TrueChartsClone/docs/development/app development/chart-structure.md

TrueNAS SCALE Chart Structure

A TrueNAS SCALE chart repository differs slightly in directory structure from upstream repos in that it includes an app version directory.

A TrueNAS SCALE chart also has three additional files an app-readme.md file that provides a high level overview display in the TrueNAS SCALE UI and a questions.yaml file defining questions to prompt the user with and an item.yaml file outlining item specific details.

There are 2 directories charts and test, each representing a train. Chart releases created from catalog items in a specific train cannot be moved to another train. Currently only the charts train can be used inside the UI.

charts/ix-chart/<chart version>/
  app-readme.md            # TrueNAS SCALE Specific: Readme file for display in TrueNAS SCALE UI
  charts/                  # Directory containing dependency charts
  Chart.yaml               # Required Helm chart information file
  questions.yaml           # TrueNAS SCALE Specific: File containing questions for TrueNAS SCALE UI
  README.md                # Optional: Helm Readme file (will be rendered in TrueNAS SCALE UI as well)
  templates/               # A directory of templates that, when combined with values.yml will generate K8s YAML
  values.yaml              # The default configuration values for this chart

See the upstream Helm chart developer reference for a complete walk through of developing charts.

To convert an upstream chart to take advantage of TrueNAS SCALE enhanced UX, first create an item.yaml file. This file among other catalog item information provides a list of categories that this chart fits into. This helps users navigate and filtering when browsing the catalog UI.

$ cat charts/ix-chart/item.yaml
categories:
  - generic
icon_url: "http://ix_url"

After that create app-readme.md file.

$ cat charts/ix-chart/<chart version>/app-readme.md

iX-chart is a chart designed to let user deploy a docker image in a TrueNAS SCALE kubernetes cluster.
It provides a mechanism to specify workload type, add external host interfaces in the pods, configure volumes and allocate host resources to the workload.

Then add a questions.yaml file to prompt the user for something.

groups:
  - name: "Container Images"
    description: "Image to be used for container"
questions:
  - variable: image
    description: "Docker Image Details"
    group: "Container Images"
    schema:
      type: dict
      required: true
      attrs:
        - variable: repository
          description: "Docker image repository"
          label: "Image repository"
          schema:
            type: string
            required: true
        - variable: tag
          description: "Tag to use for specified image"
          label: "Image Tag"
          schema:
            type: string
            default: "latest"
        - variable: pullPolicy
          description: "Docker Image Pull Policy"
          label: "Image Pull Policy"
          schema:
            type: string
            default: "IfNotPresent"
            enum:
              - value: "IfNotPresent"
                description: "Only pull image if not present on host"
              - value: "Always"
                description: "Always pull image even if present on host"
              - value: "Never"
                description: "Never pull image even if it's not present on host"

The above will prompt the user with 2 text fields and a dropdown in the UI getting details for image configuration in a helm chart. More information about questions.yaml is available here