Helm Charts

Introduction

A Helm chart is a structured collection of files defining a Kubernetes application.

Why build our own charts?

• Off-the-shelf, well-maintained charts may not exist for your specific application.
• Versioning makes it easier to upgrade and rollback the many related objects of an application.
• Custom charts allow you to define deployment configurations tailored to your app.
• Enforce organizational policies and best practices, allowing teams to standardize how applications are deployed within your organization.
• Control over all Kubernetes resources and their configurations, with the possibility of implementing custom logic in the templates.
• Reuse existing charts (either community or private) as dependencies for complex applications, while following best practices.
• Templating: Avoids redundant YAML definitions by using reusable templates.
• Dependency Management: Helps manage application dependencies efficiently.

Helm Chart Structure

• A Helm chart is a structured collection of files defining a Kubernetes application. The typical structure of a Helm chart looks like this:

mychart/
├── charts/             # Subcharts (dependencies)
├── templates/          # Templated YAML files
│   ├── /tests          # Tests to be executed using helm test     
│   ├── deployment.yaml
│   ├── service.yaml
│   ├── _helpers.tpl    # Reusable template functions
│   ├── ingress.yaml    # Ingress resource (optional)
│   └── NOTES.txt       # Post-installation instructions
├── values.yaml         # Default configuration values
├── Chart.yaml          # Metadata about the chart
├── README.md           # Documentation
└── Notes.txt           # Contents printed upon successful chart installation or upgrade.

Key Files Explained

File/Directory	Description
Chart.yaml	Contains metadata like name, version, and description of the chart.
values.yaml	Defines the default values for templates.
templates/	Contains Kubernetes resource templates with placeholders.
charts/	Holds dependencies (subcharts).
README.md	Provides documentation about the chart.

• Chart.yaml
  • A YAML file containing metadata about the chart. Among other fields, allows us to set:
  • apiVersion: The chart API version (vl or v2). For Helm 3, use v2.
  • name: The name of the chart
  • version: The version of the chart (uses •semantic versioning).
  • description: A brief description of the chart.
  • type: Type of chart (e.g., application or library).
  • keywords: A list of keywords representative of the project.
  • dependencies: A list of other charts that the current chart depends on.

Creating Your First Helm Chart

• Let’s create a simple Helm chart for a web application.

Step 1: Install Helm

• Ensure Helm is installed on your machine:

helm version

Step 2: Create a Helm Chart

• Run the following command to create a new chart:

helm create mychart

Step 3: Modify values.yaml

• Update values.yaml to define custom values:

replicaCount: 2
image:
  repository: nginx
  tag: latest
  pullPolicy: IfNotPresent
service:
  type: ClusterIP
  port: 80

Step 4: Install the Helm Chart

• Deploy the chart to a Kubernetes cluster:

helm install my-release ./mychart

Step 5: Verify the Deployment

• Check the installed release:

helm list

Step 6: Upgrade or Uninstall

• Upgrade the release:

helm upgrade my-release ./mychart

• Uninstall the release:

helm uninstall my-release

Conclusion

Helm charts simplify Kubernetes application deployment by providing a structured approach to packaging, managing, and upgrading applications. Whether you are deploying microservices, databases, or entire applications, Helm offers a scalable and maintainable solution.