getting started with ytt: a better way to template yaml

ytt is a YAML templating tool that helps you customize and generate YAML files dynamically. It provides a more powerful and expressive way to work with YAML than standard templating tools like Helm templates. With ytt, you can leverage data values, conditional logic, loops, and more to create modular and reusable YAML configurations.

Here’s why ytt might be the right tool for your next project:

1. Structured Data Management: ytt treats YAML as structured data, allowing for more complex and reliable transformations.
2. Reusable Templates: Create reusable templates that can be shared across projects or teams.
3. Powerful Scripting: Use ytt’s embedded scripting language, Starlark, to introduce logic, loops, and conditionals in your YAML.
4. Separation of Data and Templates: Keep your data values separate from your templates, making your configurations more maintainable and easier to update.

Before getting started with ytt, ensure you have the following:

• ytt Installed: You can install ytt by downloading it from the Carvel GitHub repository or using a package manager like Homebrew:

  brew install ytt

• Basic Knowledge of YAML: Familiarity with YAML syntax is essential to make the most of ytt.

If you haven’t installed ytt yet, you can easily do so with Homebrew (on macOS) or by downloading the binary from the Carvel GitHub page.

brew install ytt

Or download directly:

wget https://github.com/carvel-dev/ytt/releases/download/v0.38.0/ytt-linux-amd64
chmod +x ytt-linux-amd64
sudo mv ytt-linux-amd64 /usr/local/bin/ytt

Let’s start by creating a basic YAML file and template it using ytt. Assume you have a simple Kubernetes Deployment YAML:

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: simple-deployment
spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: simple-app
    spec:
      containers:
      - name: simple-container
        image: simple-image:1.0.0

Now, let’s convert this into a ytt template that can dynamically change the number of replicas and the image version.

Create a values.yaml file to store your variable data:

values.yaml

#@data/values
---
replicas: 3
image_version: "1.0.0"

Modify the deployment.yaml to include ytt templating directives:

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: simple-deployment
spec:
  replicas: #@ data.values.replicas
  template:
    metadata:
      labels:
        app: simple-app
    spec:
      containers:
      - name: simple-container
        image: simple-image:#@ data.values.image_version

Now, you can use ytt to render your templated YAML:

ytt -f deployment.yaml -f values.yaml

The output will be a fully rendered YAML file with the replicas and image version substituted from your values.yaml.

ytt allows you to add complex logic, conditionals, and loops. You can extend your templates with more advanced features using Starlark scripting to meet the specific needs of your infrastructure.

ytt is a powerful tool that can significantly improve how you manage and template YAML files. By separating your data from your templates, introducing conditional logic, and reusing components, ytt makes it easier to maintain and scale your YAML configurations across projects. Whether you’re managing Kubernetes manifests or any other YAML-based configurations, ytt is a tool that should be in every DevOps engineer’s toolkit.

Give ytt a try in your next project, and experience the benefits of structured YAML templating!