Transformer Configurations

Kustomize computes the configuration of a resource by applying a series of transformers:

namespace transformer
prefix/suffix transformer
label transformer
annotation transformer
name reference transformer
variable reference transformer

Each transformer takes a list of resources and modifies certain fields in the resource based upon the transformer's configuration. A transformer's configuration is a list of fieldSpec, represented in YAML format.

FieldSpec

FieldSpec is a type that represents a path to a field in one kind of resource, such as Job.

group: some-group
version: some-version
kind: some-kind
path: path/to/the/field
create: false

If create is set to true, the transformer creates the path to the field in the resource if the path is not already found. This is most useful for label and annotation transformers, where the path for labels or annotations may not be set before the transformation.

Prefix/suffix transformer

The prefix/suffix transformer adds a prefix/suffix to the metadata/name field for all resources. Here is the default prefix transformer configuration:

namePrefix:
- path: metadata/name

Label transformer

The label transformer adds labels to the metadata/labels field for all resources. It also adds labels to the spec/selector field in all Service resources as well as the spec/selector/matchLabels field in all Deployment resources.

commonLabels:
- path: metadata/labels
  create: true

- path: spec/selector
  create: true
  version: v1
  kind: Service

- path: spec/selector/matchLabels
  create: true
  kind: Deployment

Name reference transformer

Name reference transformer's configuration is different from all other transformers. It contains a list of nameReferences, which represent all of the possible fields that a type could be used as a reference in other types of resources. A nameReference contains a type such as ConfigMap as well as a list of fieldSpecs where ConfigMap is referenced in other resources. Here is an example.

kind: ConfigMap
version: v1
fieldSpecs:
- kind: Pod
  version: v1
  path: spec/volumes/configMap/name
- kind: Deployment
  path: spec/template/spec/volumes/configMap/name
- kind: Job
  path: spec/template/spec/volumes/configMap/name

Name reference transformer's configuration contains a list of nameReferences for resources such as ConfigMap, Secret, Service, Role, and ServiceAccount. Here is an example configuration:

nameReference:
- kind: ConfigMap
  version: v1
  fieldSpecs:
  - path: spec/volumes/configMap/name
    version: v1
    kind: Pod
  - path: spec/containers/env/valueFrom/configMapKeyRef/name
    version: v1
    kind: Pod
  # add additional paths to resource fields
- kind: Secret
  version: v1
  fieldSpecs:
  - path: spec/volumes/secret/secretName
    version: v1
    kind: Pod
  - path: spec/containers/env/valueFrom/secretKeyRef/name
    version: v1
    kind: Pod

Customizing transformer configurations

Kustomize has a default set of transformer configurations. You can view the default transformer configurations by saving them to a local directory by calling kustomize config save -d.

Kustomize also supports adding extra transformer configurations by adding configuration files in the kustomization.yaml file. This tutorial shows how to customize those configurations to:

support a CRD type
add extra fields for variable substitution
add extra fields for name reference