[FIXED] Complex templating in groovy

Issue

I would like to do some templating that I would be able to do with Jinja2 or the Helm templating language inside a Jenkins shared library.

Essentially I want to dynamically render a pod definition (to be used as the kubernetets agent) like so:

renderPod() {
    return '''
apiVersion: v1
kind: Pod
metadata:
  labels:
    type: ephemeral-jenkins-agent
    pipeline: generic_pipeline
spec:
  containers:
  - name: alpine
    image: alpine:3.12.3
    command:
    - cat
    tty: true
<% if dockerBuild() %>
  - name: docker
    image: docker:18.05-dind
    securityContext:
      privileged: true
    volumeMounts:
    - name: dind-storage
      mountPath: /var/lib/docker
<% end %>
<% if dockerBuild() %>
  volumes:
    - name: dind-storage
      emptyDir: {}
<% else %>
  volumes: {}
<% end %>
    '''
}

I currently have some spaghetti code 🍝 to do this with string concatenation in a functional way, but it'd be hard for others on my team (or me in 6 months) to wrap their (my) head around. Hence my desire to render the pod with a templating engine to make it easily understandable and easier to maintain.

From the code examples that I read here the existing templating engine doesn't appear to have this functionality, but I am hoping that someone will prove me wrong.

Solution

you could use built in SimpleTemplateEngine:

String renderTemplate(Map binding, String template) {
    return new groovy.text.SimpleTemplateEngine().createTemplate(template).make(binding).toString()
}

def binding = [
    dockerBuild: {
        true
    },
    version: 'v1',
    kind: 'Pod',
    labels:[
        type: 'ephemeral-jenkins-agent',
        pipeline: 'generic_pipeline'
    ]
]

def template =     '''\
apiVersion: ${version}
kind: <%= kind %>
metadata:
  labels:
<% for(label in labels){ %>\
    ${label.key}: ${label.value}
<% } %>\
spec:
  containers:
  - name: alpine
    image: alpine:3.12.3
    command:
    - cat
    tty: true
<% if( dockerBuild() ){ %>\
  - name: docker
    image: docker:18.05-dind
    securityContext:
      privileged: true
    volumeMounts:
    - name: dind-storage
      mountPath: /var/lib/docker
<% } %>\
<% if( dockerBuild() ){ %>\
  volumes:
    - name: dind-storage
      emptyDir: {}
<% } else { %>\
  volumes: {}
<% } %>\
    '''

println renderTemplate(binding,template)

Answered By - daggett
Answer Checked By - Timothy Miller (JavaFixing Admin)