Lab Guide: Templating Fundamentals

Step 1 — Create a fresh chart

helm create templating-lab
cd templating-lab

Step 2 — Replace values.yaml

Overwrite values.yaml with the following content:

# values.yaml
appName: my-web-app
replicaCount: 2
image:
  repository: nginx
  tag: "1.25"
environment: staging
logLevel: debug

Step 3 — Create a ConfigMap template

Create the file templates/configmap.yaml (delete any existing template files first for a clean workspace):

rm templates/*.yaml templates/*.txt 2>/dev/null
cat > templates/configmap.yaml <<'EOF'
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-config
  namespace: {{ .Release.Namespace }}
  labels:
    app.kubernetes.io/name: {{ .Chart.Name }}
    app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
    app.kubernetes.io/managed-by: {{ .Release.Service }}
data:
  APP_NAME: {{ .Values.appName | upper | quote }}
  ENVIRONMENT: {{ .Values.environment | default "production" | quote }}
  LOG_LEVEL: {{ .Values.logLevel | default "info" | upper | quote }}
  REPLICA_INFO: {{ printf "Running %d replicas" (.Values.replicaCount | int) | quote }}
EOF

Step 4 — Render the template

helm template my-release . --namespace demo

✓ Expected Output:

---
# Source: templating-lab/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: my-release-config
  namespace: demo
  labels:
    app.kubernetes.io/name: templating-lab
    app.kubernetes.io/version: "0.1.0"
    app.kubernetes.io/managed-by: Helm
data:
  APP_NAME: "MY-WEB-APP"
  ENVIRONMENT: "staging"
  LOG_LEVEL: "DEBUG"
  REPLICA_INFO: "Running 2 replicas"

Step 5 — Test with overrides

Verify that --set overrides work and the default function activates when a value is missing:

helm template my-release . --set environment="" --set logLevel=""

✓ Expected Output (data section):

data:
  APP_NAME: "MY-WEB-APP"
  ENVIRONMENT: "production"
  LOG_LEVEL: "INFO"
  REPLICA_INFO: "Running 2 replicas"

Step 1 — Update values.yaml

Add the following to the bottom of values.yaml:

ports:
  - name: http
    containerPort: 80
    protocol: TCP
  - name: metrics
    containerPort: 9090
    protocol: TCP

env:
  - name: DATABASE_URL
    value: postgres://db:5432/app
  - name: CACHE_TTL
    value: "300"

resources:
  limits:
    cpu: 500m
    memory: 256Mi
  requests:
    cpu: 100m
    memory: 128Mi

ingress:
  enabled: true
  host: myapp.example.com

Step 2 — Create a Deployment template with range

cat > templates/deployment.yaml <<'EOF'
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Release.Name }}-app
spec:
  replicas: {{ .Values.replicaCount | default 1 }}
  selector:
    matchLabels:
      app: {{ .Release.Name }}
  template:
    metadata:
      labels:
        app: {{ .Release.Name }}
    spec:
      containers:
        - name: {{ .Chart.Name }}
          image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
          ports:
          {{- range .Values.ports }}
            - name: {{ .name }}
              containerPort: {{ .containerPort }}
              protocol: {{ .protocol | default "TCP" }}
          {{- end }}
          {{- if .Values.env }}
          env:
          {{- range .Values.env }}
            - name: {{ .name }}
              value: {{ .value | quote }}
          {{- end }}
          {{- end }}
          {{- with .Values.resources }}
          resources:
            {{- toYaml . | nindent 12 }}
          {{- end }}
EOF

Step 3 — Create a conditional Ingress template

cat > templates/ingress.yaml <<'EOF'
{{- if .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ .Release.Name }}-ingress
spec:
  rules:
    - host: {{ .Values.ingress.host | default (printf "%s.local" .Release.Name) }}
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: {{ .Release.Name }}-svc
                port:
                  number: 80
{{- end }}
EOF

Step 4 — Render and verify

helm template my-release .

✓ Expected: Deployment ports section

          ports:
            - name: http
              containerPort: 80
              protocol: TCP
            - name: metrics
              containerPort: 9090
              protocol: TCP

✓ Expected: Deployment env section

          env:
            - name: DATABASE_URL
              value: "postgres://db:5432/app"
            - name: CACHE_TTL
              value: "300"

✓ Expected: Resources section

          resources:
            limits:
              cpu: 500m
              memory: 256Mi
            requests:
              cpu: 100m
              memory: 128Mi

Step 5 — Disable ingress and verify it disappears

helm template my-release . --set ingress.enabled=false | grep -c "kind: Ingress"

✓ Expected Output:

0

Step 1 — Create a whitespace test template

cat > templates/whitespace-test.yaml <<'EOF'
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-ws-test
  labels:
    {{- if .Values.appName }}
    app: {{ .Values.appName }}
    {{- end }}
    {{- with .Values.environment }}
    env: {{ . }}
    {{- end }}
    chart: {{ .Chart.Name }}
data:
  {{- range $key, $val := .Values.env }}
  {{ $key }}_KEY: {{ $val.name | quote }}
  {{- end }}
EOF

Step 2 — Render and inspect whitespace

helm template my-release . -s templates/whitespace-test.yaml

✓ Expected Output:

---
# Source: templating-lab/templates/whitespace-test.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: my-release-ws-test
  labels:
    app: my-web-app
    env: staging
    chart: templating-lab
data:
  0_KEY: "DATABASE_URL"
  1_KEY: "CACHE_TTL"

Step 3 — Experiment: remove trim markers

Edit the template and remove all - trim markers from {{-. Re-render and observe the blank lines that appear in the output. Then restore the markers.

# See the difference
sed 's/{{-/{{/g' templates/whitespace-test.yaml > /tmp/no-trim.yaml
cp /tmp/no-trim.yaml templates/whitespace-test-notrim.yaml
helm template my-release . -s templates/whitespace-test-notrim.yaml
rm templates/whitespace-test-notrim.yaml

cd ..
rm -rf templating-lab