Helm Templates: Difference between revisions

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<font color=darkgray>Files whose names start with "_" or "." will be ignored. - Really? helm install complained about _pod.yaml.</font>
<font color=darkgray>Files whose names start with "_" or "." will be ignored. - Really? helm install complained about _pod.yaml.</font>
=Template Comments=
# This is a comment
{{- /*
This is another comment
*/ -}}


=Template Directives=
=Template Directives=

Revision as of 04:13, 29 August 2019

External

Internal

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:

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

Template Comments

# This is a comment

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

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

Scopes

Template Objects

Objects are passed into a template from the template engine. The template directives can create new objects and pass them around. There are also built-in objects, which are made available by default.

Objects can be simple - have just one value -, or they can contain other objects or functions. For example the "Release" built-in object contains several other objects (like "Release.Name"). The "Files" object contains functions.

Built-in Objects

Built-in Objects

The built-in values always begin with a capital letter, based on Go's naming convention. For a fully working examples of built-in objects replacement see:

https://github.com/ovidiuf/playground/tree/master/helm/bactrosaurus

Chart

This object contains value passed into the template from the Chart.yaml file. An existing field is available as (note leading dot) .Chart.<UpperCasedFirstLetterFieldName>. It is important to capitalize the first letter of the field name, otherwise the directive evaluation fails.

Example: 

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

Values

This object contains values passed into template from the values.yaml file and from other user sources. An existing field is available as (note leading dot) .Values.<fieldName>. Unlike in Chart's case, the fields are allowed to keep their original capitalization. For example, a value declared as such in values.yaml: 

size: 10

can be references in a template as: 

kind: ConfigMap
...
data:
  size: {{ .Values.size }}

Values can contain structured content: 

characteristics:
  size: 10
  shape: "large"

can be referenced in template as: 

kind: ConfigMap
...
data:
  size: {{ .Values.characteristics.size }}
  shape: {{ .Values.characteristics.shape }}

While structuring data this way is possible, the recommendation is to keep values trees shallow, favoring flatness.

Release

This object describes the release itself.

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

Files

The object provide access to all non-special files in the chart. It cannot be used to access templates. The access is provided via several functions:

Files.Get

{{ .Files.Get <file-name> }}

Files.GetBytes

Capabilities

Provides information about the capabilities of the Kubernetes cluster: 

{{ .Capabilities.APIVersions }}
{{ .Capabilities.APIVersions.Has }}
{{ .Capabilities.KubeVersion }}
{{ .Capabilities.KubeVersion.Major|
 Minor|GitVersion|GitCommit|GitTreeState|BuildDate|GoVersion|Compiler|Platform}}
{{ .Capabilities.TillerVersion }}

Template

Contains information about the current template that is being executed: 

{{ .Template.Name }}
{{ .Template.BasePath }}

Template Functions

Template Functions and Pipelines

Template Pipelines

Pipelines

TODO

TODO

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