Helm Chart Development

Helm Chart Development

Create and structure Helm charts following best practices, including templating, values design, and chart architecture.

Keywords

helm, chart, development, templating, template, values, schema, kubernetes, packaging, creating, create, scaffold, scaffolding, helpers, deployment, deploying, writing, designing, structure

When to Use This Skill

• Creating new Helm charts from scratch
• Designing values.yaml schema and structure
• Implementing Helm template patterns
• Setting up chart directory structure
• Writing template helpers (_helpers.tpl)
• Creating values.schema.json validation

Related Skills

• helm-chart-maintenance - Versioning and updates
• helm-chart-review - Quality and security review
• k8s-security-hardening - Security best practices
• Shared: Pod Security Context

Quick Reference

Chart Structure

Standard Layout

mychart/
├── Chart.yaml
├── Chart.lock
├── values.yaml
├── values.schema.json
├── README.md
├── LICENSE
├── .helmignore
├── templates/
│   ├── NOTES.txt
│   ├── _helpers.tpl
│   ├── deployment.yaml
│   ├── service.yaml
│   ├── ingress.yaml
│   ├── configmap.yaml
│   ├── secret.yaml
│   ├── serviceaccount.yaml
│   ├── hpa.yaml
│   └── tests/
│       └── test-connection.yaml
├── charts/
└── crds/

Chart.yaml

Complete Example

apiVersion: v2
name: myapp
description: A Helm chart for MyApp
type: application
version: 1.0.0
appVersion: "2.3.1"

home: https://github.com/org/myapp
icon: https://example.com/icon.png
sources:
  - https://github.com/org/myapp

maintainers:
  - name: Platform Team
    email: platform@company.com
    url: https://platform.company.com

keywords:
  - app
  - web

annotations:
  artifacthub.io/changes: |
    - kind: added
      description: Initial release
  artifacthub.io/license: Apache-2.0

dependencies:
  - name: postgresql
    version: "12.x.x"
    repository: https://charts.bitnami.com/bitnami
    condition: postgresql.enabled
    tags:
      - database
  - name: redis
    version: "17.x.x"
    repository: https://charts.bitnami.com/bitnami
    condition: redis.enabled
    import-values:
      - child: primary
        parent: redis

Values Design

Well-Structured values.yaml

# -- Number of replicas
replicaCount: 1

image:
  # -- Image repository
  repository: myapp
  # -- Image pull policy
  pullPolicy: IfNotPresent
  # -- Image tag (defaults to appVersion)
  tag: ""

# -- Image pull secrets
imagePullSecrets: []
# -- Override chart name
nameOverride: ""
# -- Override full name
fullnameOverride: ""

serviceAccount:
  # -- Create service account
  create: true
  # -- Service account annotations
  annotations: {}
  # -- Service account name (generated if not set)
  name: ""
  # -- Automount service account token
  automount: true

# -- Pod annotations
podAnnotations: {}

# -- Pod labels
podLabels: {}

podSecurityContext:
  fsGroup: 1000
  runAsNonRoot: true

securityContext:
  allowPrivilegeEscalation: false
  readOnlyRootFilesystem: true
  runAsNonRoot: true
  runAsUser: 1000
  capabilities:
    drop:
      - ALL

service:
  # -- Service type
  type: ClusterIP
  # -- Service port
  port: 80
  # -- Target port
  targetPort: 8080
  # -- Node port (when type is NodePort)
  nodePort: ""

ingress:
  # -- Enable ingress
  enabled: false
  # -- Ingress class name
  className: ""
  # -- Ingress annotations
  annotations: {}
  # -- Ingress hosts
  hosts:
    - host: chart-example.local
      paths:
        - path: /
          pathType: Prefix
  # -- Ingress TLS configuration
  tls: []

resources:
  limits:
    cpu: 500m
    memory: 512Mi
  requests:
    cpu: 100m
    memory: 128Mi

autoscaling:
  enabled: false
  minReplicas: 1
  maxReplicas: 10
  targetCPUUtilizationPercentage: 80
  targetMemoryUtilizationPercentage: 80

# -- Node selector
nodeSelector: {}

# -- Tolerations
tolerations: []

# -- Affinity rules
affinity: {}

# -- Extra environment variables
extraEnv: []

# -- Extra volume mounts
extraVolumeMounts: []

# -- Extra volumes
extraVolumes: []

# -- Liveness probe configuration
livenessProbe:
  httpGet:
    path: /healthz
    port: http
  initialDelaySeconds: 10
  periodSeconds: 10

# -- Readiness probe configuration
readinessProbe:
  httpGet:
    path: /ready
    port: http
  initialDelaySeconds: 5
  periodSeconds: 5

# Subchart configuration
postgresql:
  enabled: false
  auth:
    database: myapp
    username: myapp

Template Helpers (_helpers.tpl)

