a new line

kubectl get pod -o go-template='Some random string{{"\n"}}'
Some random string

Example-9a: Printing all the pod names in a namespace

Notice the 1st column; in the default namespace, there are 3 pods, so our go-template is iterating three times. 0,1 and 3rd time. 

kubectl get pod -o go-template='{{range $index,$pod := .items}}{{$index }} {{.metadata.name}}{{"\n"}}{{end}}'
0 pod-with-few-containers
1 simple-pod
2 web-server

Analogous:

To visualize using bash, we create an array called foo and store four strings. 

foo=('line one' 'line two' 'line three' 'line four')

Now printing the index of the element and the value:

for i in "${!foo[@]}"; do printf "%s\t%s\n" "$i" "${foo[$i]}"; done
0     line one
1     line two
2     line three
3     line four

In the same example, without an index, I could not think of any use case where we would need to print the index. 

kubectl get pod -o go-template='{{range $index,$pod := .items}}{{.metadata.name}}{{"\n"}}{{end}}'
pod-with-few-containers
simple-pod
web-server

OR, you may skip the index:

kubectl get pod -o go-template='{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}'
pod-with-few-containers
simple-pod
web-server

Example-9b: Printing the pod name and namespace(notice the spaces between the columns, they are not so nice.)

kubectl get pod -A -o go-template='{{range $index,$pod := .items}}{{.metadata.name}} {{.metadata.namespace}} {{"\n"}}{{end}}'
pod-with-few-containers default
simple-pod default
web-server default
coredns-76b4fb4578-sv42x kube-system
coredns-76b4fb4578-k567x kube-system
dns-autoscaler-79a9ssb6659-c2wfb kube-system

Example-9c: Printing the output with the desired padding in go-template

Here we use the built-in function “printf” to get the padding between the columns as per our requirements. Notice that we do not need a separate {{“\n”}} to get a new line. 

kubectl get pod -A -o go-template='{{range $index,$pod := .items}}{{printf "%-40s %20s\n" .metadata.name .metadata.namespace}}{{end}}'
pod-with-few-containers                    default
simple-pod                                 default
web-server                                 default
coredns-76b4fb4578-2v42x                   kube-system
coredns-76b4fb4578-s567x                   kube-system
dns-autoscaler-7979fb6659-c2wfb            kube-system
kube-apiserver-kube-master                 kube-system
kube-controller-manager-kube-master        kube-system
kube-proxy-55kwq                           kube-system

Example-9d: Printing the pods belonging to a particular namespace(using conditional statement -> if/else)

 In the below example, we are using conditional statements to only print the pod name, which belongs to the “default” namespace.  

kubectl get pod -A -o go-template='{{range $index, $element := .items}}{{ if (eq $element.metadata.namespace "default")}}{{$element.metadata.name}}{{"\n"}}{{ end }}{{end}}'
pod-with-few-containers
simple-pod
web-server

The syntax for conditional statements, where LHS and RHS are two values.

{{ if (eq LHS RHS) }} 
    {{ If true, do this action }}
{{else}}
    {{if false do this action}}
{{end}}

Other comparison operators are:

eq
	Returns the boolean truth of arg1 == arg2
ne
	Returns the boolean truth of arg1 != arg2
lt
	Returns the boolean truth of arg1 < arg2
le
	Returns the boolean truth of arg1 <= arg2 gt Returns the boolean truth of arg1 > arg2
ge
	Returns the boolean truth of arg1 >= arg2

Example-9e: Using the multi-line go-template

The following command is the same as the above but looks more readable.  However, you will not like the output if you run the below command. It will be full of weird newlines and spaces. This is because I am not pasting the output here. 

kubectl get pod -A -o go-template='{{range $index, $element := .items}}
                                       {{ if (eq $element.metadata.namespace "default")}}
                                           {{$element.metadata.name}}{{"\n"}}
                                       {{ end }}
                                   {{end}}'

The solution for using a multi-line go template is using “{{-” and “-}}” for stripping the leading and trailing newlines and spaces. The below output is clean even when a multi-line command is used. 

kubectl get pod -A -o go-template='{{ range $index, $element := .items }}
                                       {{- if (eq $element.metadata.namespace "default") -}}
                                           {{$element.metadata.name}}{{"\n"}}
                                       {{- end -}}
                                   {{ end }}'
pod-with-few-containers
simple-pod
web-server

