Helm Generator

A resource generator for Helm charts

Sometimes it is desired to write a component operator (using component-operator-runtime) for some cluster component, which already has a productive Helm chart. Then it can make sense to use the HelmGenerator implementation of the Generator interface included in this module:

package helm

func NewHelmGenerator(
  fsys                  fs.FS,
  chartPath             string,
  clnt                client.Client,
) (*HelmGenerator, error)

Here:

  • fsys must be an implementation of fs.FS, such as embed.FS; or it can be passed as nil; then, all file operations will be executed on the current OS filesystem.
  • chartPath is the directory containing the used Helm chart; if fsys was provided, this has to be a relative path; otherwise, it will be interpreted with respect to the OS filesystem (as an absolute path, or relative to the current working directory of the controller).
  • clnt should be a client for the local cluster (i.e. the cluster where the component object exists).

It should be noted that HelmGenerator does not use the Helm SDK; instead it tries to emulate the Helm behavior as good as possible. A few differences and restrictions arise from this:

  • Not all Helm template functions are supported. To be exact, toToml is not supported; all other functions should be supported, but may behave more strictly in error situtations.
  • Not all builtin variables are supported; the following restrictions apply:
    • for the .Release builtin, only .Release.Namespace, .Release.Name, .Release.Service, .Release.IsInstall, .Release.IsUpgrade are supported; note that - since this framework does not really distinguish between installations and upgrades - Release.IsInstall is always set to true, and Release.IsUpgrade is always set to false
    • for the .Chart builtin, only .Chart.Name, .Chart.Version, .Chart.Type, .Chart.AppVersion, .Chart.Dependencies are supported
    • for the .Capabilities builtin, only .Capabilities.KubeVersion and .Capabilities.APIVersions are supported
    • the .Template builtin is fully supported
    • the .Files builtin is supported but does not return any of the paths reserved by Helm (such as Chart.yaml, templates/ and so on)
  • Regarding hooks, pre-delete and post-delete hooks are not allowed; test and rollback hooks are ignored, and pre-install, post-install, pre-upgrade, post-upgrade hooks might be handled in a sligthly different way; hook weights will be handled in a compatible way; hook deletion policy hook-failed is not allowed, but before-hook-creation and hook-succeeded should work as expected.
  • The .helmignore file is currently not evaluated; in particular, files can be accessed through .Files altough they are listed in .helmignore.