Kubernetes - Creating Custom Helm Charts

Introduction

Helm charts are a powerful way to define, install, and manage Kubernetes applications. This guide provides an advanced understanding of creating custom Helm charts to package and deploy your Kubernetes applications efficiently.

Creating a New Helm Chart

To create a new Helm chart, use the helm create command. This command generates a boilerplate structure for your chart:

# Create a new Helm chart
helm create mychart

# Navigate to the chart directory
cd mychart

# View the generated files
tree .
                

Understanding Helm Chart Structure

A Helm chart consists of several files and directories. Here is an overview of the key components:

• Chart.yaml: Contains metadata about the chart, such as its name, version, and description.
• values.yaml: Defines the default configuration values for the chart.
• charts/: Contains any dependencies for the chart.
• templates/: Contains the template files that define the Kubernetes resources.
• templates/_helpers.tpl: Contains helper templates that can be used across the chart.

# Example of a Helm chart directory structure
mychart/
  Chart.yaml    # A YAML file containing information about the chart
  values.yaml   # The default configuration values for this chart
  charts/       # A directory containing any charts upon which this chart depends
  templates/    # A directory of templates that, when combined with values, will generate valid Kubernetes manifest files
  templates/_helpers.tpl # A file containing helper templates
                

Customizing Templates

Templates are the core of Helm charts. They define the Kubernetes resources that will be deployed. Templates use the Go template language and can include logic, loops, and conditionals. Here is an example of a simple template:

# templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Release.Name }}-{{ .Chart.Name }}
  labels:
    app: {{ .Chart.Name }}
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:
        - name: http
          containerPort: 80
        resources:
          requests:
            memory: "{{ .Values.resources.requests.memory }}"
            cpu: "{{ .Values.resources.requests.cpu }}"
          limits:
            memory: "{{ .Values.resources.limits.memory }}"
            cpu: "{{ .Values.resources.limits.cpu }}"
                

Using Values in Templates

The values.yaml file contains default configuration values that can be overridden during installation. These values are referenced in templates using the .Values object. Here is an example:

# values.yaml
replicaCount: 2

image:
  repository: nginx
  tag: stable
  pullPolicy: IfNotPresent

resources:
  requests:
    memory: "64Mi"
    cpu: "250m"
  limits:
    memory: "128Mi"
    cpu: "500m"
                

Testing and Linting Helm Charts

Before deploying your Helm chart, it is important to test and lint it to ensure there are no errors. Helm provides commands for this purpose:

# Lint the chart
helm lint mychart

# Test the chart
helm install --dry-run --debug my-release ./mychart
                

Publishing Helm Charts

Once your Helm chart is ready, you can publish it to a Helm repository to share it with others. Here is an example of packaging and publishing a chart:

# Package the chart
helm package mychart

# Index the chart (assuming a GitHub Pages repository)
helm repo index .

# Push the packaged chart and index file to the repository
# (This step will vary depending on your repository setup)
                

Best Practices

Follow these best practices when creating custom Helm charts:

• Use Semantic Versioning: Follow semantic versioning for your charts to communicate changes effectively.
• Keep Charts DRY: Avoid duplication by using helper templates and including common configuration in values.yaml.
• Document Your Charts: Provide clear documentation and examples for your charts to help users understand how to use them.
• Test Thoroughly: Test your charts in a staging environment and use Helm's testing and linting tools to catch errors early.
• Automate Releases: Use CI/CD pipelines to automate the packaging, testing, and publishing of your charts.

Conclusion

This guide provided an advanced overview of creating custom Helm charts, including defining templates, using values, testing, and publishing charts. By following best practices and leveraging the power of Helm, you can efficiently manage the deployment and lifecycle of your Kubernetes applications.