{{/*
Expand the name of the chart.
*/}}
{{- define "myapp.name" -}}
{{- default .Chart.Name .Values.nameOverride | trunc 63 | trimSuffix "-" }}
{{- end }}

{{/*
Create a default fully qualified app name.
*/}}
{{- define "myapp.fullname" -}}
{{- if .Values.fullnameOverride }}
{{- .Values.fullnameOverride | trunc 63 | trimSuffix "-" }}
{{- else }}
{{- $name := default .Chart.Name .Values.nameOverride }}
{{- if contains $name .Release.Name }}
{{- .Release.Name | trunc 63 | trimSuffix "-" }}
{{- else }}
{{- printf "%s-%s" .Release.Name $name | trunc 63 | trimSuffix "-" }}
{{- end }}
{{- end }}
{{- end }}

{{/*
Create chart name and version for chart label.
*/}}
{{- define "myapp.chart" -}}
{{- printf "%s-%s" .Chart.Name .Chart.Version | replace "+" "_" | trunc 63 | trimSuffix "-" }}
{{- end }}

{{/*
Common labels
*/}}
{{- define "myapp.labels" -}}
helm.sh/chart: {{ include "myapp.chart" . }}
{{ include "myapp.selectorLabels" . }}
{{- if .Chart.AppVersion }}
app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
{{- end }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
{{- end }}

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

{{/*
Create the name of the service account to use
*/}}
{{- define "myapp.serviceAccountName" -}}
{{- if .Values.serviceAccount.create }}
{{- default (include "myapp.fullname" .) .Values.serviceAccount.name }}
{{- else }}
{{- default "default" .Values.serviceAccount.name }}
{{- end }}
{{- end }}

{{/*
Return the proper image name
*/}}
{{- define "myapp.image" -}}
{{- $tag := .Values.image.tag | default .Chart.AppVersion -}}
{{- printf "%s:%s" .Values.image.repository $tag }}
{{- end }}

Template Patterns

Deployment Template

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ include "myapp.fullname" . }}
  labels:
    {{- include "myapp.labels" . | nindent 4 }}
spec:
  {{- if not .Values.autoscaling.enabled }}
  replicas: {{ .Values.replicaCount }}
  {{- end }}
  selector:
    matchLabels:
      {{- include "myapp.selectorLabels" . | nindent 6 }}
  template:
    metadata:
      annotations:
        checksum/config: {{ include (print $.Template.BasePath "/configmap.yaml") . | sha256sum }}
        {{- with .Values.podAnnotations }}
        {{- toYaml . | nindent 8 }}
        {{- end }}
      labels:
        {{- include "myapp.labels" . | nindent 8 }}
        {{- with .Values.podLabels }}
        {{- toYaml . | nindent 8 }}
        {{- end }}
    spec:
      {{- with .Values.imagePullSecrets }}
      imagePullSecrets:
        {{- toYaml . | nindent 8 }}
      {{- end }}
      serviceAccountName: {{ include "myapp.serviceAccountName" . }}
      securityContext:
        {{- toYaml .Values.podSecurityContext | nindent 8 }}
      containers:
        - name: {{ .Chart.Name }}
          securityContext:
            {{- toYaml .Values.securityContext | nindent 12 }}
          image: {{ include "myapp.image" . }}
          imagePullPolicy: {{ .Values.image.pullPolicy }}
          ports:
            - name: http
              containerPort: {{ .Values.service.targetPort }}
              protocol: TCP
          {{- with .Values.livenessProbe }}
          livenessProbe:
            {{- toYaml . | nindent 12 }}
          {{- end }}
          {{- with .Values.readinessProbe }}
          readinessProbe:
            {{- toYaml . | nindent 12 }}
          {{- end }}
          resources:
            {{- toYaml .Values.resources | nindent 12 }}
          {{- with .Values.extraEnv }}
          env:
            {{- toYaml . | nindent 12 }}
          {{- end }}
          {{- with .Values.extraVolumeMounts }}
          volumeMounts:
            {{- toYaml . | nindent 12 }}
          {{- end }}
      {{- with .Values.extraVolumes }}
      volumes:
        {{- toYaml . | nindent 8 }}
      {{- end }}
      {{- with .Values.nodeSelector }}
      nodeSelector:
        {{- toYaml . | nindent 8 }}
      {{- end }}
      {{- with .Values.affinity }}
      affinity:
        {{- toYaml . | nindent 8 }}
      {{- end }}
      {{- with .Values.tolerations }}
      tolerations:
        {{- toYaml . | nindent 8 }}
      {{- end }}

