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:

Switch to the 3-demo branch containing a kustomization.yaml
Create a Flux GitRepository source
Define a Flux Kustomization resource
Verify the setup with Flux commands
Inspect the deployed Kubernetes resources
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

File	Description
deployment.yml	Deployment specification for block-buster
service.yml	Service exposing your application
namespace.yml	Namespace definition for isolation
kustomization.yaml	Kustomize resource list for overlay

Contents of kustomization.yaml:

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

Because the kustomization.yaml is present, the Kustomize controller will skip the normal build phase and apply resources directly.

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

Flux will poll the Git repository every 10 seconds and store an artifact for the specified branch.

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:

The image shows a "Block Buster" game interface with colorful blocks, a ball, and a paddle. It also displays technical details like pod name, IP, and app version on the left.

GitOps Overview

Flux Overview

Source and Kustomize Controller

Helm Controller and OCI Registry

Image Automation Controller

Secret Management & Sign Verification

Notification Controller

Monitoring & User Interface

DEMO Kustomize Controller Kustomize Overlay

1. Switch to the `3-demo` Branch

2. Create a Git Source in the Flux Cluster

3. Create the Kustomization Resource

4. Verify with Flux

5. Inspect Deployed Resources

6. View the Updated Application

Links and References

Watch Video

Practice Lab

​1. Switch to the 3-demo Branch

​2. Create a Git Source in the Flux Cluster

​3. Create the Kustomization Resource

​4. Verify with Flux

​5. Inspect Deployed Resources

​6. View the Updated Application

​Links and References

Watch Video

Practice Lab

1. Switch to the `3-demo` Branch

2. Create a Git Source in the Flux Cluster

3. Create the Kustomization Resource

4. Verify with Flux

5. Inspect Deployed Resources

6. View the Updated Application

Links and References