Helm serves as a comprehensive package management solution for Kubernetes, functioning similarly to package managers like yum or apt in Linux environments. It simplifies the deployment of pre-packaged applications to Kubernetes clusters, which traditionally required managing numerous YAML files for complex applications.

Core Helm Components

• Helm Client: A command-line interface tool designed for creating, packaging, publishing, and managing Kubernetes application charts.
• Chart: A collection of files that describe a related set of Kubernetes resources. It acts as a blueprint for deploying applications.
• Release: An instance of a chart deployed to Kubernetes. Each time a chart is deployed, it creates a release that generates actual running resources in the cluster.

Installing the Helm Client

To get started with Helm, download the appropriate binary for your system:

wget https://get.helm.sh/helm-v3.8.0-linux-amd64.tar.gz
tar -zxvf helm-v3.8.0-linux-amd64.tar.gz
sudo mv linux-amd64/helm /usr/local/bin/

Essential Helm Commands

Configuring Chart Repositories

Add repoistories to access pre-built charts:

helm repo add azure-charts https://mirror.azure.cn/kubernetes/charts
helm repo add aliyun-charts https://kubernetes.oss-cn-hangzhou.aliyuncs.com/charts
helm repo update

List available repositories:

helm repo list
helm search repo azure-charts

Remove a repository when needed:

helm repo remove aliyun-charts

Basic Helm Operations

Discovering Charts

Search for available charts:

helm search repo
helm search repo postgresql

Inspecting Charts

Examine chart details before installation:

helm show chart azure-charts/postgresql

Installing Charts

Deploy a chart to your cluster:

helm install database azure-charts/postgresql

Check the deployment status:

helm status database

Customizing Chart Configuration

You can customize chart installations using two approaches:

1. Using a values file:

   helm show values azure-charts/mysql > custom-values.yaml
   # Edit custom-values.yaml
   helm install db -f custom-values.yaml azure-charts/mysql
   
   

2. Using command-line parameters:

   helm install db --set imageTag=1.20.0 --set persistence.size=10Gi azure-charts/mysql
   
   

Creating Custom Charts

Generate a new chart template:

helm create myapp-chart

The chart structure includes:

• Chart.yaml: Contains metadata about the chart (name, version, description)
• values.yaml: Default values for template variables
• templates/: Directory for Kubernetes manifest templates
• charts/: Contains dependent charts
• NOTES.txt: Usage instructions displayed after installation
• _helpers.tpl: Reusable template helpers

Chart Template Example

Modify templates/deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Release.Name }}-app
spec:
  replicas: {{ .Values.replicaCount }}
  selector:
    matchLabels:
      app: {{ .Chart.Name }}
  template:
    metadata:
      labels:
        app: {{ .Chart.Name }}
    spec:
      containers:
      - name: {{ .Chart.Name }}
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        ports:
        - containerPort: {{ .Values.service.port }}

Managing Releases

Upgrading Releases

Update an existing release:

helm upgrade --set image.tag=1.21.0 myapp myapp-chart
helm upgrade -f new-values.yaml myapp myapp-chart

Rolling Back Releases

If an upgrade doesn't work as expected, revert to a previous version:

helm history myapp
helm rollback myapp 2

Uninstalling Releases

Remove a release from the cluster:

helm uninstall myapp

Template Debugging

Validate templates without deploying:

helm install --dry-run --debug myapp ./myapp-chart

Helm Template Objects

Helm provides several built-in objects for templates:

Working with Values

Values can be sourced from multiple locations, with precedence:

1. Chart's values.yaml
2. Parent chart's values
3. Values files specified with -f or --values
4. Command-line --set parameters

Example values file (values.yaml):

replicaCount: 3
image:
  repository: nginx
  tag: 1.21.0
  pullPolicy: IfNotPresent
service:
  type: ClusterIP
  port: 80
resources:
  limits:
    cpu: 100m
    memory: 128Mi

Conditional Logic in Templates

Use conditionals to control template rendering:

{{- if eq .Values.env "production" }}
  env:
    - name: ENV
      value: "prod"
{{- else if eq .Values.env "staging" }}
  env:
    - name: ENV
      value: "stage"
{{- else }}
  env:
    - name: ENV
      value: "dev"
{{- end }}

Template Functions and Pipelines

Helm supports various template functions:

# Indentation
spec:
  {{- .Values.resources | indent 8 }}

# String manipulation
name: {{ upper .Values.appName }}
title: {{ title .Values.appName }}

# Numeric operations
count: {{ add .Values.replicaCount 1 }}

Using 'with' for Scoped Templates

Restrict the scope of a variable:

{{- with .Values.service }}
  type: {{ .type }}
  port: {{ .port }}
{{- end }}

Iterating with Range

Process arrays or maps:

env:
{{- range $key, $value := .Values.environmentVariables }}
  - name: {{ $key }}
    value: {{ $value | quote }}
{{- end }}

Creating Shared Templates

Define reusable templates in _helpers.tpl:

{{/* Define a named template */}}
{{- define "myapp.fullname" -}}
{{- .Chart.Name }}-{{ .Release.Name }}
{{- end }}

{{/* Use the template */}}
metadata:
  name: {{ template "myapp.fullname" . }}

Include templates with specific context:

{{- include "myapp.commonLabels" . | indent 4 }}

By mastering these Helm techniques, you can efficiently manage Kubernetes applications through reusable, versioned packages that simplify deployment and maintenance processes.