Helmlet

📝 What is Helmlet?

Helmlet is a lightweight, fast, and flexible templating engine for YAML files, designed as a simpler alternative to Helm for Kubernetes manifests. While Helm offers a complete package management solution for Kubernetes, Helmlet focuses solely on the templating aspect with minimal dependencies.

❓ Why use Helmlet?

• Simplicity: Focused only on templating without the complexity of a full package manager
• Speed: Minimal dependencies and fast execution for quick rendering
• Flexibility: Support for multiple templates and value files with intuitive overriding
• Familiarity: Uses the same templating syntax as Helm for easy adoption
• Portability: Single binary with no external dependencies

Core Functionality

Helmlet takes values from YAML files and/or command-line parameters, processes one or more template files, and generates rendered YAML output suitable for direct application to Kubernetes or other YAML-based systems.

🚀 Quick Start

Get started with Helmlet in minutes:

1. Download the binary or build from source

   # Build from source
   go build -ldflags "-X main.Version=$(git describe --tags --always)" -o helmlet

2. Create a simple template (template.yaml)

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: {{ .Values.name }}
   spec:
     replicas: {{ .Values.replicas }}
     selector:
       matchLabels:
         app: {{ .Values.name }}
     template:
       metadata:
         labels:
           app: {{ .Values.name }}
       spec:
         containers:
         - name: {{ .Values.name }}
           image: {{ .Values.image.repository }}:{{ .Values.image.tag }}
           ports:
           - containerPort: {{ .Values.containerPort }}

3. Create a values file (values.yaml)

   name: myapp
   replicas: 3
   image:
     repository: nginx
     tag: latest
   containerPort: 80

4. Render the template

   ./helmlet --template template.yaml --value values.yaml

5. Apply directly to Kubernetes (optional)

   ./helmlet --template template.yaml --value values.yaml | kubectl apply -f -

Command Line Options

Flag	Description	Example
--template	Template file(s) to process (can be specified multiple times)	--template deployment.yaml
--template-dir	Directory containing template files	--template-dir k8s-templates/
--value	Values file(s) to load (can be specified multiple times)	--value values.yaml
--set	Set values on the command line	--set image.tag=v1.2.3,replicas=3
--set-separator	Separator for values in --set (default is comma)	--set-separator ';'
--output	Write output to file (for single templates)	--output rendered.yaml
--output-dir	Directory to write output files (for multiple templates)	--output-dir rendered/
--delimiter	Custom template delimiters	--delimiter '<%,%>'
--strict	If true, fail when template uses missing keys	--strict

📚 Examples

Basic Usage

# Simple template rendering with command line values
./helmlet --template template.yaml --set key1=value1,key2=value2

# Render with values from file
./helmlet --template template.yaml --value values.yaml

# Output to file instead of stdout
./helmlet --template template.yaml --value values.yaml --output rendered.yaml

Advanced Usage

# Layer multiple values files (values from later files override earlier ones)
./helmlet --template template.yaml --value common.yaml --value dev.yaml --value app.yaml

# Process an entire directory of templates
./helmlet --template-dir templates/ --value values.yaml --output-dir rendered/

# Process multiple specific templates
./helmlet --template template1.yaml --template template2.yaml --value values.yaml --output-dir rendered/

# Use quoted values to include commas in values
./helmlet --template template.yaml --set 'key1="value1,has,commas"'

# Use a different separator to avoid needing quotes for values containing commas
./helmlet --template template.yaml --set 'key1=value1,with,commas;key2=value2' --set-separator ';'

# Use custom delimiters to avoid conflicts
./helmlet --template template.yaml --value values.yaml --delimiter '<%,%>'

# Enable strict mode to fail on missing values
./helmlet --template template.yaml --value values.yaml --strict

🛠️ Integration with Kubernetes

# Render template and pipe directly to kubectl
./helmlet --template deployment.yaml --value values.yaml | kubectl apply -f -

# Process templates and save for later use
./helmlet --template-dir k8s-templates/ --value values.yaml --output-dir k8s-manifests/
kubectl apply -f k8s-manifests/

🌟 Features

Core Features

• Templating Engine: Go templates with custom functions similar to Helm
• Multiple Template Processing: Process individual files or entire directories
• Value Management:
  • Layer multiple value files (later files override earlier ones)
  • Set individual values via command line
  • Support for nested values with dot notation (e.g., app.config.port=8080)
• Output Options:
  • Direct to stdout for piping to kubectl or other tools
  • Single output file for individual templates
  • Output directory for batch processing multiple templates

Template Functions Supported

• default: Provide default values when variables are undefined
• quote: Properly quote string values
• indent: Control indentation for multiline strings
• tpl: Dynamically process strings as templates
• FilesGet: Include external files within templates

Special Features

• Strict Mode: Optional enforcement of required template variables
• Custom Delimiters: Change template delimiters to avoid conflicts with target formats
• UTF-8 Conversion: Automatically detects and converts non-UTF8 files

🤝 Contributing

We welcome contributions! Please feel free to submit a pull request (PR) or open an issue on GitHub.