raynix 筆記

Use Variables in Kustomize

Variables in Kustomize are handy helpers from time to time, with these variables I can link some settings together which should share the same value all the time. Without variable I probably need to use some template engine like Jinja2 to do the same trick.

Some examples here.

In my case, there’s a bug in kustomize as of now(3.6.1) where configMap object names don’t get properly suffixed in a patch file. The issue is here. I can however use variable to overcome this bug. Imagine in a scenario I have a configMap in a base template and it will be referenced in a patch file:

# common/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - deploy.yaml
configMapGenerator:
  - name: common
    literals:
      - TEST=YES

# common/deploy.yaml
# this is not a fully functional deployment, just to demo kustomization
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test
spec:
  templates:
    spec:
      volumes: []

# test/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namespace: test
bases:
  - ../common
nameSuffix: -raynix
patchesStrategicMerge:
  - patch.yaml

# test/patch.yaml
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test
spec:
  templates:
    spec:
      volumes:
        - name: common
          configMap:
            name: common
            # this should be linked to the configMap in common/kustomization.yaml but it won't be updated with a hash and suffix.

Using variable can get around this bug. Please see the following example.

First a new configuration for kustomize is needed, to let it refer to a variable in this specific place:

# common/config.yaml
varReference:
  - kind: Deployment
    path: spec/templates/spec/volumes/configMap/name

Then a new variable can be defined as:

# common/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
# load the new configuration!
configurations:
  - config.yaml
configMapGenerator:
  - name: common
    literals:
      - TEST=YES
vars:
  - name: COMMON
    objref:
      apiVersion: v1
      kind: ConfigMap
      name: common
    fieldref:
      # this can be omitted as metadata.name is the default fieldPath 
      fieldPath: metadata.name

# test/kustomization.yaml unchanged

# test/patch.yaml
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test
spec:
  templates:
    spec:
      volumes:
        - name: common
          configMap:
            name: $(COMMON)
            # now $(COMMON) will be updated with whatever the real configmap name is

Now to test it for real:

# kustomize build test
apiVersion: v1
data:
  TEST: "YES"
kind: ConfigMap
metadata:
  name: common-raynix-75tk5fb6fc
  namespace: test
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-raynix
  namespace: test
spec:
  templates:
    spec:
      volumes:
      - configMap:
          name: common-raynix-75tk5fb6fc # <<- here we go!
        name: common

Problem solved 🙂

EDIT: Added missing configuration file.

admin

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