Conditional Resource

{{- if .Values.ingress.enabled -}}
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ include "myapp.fullname" . }}
  labels:
    {{- include "myapp.labels" . | nindent 4 }}
  {{- with .Values.ingress.annotations }}
  annotations:
    {{- toYaml . | nindent 4 }}
  {{- end }}
spec:
  {{- if .Values.ingress.className }}
  ingressClassName: {{ .Values.ingress.className }}
  {{- end }}
  {{- if .Values.ingress.tls }}
  tls:
    {{- range .Values.ingress.tls }}
    - hosts:
        {{- range .hosts }}
        - {{ . | quote }}
        {{- end }}
      secretName: {{ .secretName }}
    {{- end }}
  {{- end }}
  rules:
    {{- range .Values.ingress.hosts }}
    - host: {{ .host | quote }}
      http:
        paths:
          {{- range .paths }}
          - path: {{ .path }}
            pathType: {{ .pathType }}
            backend:
              service:
                name: {{ include "myapp.fullname" $ }}
                port:
                  number: {{ $.Values.service.port }}
          {{- end }}
    {{- end }}
{{- end }}

Values Schema (values.schema.json)

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["image"],
  "properties": {
    "replicaCount": {
      "type": "integer",
      "minimum": 1,
      "description": "Number of replicas"
    },
    "image": {
      "type": "object",
      "required": ["repository"],
      "properties": {
        "repository": {
          "type": "string",
          "description": "Image repository"
        },
        "tag": {
          "type": "string",
          "description": "Image tag"
        },
        "pullPolicy": {
          "type": "string",
          "enum": ["Always", "IfNotPresent", "Never"],
          "default": "IfNotPresent"
        }
      }
    },
    "resources": {
      "type": "object",
      "properties": {
        "limits": {
          "type": "object",
          "properties": {
            "cpu": { "type": "string" },
            "memory": { "type": "string" }
          }
        },
        "requests": {
          "type": "object",
          "properties": {
            "cpu": { "type": "string" },
            "memory": { "type": "string" }
          }
        }
      }
    }
  }
}

NOTES.txt Template

{{- $fullName := include "myapp.fullname" . -}}
1. Get the application URL by running these commands:
{{- if .Values.ingress.enabled }}
{{- range $host := .Values.ingress.hosts }}
  {{- range .paths }}
  http{{ if $.Values.ingress.tls }}s{{ end }}://{{ $host.host }}{{ .path }}
  {{- end }}
{{- end }}
{{- else if contains "NodePort" .Values.service.type }}
  export NODE_PORT=$(kubectl get --namespace {{ .Release.Namespace }} -o jsonpath="{.spec.ports[0].nodePort}" services {{ $fullName }})
  export NODE_IP=$(kubectl get nodes --namespace {{ .Release.Namespace }} -o jsonpath="{.items[0].status.addresses[0].address}")
  echo http://$NODE_IP:$NODE_PORT
{{- else if contains "LoadBalancer" .Values.service.type }}
  NOTE: It may take a few minutes for the LoadBalancer IP to be available.
  Watch status: kubectl get --namespace {{ .Release.Namespace }} svc -w {{ $fullName }}
  export SERVICE_IP=$(kubectl get svc --namespace {{ .Release.Namespace }} {{ $fullName }} --template "{{"{{ range (index .status.loadBalancer.ingress 0) }}{{.}}{{ end }}"}}")
  echo http://$SERVICE_IP:{{ .Values.service.port }}
{{- else if contains "ClusterIP" .Values.service.type }}
  kubectl --namespace {{ .Release.Namespace }} port-forward svc/{{ $fullName }} 8080:{{ .Values.service.port }}
  echo "Visit http://127.0.0.1:8080"
{{- end }}

Templating Tips

Whitespace Control

# Use {{- and -}} to trim whitespace
{{- if .Values.enabled }}
key: value
{{- end }}

# Use nindent for proper indentation
labels:
  {{- include "myapp.labels" . | nindent 2 }}

Required Values

# Fail if value not set
image: {{ required "image.repository is required" .Values.image.repository }}

Default Values

# Provide default
port: {{ .Values.port | default 8080 }}

# Coalesce (first non-empty)
name: {{ coalesce .Values.name .Values.nameOverride .Chart.Name }}

Loops and Ranges

# Range over list
{{- range .Values.hosts }}
- {{ . | quote }}
{{- end }}

# Range with index
{{- range $index, $host := .Values.hosts }}
- name: host-{{ $index }}
  value: {{ $host }}
{{- end }}

# Range over map
{{- range $key, $value := .Values.env }}
- name: {{ $key }}
  value: {{ $value | quote }}
{{- end }}

CLI Commands

# Create new chart
helm create mychart

# Lint chart
helm lint mychart/

# Template locally (dry-run)
helm template myrelease mychart/ -f values.yaml

# Package chart
helm package mychart/

# Install with debug
helm install myrelease mychart/ --debug --dry-run