Helm Component

Helm is a popular packaging technology for Kubernetes applications. We do provide our own opinionated way how to deploy helm components.

Component Conventions

If component follows the conventions below, then hubctl will know how to deploy it.

Helm Detection

When you want to use helm deployment add the following definition to the hub-component.yaml

requires:
- kubernetes
- helm

and place one one of the following files in the component directory: values.yaml, values.yaml.template or values.yaml.gotemplate

Then hubctl will be able detect this component as helm component and call provisioning script: helm-component-deploy .

Input parameters

As every script, helm deployment scripts has been controlled via set off well-known environment variables. These variables should be defined in parameters section of hub-component.yaml. List of expected environment variables

Variable	Description	Required
`DOMAIN_NAME`	FQDN of a stack. We use this parameter as a natural id of the deployment (defaults to implicit variable `HUB_DOMAIN_NAME`). Usage of this variables requires user to define a parameter `dns.domain` in `hub-component.yaml`. Yet we advice to use instead an implicit variable `HUB_DOMAIN_NAME` instead
`COMPONENT_NAME`	Corresponds to parameter `hub.componentName` parameter, however can be overriden in `hub-component.yaml`. Hub will use this variable as a helm release name	x
`NAMESPACE`	Target kubernetes namespace	x
`HELM_CHART`	This can have multiple values, that corresponds to the helm chart location. Corresponds to the helm chart tar url, tarball, directory or a chart name in the repository	x
`HELM_REPO`	Instructs hubctl to download helm chart from the helm repository
`HELM_CHART_VERSION`	Addes a version constraint to the helm chart install. This variable works in conjunction with `HELM_REPO`
`HELM_CHART_USERNAME` and `HELM_CHART_PASSWORD`	Username and password for helm chart repository basic auth
`CHART_VALUES_FILE`	Instructs hubctl that it must use concrete values file inside of the helm chart as the base and only override with parameters from `values.yaml` in the component root directory. Alternatively if this variable has prefix `http` or `https` then the file. Additional values files can be referenced by adding a whitespace (or new line) separated reference
`CRD`	URL or local path to the CRD file (if not located in `<component root>/crds` directory)
`HELM_OPTS`	Helm command arguments, defautls to `--create-namespace --wait`

Environment variable: `HELM_CHART`

Helm chart which user wants to deploy can be resolved via variable HELM_CHART. This variable corresponds to the following value:

Path to the local directory with the helm chart (relative to the <component root> or <component root>/charts directory)
Path to the local directory with the helm chart (relative to the <component root> or <component root>/charts directory )
Name of the helm chart in the helm repository (requires user to define: HELM_REPO and HELM_CHART_VERSION)

Deployment hooks

User can define pre and post deployment

pre-deploy or pre-deploy.sh to trigger action before helm install
post-deploy or post-deploy.sh to trigter action after successful helm install
pre-undeploy or pre-undeploy.sh to trigger action before helm delete
post-undeploy or post-undeploy.sh to trigger action after helm successful delete

Note: pre and post deployment scripts should have execution rights

Custom Resources

We do advise not to deploy CRD with the helm chart. Because component undeploy (and helm delete correspondingly) will also delete CRDs. Deletion of CRD will also delete custom resources that may have been deployed by the user after this component has been deployed. Instead we advise to put your CRDs in to the <component root>/crds directory. In this case, CRDs will be managed separately from the helm chart

CRDs will be deploymed before the helm chart
CRDs will not be deleted after component will be undeployed. Which means you can redeploy the component without dropping user custom resources

Examples

Nginx web server example. This is an example of a hub-component.yaml that will install a helm chart without any modifications. Complete code for nginx component can be found here

---
version: 1
kind: component
requires:
  - kubernetes
  - helm
provides:
  - nginx
  - ingress
parameters:
  - name: ingress.namespace
    value: ingress
    env: NAMESPACE
  - name: ingress.class
    value: nginx
  - name: helm
    parameters:
      - name: chart
        value: nginx-ingress
        env: HELM_CHART
      - name: repo
        value: https://helm.nginx.com/stable
        env: HELM_REPO
      - name: version
        value: 0.13.2
        env: HELM_CHART_VERSION
templates:
  files:
    - values.yaml.template

Note: helm chart parameters values must be defined in the values.yaml.template alternatively you can run values.yaml.gotemplate file