Example-9f: Printing the pod name, container name, and their status

 kubectl get pod -o go-template='{{range $index, $element := .items}}
                                    {{- range $container, $status := $element.status.containerStatuses -}}
                                        {{- if not .ready -}}
                                            {{printf "%-40s %40s %30s\n" $element.metadata.name $status.name "not-ready" }}
                                        {{- else -}}
                                            {{printf "%-40s %40s %30s\n" $element.metadata.name $status.name "ready"}}
                                        {{- end -}}
                                     {{- end -}}
                                {{end}}'
pod-with-few-containers container-1 ready
pod-with-few-containers container-2 not-ready
pod-with-few-containers container-3 not-ready
simple-pod simple-pod ready
web-server container-1 ready
web-server container-2 not-ready

The above example can be further cleaned; notice that the nested loop is made over the container status.  This is one example of text formatting; there is an endless combination you can play around with. 

kubectl get pod -o go-template='{{$podname := ""}}
                                {{- range $index, $element := .items -}}
                                    {{- range $container, $status := $element.status.containerStatuses -}}
                                        {{ if (eq $container 0 )}}
                                            {{- $podname = printf "%s %s" $element.metadata.name "\n|-->" -}}
                                        {{else}}
                                            {{- $podname = "|-->" -}}
                                        {{end}}
                                         {{- if not .ready -}}
                                             {{ $podname }} {{ $status.name }} {{ "not-ready" }}{{"\n"}}
                                         {{- else -}}
                                             {{$podname}} {{ $status.name }} {{"ready"}}{{"\n"}}
                                         {{- end -}}
                                    {{- end -}}
                                {{- end -}}'
pod-with-few-containers
|--> container-1 ready
|--> container-2 not-ready
|--> container-3 not-ready
simple-pod
|--> simple-pod ready
web-server
|--> container-1 ready
|--> container-2 not-ready

Now Print the pod name, container name, and their respective images.

kubectl get pod -o go-template='{{$podname := ""}}
                                {{- range $index, $element := .items -}}
                                    {{- range $container, $status := $element.status.containerStatuses -}}
                                        {{ if (eq $container 0 )}}
                                            {{- $podname = printf "%s %s" $element.metadata.name "\n|-->" -}}
                                        {{else}}
                                            {{- $podname = "|-->" -}}
                                        {{end}}
                                        {{- if not .ready -}}
                                            {{ $podname }} {{ $status.name }} {{ "not-ready" }}{{"\n"}}
                                        {{- else -}}
                                            {{$podname}} {{ $status.name }} {{"ready"}}{{"\n"}}
                                        {{- end -}}
                                    {{- end -}}
                                {{- end -}}'
pod-with-few-containers
|--> container-1(docker.io/library/nginx:latest) ready
|--> container-2(docker.io/library/busybox:latest) not-ready
|--> container-3(docker.io/library/busybox:latest) not-ready
simple-pod
|--> simple-pod(docker.io/library/nginx:latest) ready
web-server
|--> container-1(docker.io/library/nginx:latest) ready
|--> container-2(docker.io/library/busybox:latest) not-ready

Another Variation: Perhaps simpler than the last one. 

kubectl get pod -o go-template='{{$ready :=""}}{{range .items}}{{ printf "POD:\t%-40s(%s)\n" .metadata.name (.metadata.namespace)}}{{range .status.containerStatuses}}{{ if .ready }}{{$ready = "ready"}}{{else}}{{$ready = "not-ready"}}{{end}}{{printf "\t|->%-20s %20s %20s\n" .name .image $ready}}{{end}}{{"\n"}}{{end}}'
POD: pod-with-few-containers (default)
|->container-1 docker.io/library/nginx:latest ready
|->container-2 docker.io/library/busybox:latest not-ready
|->container-3 docker.io/library/busybox:latest not-ready
POD: simple-pod (default)
|->simple-pod docker.io/library/nginx:latest ready
POD: web-server (default)
|->container-1 docker.io/library/nginx:latest ready
|->container-2 docker.io/library/busybox:latest not-ready

Be Creative!