Introduction

Templating in Helm enables you to dynamically generate Kubernetes manifests using Go templates. Instead of hardcoding values (e.g., replicas, image tags), you can use placeholders and inject values from a values.yaml file or directly from the command line during deployment.

This makes charts flexible, reusable, and environment-agnostic.

Key Features of Helm Templating:

Dynamic Resource Creation: Templates generate Kubernetes YAML dynamically based on input values.
Reusable Snippets: Helper templates allow code reuse and easier maintenance.
Customization: Values from values.yaml or overrides provide tailored configurations for different environments (e.g., dev, staging, production).
Logic and Conditionals: Add loops, conditionals, and functions to your templates for complex customizations.

Helm templating bridges the gap between static YAML files and the dynamic nature of application environments, making Kubernetes resource management simpler and more efficient.

Built in objects

built-in objects are pre-defined objects that provide access to various types of data during the rendering process. These objects make it easier to template Kubernetes manifests and manage Helm charts dynamically.

Below is a list of common built-in objects in Helm:

Release: Contains information about the release (e.g., name, namespace, and revision).
Values: Represents the values passed into the chart, either from values.yaml or via --set
Chart: Provides metadata about the chart
Files: Gives access to non-template files in the charts directory.
Capabilities: Provides information about the Kubernetes cluster's capabilities

config-map.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-config
  namespace: {{ .Release.Namespace }}
data:
  app_version: {{ .Chart.Version }}
  cluster_version: {{ .Capabilities.KubeVersion.Version }}

# Run following command to see the changes
helm install app ./app OR helm upgrade app ./app # install new or update existing release
kubectl get configmap app-config -oyaml # view details of the config map

Variables, Conditionals And Range

Variables: Define variables with {{- $var := value -}} and reuse them in templates, e.g., app_environment: {{ $env | quote }}.
Conditionals: Use if, else if, and else to handle logic, e.g., render resources based on .Values.
Range: Loop through lists/maps with range, e.g., {{- range $key, $value := .Values.config -}}.

config-map.yaml

{{- $serviceName := .Release.Name }} # Basic variable definition
{{- $fullName := printf "%s-%s" .Release.Name .Chart.Name }} # Interpolation
{{- $isProd := eq .Values.environment "production" }} # DRY 
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-config
  namespace: {{ .Release.Namespace }}
data:
  app_version: {{ .Chart.Version }}
  cluster_version: {{ .Capabilities.KubeVersion.Version }}
  service_name: {{ $serviceName }}
  full_name: {{ $fullName }}
  {{- if $isProd }} # Conditionally create section of the k8s object
  priority: Highest
  {{- else  }}
  priority: Low
  {{- end }} 
  {{- range $key, $value := .Values.config.data }} # Looping
  {{ $key }}: {{ $value | quote }}
  {{- end }}

values.yaml

config:
  config-name: "app-config"
  data:
    key1: "value1"
    key2: "value2"

environment: "dev"

redis:
  enabled: false
  auth:
    password: "securepassword"

Functions

Helm templates provide several built-in functions that can be used to manipulate values, perform logic, and format output.

Below are some commonly used template functions:

quote: Quotes a string.
```
{{ .Values.name | quote }}
```
default: Provides a default value if the value is empty or not set.
```
{{ .Values.name | default "default-name" }}
```
len: Returns the length of a string, list, or map.
```
{{ len .Values.items }}
```
required: Ensures a value is provided; otherwise, it throws an error.
```
{{ required "Value for name is required" .Values.name }}
```

cat: Concatenates multiple strings.

{{ .Values.firstName | cat " " .Values.lastName }}

and: Logical AND.

{{ and (eq .Values.env "prod") (eq .Values.region "us-east-1") }}

split: Splits a string into a list by a delimiter.
```
{{ .Values.name | split "-" }}
```
index: Accesses a specific element in a list or map.
```
{{ index .Values.items 0 }}  # First item
```
add: Adds two values.
```
{{ add 2 3 }}  # Result: 5
```
date: Formats the current date.
```
{{ now | date "2006-01-02" }}
```

Dependencies

they allow one chart to rely on another for shared resources or functionality. This feature makes it easy to reuse and manage related components.

Definition

Chart.yaml

.
.
.
dependencies:
   - name: redis
      version: "17.0.0"
      repository: "https://charts.bitnami.com/bitnami"

# fetches the specified charts from their repositories and puts them in charts/ directory
helm dependency update

Debugging

Dry run: The helm install and helm upgrade commands have a --dry-run option to simulate the release without actually applying it to the Kubernetes cluster.
```
helm install my-release ./app --dry-run
```
flag --debug: The --debug flag with helm commands provides detailed output
```
helm template ./app --debug
```
Linting: Use helm lint to validate the chart's structure and ensure it meets Helm's best practices.
```
helm lint ./app
```

Thanks for reading!