Merging helm input values using kustomize

Helm is a popular package manager for Kubernetes applications.It bundles Kubernetes manifests for a given application to a set used for deployments. Furthermore, helm providesdependency management as well as a templating engine (go templates with sprig-functions).

Kustomize is a configuration management tool that is used to merge and patch Kubernetes manifests.

Using kustomize to merge helm input values

When combining helm and kustomize (e.g. to patch helm output manifests) it is a likely scenario that one has the need to reproduceHelms merge logic regarding multiple input files. This is useful to o e.g. separate basic settings from stage-dependent settings.A usual strategy with kustomize is to use bases and overlays.

To apply this to the values of a helm chart one has to use the file-based HelmChartInflationGenerator, it has the format of a k8s custom resource (but is not one):

apiVersion: builtin
kind: HelmChartInflationGenerator
metadata:
  name: just-for-kustomize-matching
releaseName: helm-release-name
name: chart-name
version: chart-version
repo: repo-url
valuesInline: {}

This then has to be combined it with the transformed transformers pattern (also works for generators, "everything is a transformer").So the file structure would look like this:

The two values.yaml have to be in the form of the builtin/HelmChartInflationGenerator described above. Now follows the content of the relevant yaml files:

# base/helm/kustomization.yaml
# just include the raw base values yaml
resources:
  - values.yaml
  
# dev/helm/kustomization.yaml
# merge the HelmChartInflationGenerator generator input using patch strategic merge
bases:
- ../../base/helm/kustomization.yaml

patchStrategicMerge:
  - values.yaml

# dev/kustomization.yaml
# use output of the helm subfolder kustomize call as generator input
generators:
  - helm