Helm

Overview

Helm is the package manager for Kubernetes. Charts are packages of pre-configured Kubernetes manifests with templating, making applications distributable, configurable, and upgradeable. Helm manages releases — versioned installations of charts into a cluster.

Chart Structure

my-chart/
  Chart.yaml           # Chart metadata (name, version, dependencies)
  values.yaml          # Default configuration values
  templates/
    deployment.yaml    # Templated Kubernetes manifests
    service.yaml
    ingress.yaml
    _helpers.tpl       # Reusable template snippets
    NOTES.txt          # Post-install instructions

Chart.yaml

apiVersion: v2
name: my-app
description: A Helm chart for my application
version: 1.0.0
appVersion: "2.0.0"
dependencies:
  - name: postgresql
    version: "15.x.x"
    repository: https://charts.bitnami.com/bitnami
    condition: postgresql.enabled

values.yaml

replicaCount: 3
image:
  repository: my-app
  tag: "1.0.0"
  pullPolicy: IfNotPresent

service:
  type: ClusterIP
  port: 80

ingress:
  enabled: true
  host: my-app.example.com

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

postgresql:
  enabled: true

Template Example

# templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ include "my-app.fullname" . }}
  labels:
    {{- include "my-app.labels" . | nindent 4 }}
spec:
  replicas: {{ .Values.replicaCount }}
  selector:
    matchLabels:
      {{- include "my-app.selectorLabels" . | nindent 6 }}
  template:
    metadata:
      labels:
        {{- include "my-app.selectorLabels" . | nindent 8 }}
    spec:
      containers:
        - name: {{ .Chart.Name }}
          image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
          ports:
            - containerPort: 8080
          resources:
            {{- toYaml .Values.resources | nindent 12 }}

Helper Templates

# templates/_helpers.tpl
{{- define "my-app.fullname" -}}
{{- printf "%s-%s" .Release.Name .Chart.Name | trunc 63 | trimSuffix "-" -}}
{{- end -}}

{{- define "my-app.labels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
app.kubernetes.io/version: {{ .Chart.AppVersion }}
{{- end -}}

{{- define "my-app.selectorLabels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
{{- end -}}

Key Commands

# Install a release
helm install my-release ./my-chart -f custom-values.yaml

# Upgrade a release
helm upgrade my-release ./my-chart -f prod-values.yaml

# Dry run (preview rendered manifests)
helm template my-release ./my-chart -f values.yaml

# Lint a chart
helm lint ./my-chart

# Show computed values
helm get values my-release

# Rollback
helm rollback my-release 1

# Uninstall
helm uninstall my-release

Common Template Functions

Best Practices

• Always run helm template or helm install --dry-run to preview rendered manifests before deploying.
• Use _helpers.tpl for shared templates (labels, names, selectors) to keep DRY.
• Use values.yaml for defaults and -f flag for environment overrides.
• Pin chart dependency versions to avoid breaking changes.
• Use helm lint in CI to catch template errors early.
• Use Helm's built-in required function to fail fast on missing values.
• Use semantic versioning for chart versions and appVersion for the application version.