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Mutations

Mutations in kgenlib

Introduction to Mutations

In kgenlib, "Mutations" are tools that let you modify the objects generated based on certain criteria. They provide more granular control over the generation process, allowing you to dynamically adjust outputs based on predefined rules.

Example: Mutating Helm Chart Manifests

Given a configuration producing manifests from a helm chart:

charts:
  keel:
    chart_dir: ${keel:chart_dir}
    helm_params:
      namespace: ${keel:namespace}
      name: ${keel:chart_name}
      output_file: ${keel:chart_name}.yml
    helm_values: ${keel:helm_values}

You can set up the following mutations to adjust the objects the Helm chart generates:

mutations:
  bundle:
    - conditions:
        kind: [CustomResourceDefinition]
      filename: keel-crds
    - conditions:
        kind: ['*']
      filename: keel-bundle
  delete:
    - conditions:
        kind: [ConfigMap]
        metadata.name: ["keel-config"]
  patch:
    - conditions:
        kind: [CustomResourceDefinition]
      patch:
        metadata:
          annotations:
            argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true,Replace=true

Mutation Types

  • Bundle: Dictates where objects are stored.

  • filename: Redefines the file where objects matching conditions are placed.

  • Patch: Add or remove patches to objects that match given conditions.

  • Delete: Removes objects that fit the criteria.

Advanced Bundle Use

The filename parameter in the bundle mutation is an "f-format" string, accepting the resource content.

This means configurations like:

mutations:
  bundle:
    - conditions:
        kind: ['*']
      filename: "{content.metadata.namespace}/{content.metadata.name}

Can dynamically relocate generated files into subdirectories based on their namespace, adding another layer of organization.