Rancher’s catalog service requires any custom catalogs to be structured in a specific format for the catalog service to be able to leverage it in Rancher.

Chart Types

Rancher supports two different types of charts:

  • Helm Charts

    Native Helm charts include an application along with other software required to run it. When deploying native Helm charts, you’ll learn the chart’s parameters and then configure them using Answers, which are sets of key value pairs.

    The Helm Stable and Helm Incubators are populated with native Helm charts. However, you can also use native Helm charts in Custom catalogs (although we recommend Rancher Charts).

  • Rancher Charts

    Rancher charts mirror native helm charts, although they add two files that enhance user experience: app-readme.md and questions.yaml. Read more about them in Rancher Chart Additional Files.

    Advantages of Rancher charts include:

    • Enhanced Revision Tracking

      While Helm supports versioned deployments, Rancher adds tracking and revision history to display changes between different versions of the chart.

    • Streamlined Application Launch

      Rancher charts add simplified chart descriptions and configuration forms to make catalog application deployment easy. Rancher users need not read through the entire list of Helm variables to understand how to launch an application.

    • Application Resource Management

      Rancher tracks all the resources created by a specific application. Users can easily navigate to and troubleshoot on a page listing all the workload objects used to power an application.

Chart Directory Structure

The following table demonstrates the directory structure for a chart, which can be found in a chart directory: charts/<APPLICATION>/<APP_VERSION>/. This information is helpful when customizing charts for a custom catalog. Files denoted with Rancher Specific are specific to Rancher charts, but are optional for chart customization.

charts/<APPLICATION>/<APP_VERSION>/
|--charts/           # Directory containing dependency charts.
|--templates/        # Directory containing templates that, when combined with values.yml, generates Kubernetes YAML.
|--app-readme.md     # Text displayed in the charts header within the Rancher UI.*
|--Chart.yml         # Required Helm chart information file.
|--questions.yml     # Form questions displayed within the Rancher UI. Questions display in Configuration Options.*
|--README.md         # Optional: Helm Readme file displayed within Rancher UI. This text displays in Detailed Descriptions.
|--requirements.yml  # Optional: YAML file listing dependencies for the chart.
|--values.yml        # Default configuration values for the chart.

Rancher Chart Additional Files

Before you create your own custom catalog, you should have a basic understanding about how a Rancher chart differs from a native Helm chart. Rancher charts differ slightly from Helm charts in their directory structures. Rancher charts include two files that Helm charts do not.

  • app-readme.md

    A file that provides descriptive text in the chart’s UI header. The following image displays the difference between a Rancher chart (which includes app-readme.md) and a native Helm chart (which does not).

    Rancher Chart with app-readme.md (left) vs. Helm Chart without (right)

    app-readme.md

  • questions.yml

    A file that contains questions for a form. These form questions simplify deployment of a chart. Without it, you must configure the deployment using key value pairs, which is more difficult. The following image displays the difference between a Rancher chart (which includes questions.yml) and a native Helm chart (which does not).

    Rancher Chart with questions.yml (left) vs. Helm Chart without (right)

    questions.yml

Questions.yml

Inside the questions.yml, most of the content will be around the questions to ask the end user, but there are some additional fields that can be set in this file.

Min/Max Rancher versions

Available as of v2.3.0

For each chart, you can add the minimum and/or maximum Rancher version, which determines whether or not this chart is available to be deployed from Rancher.

Note: Even though Rancher release versions are prefixed with a v, there is no prefix for the release version when using this option.

rancher_min_version: 2.3.0
rancher_max_version: 2.3.99

Question Variable Reference

This reference contains variables that you can use in questions.yml nested under questions:.

Variable Type Required Description
variable string true Define the variable name specified in the values.yml file, using foo.bar for nested objects.
label string true Define the UI label.
description string false Specify the description of the variable.
type string false Default to string if not specified (current supported types are string, boolean, int, enum, password, storageclass and hostname).
required bool false Define if the variable is required or not (true | false)
default string false Specify the default value.
group string false Group questions by input value.
min_length int false Min character length.
max_length int false Max character length.
min int false Min integer length.
max int false Max integer length.
options []string false Specify the options when the variable type is enum, for example: options:
- “ClusterIP”
- “NodePort”
- “LoadBalancer”
valid_chars string false Regular expression for input chars validation.
invalid_chars string false Regular expression for invalid input chars validation.
subquestions []subquestion false Add an array of subquestions.
show_if string false Show current variable if conditional variable is true. For example show_if: "serviceType=Nodeport"
show_subquestion_if string false Show subquestions if is true or equal to one of the options. for example show_subquestion_if: "true"

Note: subquestions[] cannot contain subquestions or show_subquestions_if keys, but all other keys in the above table are supported.

Example Custom Chart Creation

You can fill your custom catalogs with either Helm Charts or Rancher Charts, although we recommend Rancher Charts due to their enhanced user experience.

Note: For a complete walkthrough of developing charts, see the upstream Helm chart developer reference.

  1. Within the GitHub repo that you’re using as your custom catalog, create a directory structure that mirrors the structure listed in Chart Directory Structure.

    Rancher requires this directory structure, although app-readme.md and questions.yml are optional.

    Tip:

  2. Recommended: Create an app-readme.md file.

    Use this file to create custom text for your chart’s header in the Rancher UI. You can use this text to notify users that the chart is customized for your environment or provide special instruction on how to use it.

    Example:

    $ cat ./app-readme.md

# Wordpress ROCKS!

  3. Recommended: Create a questions.yml file.

    This file creates a form for users to specify deployment parameters when they deploy the custom chart. Without this file, users must specify the parameters manually using key value pairs, which isn’t user-friendly.

    The example below creates a form that prompts users for persistent volume size and a storage class.

    For a list of variables you can use when creating a questions.yml file, see Question Variable Reference.

        categories:
    - Blog
    - CMS
    questions:
    - variable: persistence.enabled
    default: "false"
    description: "Enable persistent volume for WordPress"
    type: boolean
    required: true
    label: WordPress Persistent Volume Enabled
    show_subquestion_if: true
    group: "WordPress Settings"
    subquestions:
    - variable: persistence.size
        default: "10Gi"
        description: "WordPress Persistent Volume Size"
        type: string
        label: WordPress Volume Size
    - variable: persistence.storageClass
        default: ""
        description: "If undefined or null, uses the default StorageClass. Default to null"
        type: storageclass
        label: Default StorageClass for WordPress

  4. Check the customized chart into your GitHub repo.

Result: Your custom chart is added to the repo. Your Rancher Server will replicate the chart within a few minutes.