What is Kubernetes plugin

The Kubernetes plugin allocates Jenkins agents in Kubernetes pods. Within these pods, there is always one special container jnlp that is running the Jenkins agent. Other containers can run arbitrary processes of your choosing, and it is possible to run commands dynamically in any container in the agent pod.

Pod templates defined using the user interface declare a label. When a freestyle job or a pipeline job using node('some-label') uses a label declared by a pod template, the Kubernetes Cloud allocates a new pod to run the Jenkins agent.

It should be noted that the main reason to use the global pod template definition is to migrate a huge corpus of existing projects (including freestyle) to run on Kubernetes without changing job definitions. New users setting up new Kubernetes builds should use the podTemplate step 

The podTemplate step defines an ephemeral pod template. It is created while the pipeline execution is within the podTemplate block. It is immediately deleted afterwards. Such pod templates are not intended to be shared with other builds or projects in the Jenkins instance.

The following idiom creates a pod template with a generated unique label (available as POD_LABEL) and runs commands inside it.

podTemplate {

    node(POD_LABEL) {

        // pipeline steps...

    }

}

podTemplate {

    node(POD_LABEL) {

        stage('Run shell') {

            sh 'echo hello world'

        }

    }

}

references:

https://plugins.jenkins.io/kubernetes/