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

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# 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/<train>/<chart name>/
charts/ # Directory containing dependency charts
Chart.yaml # Required Helm chart information file
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
```
```
charts/<train>/<chart name>/
app-readme.md # TrueNAS SCALE Specific: Readme file for display in TrueNAS SCALE UI
questions.yaml # TrueNAS SCALE Specific: File containing questions for TrueNAS SCALE UI
ix_values.yaml # Hidden configuration values when installing using TrueNAS SCALE
```
*See the upstream Helm chart [developer reference](https://helm.sh/docs/chart_template_guide/) 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/<train>/<chart name>/SCALE/item.yaml
categories:
- generic
icon_url: "http://ix_url"
```
After that create `app-readme.md` file.
```
$ cat charts/<train>/<chart name>/SCALE/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](https://wiki.truecharts.org/development/questions-yaml/)_