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helm-charts-template-guide.md

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Helm Templates

Helm Charts built-in-objects

  • Release: This object describes the release itself. It has several objects inside of it:

    • Release.Name: The release name
    • Release.Namespace: The namespace to be released into (if the manifest doesn’t override)
    • Release.IsUpgrade: This is set to true if the current operation is an upgrade or rollback.
    • Release.IsInstall: This is set to true if the current operation is an install.
    • Release.Revision: The revision number for this release. On install, this is 1, and it is incremented with each upgrade and rollback.
    • Release.Service: The service that is rendering the present template. On Helm, this is always Helm.

  • Values: Values passed into the template from the values.yaml file and from user-supplied files. By default, Values is empty.

  • Chart: The contents of the Chart.yaml file. Any data in Chart.yaml will be accessible here. For example {{ .Chart.Name }}-{{ .Chart.Version }} will print out the mychart-0.1.0.

  • The available fields are listed in the Charts Guide

  • Files: This provides access to all non-special files in a chart. While you cannot use it to access templates, you can use it to access other files in the chart. See the section Accessing Files for more.

    • Files.Get : is a function for getting a file by name (.Files.Get config.ini)
    • Files.GetBytes : is a function for getting the contents of a file as an array of bytes instead of as a string. This is useful for things like images.
    • Files.Glob : is a function that returns a list of files whose names match the given shell glob pattern.
    • Files.Lines : is a function that reads a file line-by-line. This is useful for iterating over each line in a file.
    • Files.AsSecrets : is a function that returns the file bodies as Base 64 encoded strings.
    • Files.AsConfig : is a function that returns file bodies as a YAML map.

  • Capabilities: This provides information about what capabilities the Kubernetes cluster supports.

    • Capabilities.APIVersions : is a set of versions.
    • Capabilities.APIVersions.Has $version indicates whether a version (e.g., batch/v1) or resource (e.g., apps/v1/Deployment) is available on the cluster.
    • Capabilities.KubeVersion and Capabilities.KubeVersion.Version is the Kubernetes version.
    • Capabilities.KubeVersion.Major is the Kubernetes major version.
    • Capabilities.KubeVersion.Minor is the Kubernetes minor version.

  • Template: Contains information about the current template that is being executed

    • Name: A namespaced file path to the current template (e.g. mychart/templates/mytemplate.yaml)
    • BasePath: The namespaced path to the templates directory of the current chart (e.g. mychart/templates).

helm : lookup function

The lookup function can be used to lookup resources in a running cluster

helm : Qoute function

When injecting strings from the .values,object into the template,we ought to quote these strings, we can do that by calling the quote function in the template directive.

helm : Flow-Control

  • Helm's template language provides the following control structures:

    • if/else for creating conditional blocks
    • with to specify a scope
    • range, which provides a "for each"-style loop