Overview

Working with Helm templates and template functions.

Basic Templating

Values Access

apiVersion: v1
kind: Pod
metadata:
  name: {{ .Values.name }}
  namespace: {{ .Release.Namespace }}
spec:
  containers:
  - name: {{ .Chart.Name }}
    image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"

Built-in Objects

• .Values: Values from values.yaml and overrides
• .Release: Release information (Name, Namespace, IsUpgrade, IsInstall)
• .Chart: Chart metadata from Chart.yaml
• .Files: Access non-template files in chart
• .Capabilities: Kubernetes cluster capabilities
• .Template: Current template information

Template Functions

String Functions

# upper, lower, title
name: {{ .Values.name | upper }}

# quote
value: {{ .Values.password | quote }}

# trimSuffix, trimPrefix
image: {{ .Values.image | trimSuffix ":latest" }}

# replace
url: {{ .Values.url | replace "http" "https" }}

Default Values

# default function
port: {{ .Values.port | default 8080 }}
tag: {{ .Values.image.tag | default .Chart.AppVersion }}

# required function
database: {{ required "database.host is required" .Values.database.host }}

Type Conversion

# toString, toJson, toYaml
replicas: {{ .Values.replicas | toString }}

annotations:
{{ toYaml .Values.annotations | indent 2 }}

config: |
{{ toJson .Values.config | indent 2 }}

Conditionals

{{- if .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ .Release.Name }}
spec:
  # ...
{{- end }}

{{- if and .Values.persistence.enabled .Values.persistence.existingClaim }}
# Use existing claim
{{- else if .Values.persistence.enabled }}
# Create new claim
{{- end }}

Loops

{{- range .Values.environments }}
- name: {{ .name }}
  value: {{ .value | quote }}
{{- end }}

{{- range $key, $value := .Values.config }}
{{ $key }}: {{ $value | quote }}
{{- end }}

Named Templates (_helpers.tpl)

Define Templates

{{/*
Common labels
*/}}
{{- define "mychart.labels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
{{- end }}

{{/*
Selector labels
*/}}
{{- define "mychart.selectorLabels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
{{- end }}

Use Templates

metadata:
  labels:
    {{- include "mychart.labels" . | nindent 4 }}
spec:
  selector:
    matchLabels:
      {{- include "mychart.selectorLabels" . | nindent 6 }}

Flow Control

With

{{- with .Values.service }}
apiVersion: v1
kind: Service
metadata:
  name: {{ .name }}
spec:
  type: {{ .type }}
  ports:
  - port: {{ .port }}
{{- end }}

Range with Index

{{- range $index, $value := .Values.items }}
item-{{ $index }}: {{ $value }}
{{- end }}

Whitespace Control

# Remove leading whitespace
{{- .Values.name }}

# Remove trailing whitespace
{{ .Values.name -}}

# Remove both
{{- .Values.name -}}

Files Access

Read Files

config: |
{{ .Files.Get "config/app.conf" | indent 2 }}

Glob Files

{{- range $path, $content := .Files.Glob "config/*.yaml" }}
{{ $path }}: |
{{ $content | indent 2 }}
{{- end }}

Advanced Functions

Ternary

environment: {{ ternary "production" "development" .Values.production }}

Coalesce

# Returns first non-empty value
port: {{ coalesce .Values.service.port .Values.port 8080 }}

List Functions

# list, append, prepend, concat
args:
{{- range list "arg1" "arg2" "arg3" }}
  - {{ . }}
{{- end }}

Dict Functions

# dict, set, unset, hasKey
{{- $config := dict "key1" "value1" "key2" "value2" }}
{{- if hasKey $config "key1" }}
found: true
{{- end }}

Debugging

# Print debug info
{{ printf "%#v" .Values | indent 2 }}

# Fail on purpose to see values
{{ fail (printf "Debug: %#v" .Values) }}

Best Practices

Use Helpers for Repeated Logic

{{- define "mychart.fullname" -}}
{{- if .Values.fullnameOverride }}
{{- .Values.fullnameOverride | trunc 63 | trimSuffix "-" }}
{{- else }}
{{- printf "%s-%s" .Release.Name .Chart.Name | trunc 63 | trimSuffix "-" }}
{{- end }}
{{- end }}

Validate Input

{{- if not (has .Values.service.type (list "ClusterIP" "NodePort" "LoadBalancer")) }}
{{- fail "service.type must be ClusterIP, NodePort, or LoadBalancer" }}
{{- end }}

Quote String Values

# Always quote strings
value: {{ .Values.string | quote }}