Kubernetes/Helm: When are ConfigMap functions called?

If I have a ConfigMap like so:

apiVersion: v1
kind: ConfigMap
metadata:
  name: id-config
data:
  uuid: "{{ randAlphaNum 32 }}"

and a StatefulSet specification like so (taken and slightly modified from kubernetes' StatefulSet Basics page):

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: registry.k8s.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
      env:
      - name: UUID
        valueFrom:
          configMapKeyRef:
            name: id-config
            key: uuid
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

Will randAlphaNum only be called once, when the initial deployment occurs, and then the value returned by randAlphaNum is stored in the uuid key and used if a pod restarts? Or will randAlphaNum be called every time a pod is created or restarted, with a different uuid being returned every time? Thanks in advance.

When you deploy something with Helm you need to differentiate between two distinct things that are happening:

1. Rendering the manifests, which happens locally on the machine where you execute the helm CLI.
2. Deploying the rendered manifests. I.e. sending the instruction to the Kubernetes API to deploy certain resources.

Entries in the manifest files such as {{ randAlphaNum 32 }} are rendered in step 1 and the pre-rendered results are sent to the Kubernetes API. It will only change if you ask Helm to render and deploy again.