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Defining Installation Order for Helm Charts

This topic describes how to use the weight property in HelmChart custom resources to define the installation order for Helm charts. For more information about installing Helm charts with Replicated KOTS, see About Distributing Helm Charts with KOTS.

About Installation Weight​

You can add a weight property to the HelmChart custom resource manifest file to define the order in which Helm installs the charts. For more information, see weight in HelmChart v2.

This is useful if you have multiple HelmChart custom resources in your application, and it is important that the resources referenced in one or more Helm charts are deployed before one or more other Helm charts.

Assigning a weight also helps you avoid relying on Helm dependencies and subcharts to define a chart installation order in Replicated KOTS. This is particularly useful when you include hooks in your Helm charts, as Helm waits for certain hooks to complete before continuing. For more information about how KOTS handles dependencies and hooks for Helm charts, see Subcharts and Dependencies and Hooks below.

KOTS directs Helm to install the Helm charts in your application based on the value of weight in ascending order, deploying the chart with the lowest weight first. For example, a chart with a weight of -1 deploys before a chart with a weight of 0.

The value for the weight property can be any negative or positive integer or 0. By default, when you do not provide a weight for a Helm chart, the weight is 0.

Limitations​

The weight field in the HelmChart custom resource has the following limitations:

  • The weight field is not supported for Helm charts installed with HelmChart custom resources that have apiVersion: kots.io/v1beta1 and useHelmInstall: false.

  • The following hooks are not supported and are ignored if they are present:

    • test
    • pre-rollback
    • post-rollback

  • Hook weights below -9999 are not supported. All hook weights must be set to a value above -9999 to ensure the Replicated image pull secret is deployed before any resources are pulled.

Subcharts and Dependencies​

When you add a weight property to HelmChart custom resources in your application, KOTS instructs Helm to install any dependencies, including subcharts, along with the parent chart.

For example, if you have two Helm charts in your application, one with a weight of -1 and one with a weight of 0, then Helm installs the chart with a weight of -1 first, including any subcharts and dependencies listed in the dependencies field for that chart.

If you do not add a weight to Helm charts in your application, you can still use dependencies and subcharts to define installation order constraints during application deployment.

For more information about using Helm dependencies, see Chart Dependencies in the Helm documentation.

Hooks​

Helm hooks enable more control over when Helm installs the resources in your Helm charts. This is useful if you want to bundle actions as part of a release. For example, you can build in a database backup as part of the upgrade process while ensuring that the backup occurs prior to upgrading the rest of the resources.

KOTS supports using some Helm hooks with Helm charts. If you use hooks in your Helm charts, you can use the weight property to further manage the installation order of resources. For example, if you include a pre-install hook in Helm chart A that requires a resource from Helm chart B, you can add a lower weight to chart B to ensure that Replicated KOTS directs Helm to install chart B before chart A.

The following hooks are supported:

  • pre-install: Executes after resources are rendered but before any resources are installed.
  • post-install: Executes after resources are installed.
  • pre-upgrade: Executes after resources are rendered but before any resources are upgraded.
  • post-upgrade: Executes after resources are upgraded.
  • pre-delete: Executes before any resources are deleted.
  • post-delete: Executes after resources are deleted.

The following hooks are not supported and are ignored if they are present:

  • test
  • pre-rollback
  • post-rollback

For more information about Helm hooks and weights, see the Chart Hooks in the Helm documentation.