DEMO Kustomize Controller Kustomize Overlay

Welcome to this hands-on tutorial on using the Kustomize controller to apply overlays via Flux CD. In this lesson, you’ll learn how to:

1. Switch to the 3-demo branch containing a kustomization.yaml
2. Create a Flux GitRepository source
3. Define a Flux Kustomization resource
4. Verify the setup with Flux commands
5. Inspect the deployed Kubernetes resources
6. View the updated Block Buster application

By the end, you’ll have a working overlay that skips the build phase and applies changes automatically.

1. Switch to the 3-demo Branch

First, clone or navigate to your application source and check out the 3-demo branch where the kustomization.yaml is already defined:

cd ~/bb-app-source
git checkout 3-demo

You should see:

Branch '3-demo' set up to track remote branch '3-demo' from 'origin'.
Switched to a new branch '3-demo'

List the directory to confirm all files:

ls

Contents of kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - deployment.yml
  - service.yml
  - namespace.yml

2. Create a Git Source in the Flux Cluster

Switch to your Flux configuration repository:

cd ~/block-buster/flux-clusters/dev-cluster/

Define a GitRepository resource that points to branch 3-demo of your app repo:

flux create source git 3-demo-source-git-bb-app \
  --url https://github.com/sidd-harth-2/bb-app-source \
  --branch 3-demo \
  --interval 10s \
  --export > 3-demo-source-git-bb-app.yaml

3-demo-source-git-bb-app.yaml:

apiVersion: source.toolkit.fluxcd.io/v1beta2
kind: GitRepository
metadata:
  name: 3-demo-source-git-bb-app
  namespace: flux-system
spec:
  interval: 10s
  ref:
    branch: 3-demo
  url: https://github.com/sidd-harth-2/bb-app-source

3. Create the Kustomization Resource

Next, define a Flux Kustomization that applies the overlay found under kustomize:

flux create kustomization 3-demo-kustomize-git-bb-app \
  --source GitRepository/3-demo-source-git-bb-app \
  --path kustomize \
  --target-namespace 3-demo \
  --prune true \
  --interval 10s \
  --export > 3-demo-kustomize-git-bb-app.yaml

Contents of 3-demo-kustomize-git-bb-app.yaml:

apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
kind: Kustomization
metadata:
  name: 3-demo-kustomize-git-bb-app
  namespace: flux-system
spec:
  interval: 10s
  path: ./kustomize
  prune: true
  sourceRef:
    kind: GitRepository
    name: 3-demo-source-git-bb-app
  targetNamespace: 3-demo

Commit and push both Flux manifests:

git add 3-demo-source-git-bb-app.yaml 3-demo-kustomize-git-bb-app.yaml
git commit -m "Add 3-demo overlay with Kustomization"
git push

4. Verify with Flux

Check that the Git source is registered:

flux get sources git

Expected output:

NAME                        REVISION              SUSPENDED READY MESSAGE
2-demo-source-git-bb-app    2-demo@sha1:7dfa8105  False     True  stored artifact for revision '2-demo@sha1:7dfa8105'
3-demo-source-git-bb-app    3-demo@sha1:990e6de9  False     True  stored artifact for revision '3-demo@sha1:990e6de9'
flux-system                 main@sha1:548f1930    False     True  stored artifact for revision 'main@sha1:548f1930'

Then confirm the overlay is applied:

flux get kustomizations

Expected output:

NAME                            REVISION              SUSPENDED READY MESSAGE
2-demo-kustomize-git-bb-app     2-demo@sha1:7dfa8105  False     True  Applied revision: 2-demo@sha1:7dfa8105
3-demo-kustomize-git-bb-app     3-demo@sha1:990e6de9  False     True  Applied revision: 3-demo@sha1:990e6de9
flux-system                      main@sha1:548f1930    False     True  Applied revision: main@sha1:548f1930

5. Inspect Deployed Resources

List all namespaces to ensure 3-demo exists:

kubectl get ns

View resources in the 3-demo namespace:

kubectl get all -n 3-demo

Sample output:

NAME                                         READY   STATUS    RESTARTS AGE
pod/block-buster-68f7ccdfd7-62w6f            1/1     Running   0        69s

NAME                           TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
service/block-buster-service   NodePort   10.101.115.232  <none>        80:30008/TCP   69s

NAME                             READY UP-TO-DATE AVAILABLE AGE
deployment.apps/block-buster      1/1   1          1         69s

NAME                                         DESIRED CURRENT READY AGE
replicaset.apps/block-buster-68f7ccdfd7     1       1       1     69s

6. View the Updated Application

Open your browser to http://<node-ip>:30008. You’ll notice that the game now shows three lives instead of one:

Links and References

• Flux CD Documentation
• Kustomize Overview
• GitOps with Flux CD