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kubevela/docs/en/helm/component.md
Lei Zhang (Harry) d8eb7d687c Add user docs (#1472)
2021-04-13 15:20:39 +08:00

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---
title: How-to
---
In this section, it will introduce how to declare Helm charts as app components via `ComponentDefinition`.
> Before reading this part, please make sure you've learned [the definition and template concepts](../platform-engineers/definition-and-templates).
## Prerequisite
* Make sure you have enabled Helm support in the [installation guide](/docs/install).
## Declare `ComponentDefinition`
Here is an example `ComponentDefinition` about how to use Helm as schematic module.
```yaml
apiVersion: core.oam.dev/v1beta1
kind: ComponentDefinition
metadata:
name: webapp-chart
annotations:
definition.oam.dev/description: helm chart for webapp
spec:
workload:
definition:
apiVersion: apps/v1
kind: Deployment
schematic:
helm:
release:
chart:
spec:
chart: "podinfo"
version: "5.1.4"
repository:
url: "http://oam.dev/catalog/"
```
In detail:
- `.spec.workload` is required to indicate the workload type of this Helm based component. Please also check for [Known Limitations](/docs/helm/known-issues?id=workload-type-indicator) if you have multiple workloads packaged in one chart.
- `.spec.schematic.helm` contains information of Helm `release` and `repository` which leverages `fluxcd/flux2`.
- i.e. the pec of `release` aligns with [`HelmReleaseSpec`](https://github.com/fluxcd/helm-controller/blob/main/docs/api/helmrelease.md) and spec of `repository` aligns with [`HelmRepositorySpec`](https://github.com/fluxcd/source-controller/blob/main/docs/api/source.md#source.toolkit.fluxcd.io/v1beta1.HelmRepository).
## Declare an `Application`
Here is an example `Application`.
```yaml
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: myapp
namespace: default
spec:
components:
- name: demo-podinfo
type: webapp-chart
properties:
image:
tag: "5.1.2"
```
The component `properties` is exactly the [overlay values](https://github.com/captainroy-hy/podinfo/blob/master/charts/podinfo/values.yaml) of the Helm chart.
Deploy the application and after several minutes (it may take time to fetch Helm chart), you can check the Helm release is installed.
```shell
$ helm ls -A
myapp-demo-podinfo default 1 2021-03-05 02:02:18.692317102 +0000 UTC deployed podinfo-5.1.4 5.1.4
```
Check the workload defined in the chart has been created successfully.
```shell
$ kubectl get deploy
NAME READY UP-TO-DATE AVAILABLE AGE
myapp-demo-podinfo 1/1 1 1 66m
```
Check the values (`image.tag = 5.1.2`) from application's `properties` are assigned to the chart.
```shell
$ kubectl get deployment myapp-demo-podinfo -o json | jq '.spec.template.spec.containers[0].image'
"ghcr.io/stefanprodan/podinfo:5.1.2"
```
### Generate Form from Helm Based Components
KubeVela will automatically generate OpenAPI v3 JSON schema based on [`values.schema.json`](https://helm.sh/docs/topics/charts/#schema-files) in the Helm chart, and store it in a `ConfigMap` in the same `namespace` with the definition object. Furthermore, if `values.schema.json` is not provided by the chart author, KubeVela will generate OpenAPI v3 JSON schema based on its `values.yaml` file automatically.
Please check the [Generate Forms from Definitions](/docs/platform-engineers/openapi-v3-json-schema) guide for more detail of using this schema to render GUI forms.