Helm Templates

External

• The Chart Template Developer’s Guide https://helm.sh/docs/chart_template_guide/#the-chart-template-developer-s-guide

Internal

• Helm Concepts
• helm install

Overview

Templates are files living under a chart's templates/ directory. They are written in YAML with Helm templates extensions. Upon processing by Helm, they become Kubernetes manifest files. Helm template extensions are written in the Help template language, which is based on Go templates.

The templates/ Directory

The 'templates' directory contains templates that, after combination with values, will the Kubernetes manifests. When Tiller evaluates a chart, it will send all of the files in the directory through the template rendering engine, then collect the results and send them to to Kubernetes.

Template names do not follow a rigid naming pattern. It is, however, recommended to use the suffix .yaml for YAML files and .tpl for helpers.

It also contains the following files:

• NOTES.txt
• _helpers.tpl

Files whose names start with "_" or "." will be ignored. - Really? helm install complained about _pod.yaml.

Template Directives

A template directive is enclosed in {{ and }} blocks, and it is recommended to pad the directive with space at its left and right.

Simple Replacement

The simplest directive is a value, which is a namespaced object, where each dot (.) separates each namespaced element. A leading dot indicates that we start with the top-most namespace for the scope.

kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap

Built-in Objects

Built-in Objects

Chart

Exposes all contents of Chart.yaml. An existing field is available as (note leading dot) .Chart.<UpperCasedFirstLetterFieldName>.

Example:

{{ .Chart.Name }}
{{ .Chart.Version }}

Release

Release.Name

Exposes the release name:

{{ .Release.Name }}

Release.Revision

Exposes the release revision:

{{ .Release.Revision }}

Release.Time

Exposes the time of the release:

{{ .Release.Time }}

Release.Namespace

Exposes the namespace to be released info, if the manifest does not override:

{{ .Release.Namespace }}

Release.IsUpgrade

This is set to true if the current operation is an upgrade or rollback.

{{ .Release.IsUpgrade }}

Release.IsInstall

This is set to true if the current operation is an install.

{{ .Release.IsInstall }}

Release.Service

Exposes the releasing service - always Tiller

TODO

Template Comments

# This is a comment

{{- /*
This is another comment
*/ -}}

TODO

• https://helm.sh/docs/chart_template_guide/#the-chart-template-developer-s-guide
• https://helm.sh/docs/chart_best_practices/#templates
• https://helm.sh/docs/developing_charts/#templates-and-values
• https://helm.sh/docs/developing_charts/#know-your-template-functions
• https://helm.sh/docs/developing_charts/#quote-strings-don-t-quote-integers
• https://helm.sh/docs/developing_charts/#using-the-include-function
• https://helm.sh/docs/developing_charts/#using-the-required-function
• https://helm.sh/docs/developing_charts/#using-the-tpl-function
• https://helm.sh/docs/developing_charts/#creating-image-pull-secrets
• https://helm.sh/docs/developing_charts/#automatically-roll-deployments-when-configmaps-or-secrets-change
• https://helm.sh/docs/developing_charts/#tell-tiller-not-to-delete-a-resource
• https://helm.sh/docs/developing_charts/#using-partials-and-template-includes
• https://helm.sh/docs/chart_best_practices/#pods-and-podtemplates
• https://helm.sh/docs/chart_best_practices/#images
• https://helm.sh/docs/chart_best_practices/#imagepullpolicy
• https://helm.sh/docs/chart_best_practices/#podtemplates-should-declare-selectors