Demo Kustomize Controller Kustomize Overlay

This lesson shows how to use a Kustomization resource that points at an existing kustomization.yaml (a Kustomize overlay) stored in a Git branch. When the Kustomization references a path that already contains an overlay, the Kustomize Controller will validate and apply the manifests directly — skipping overlay generation — which simplifies your GitOps workflow. Overview — what you will do:

Switch to the 3-demo branch (this branch contains a kustomization.yaml and plain Kubernetes manifests).
Create a Flux GitRepository source that references the 3-demo branch.
Create a Flux Kustomization that points to the overlay path in that source.
Observe Flux fetching the branch and applying the namespace and application resources.

1. Switch to the 3-demo branch

Checkout the branch that contains the overlay and the manifests:

# from your local bb-app-source repository
git checkout 3-demo
# Example output:
# Branch '3-demo' set up to track remote branch '3-demo' from 'origin'.
# Switched to branch '3-demo'

On this branch the repository contains, for example in ./kustomize:

deployment.yml
service.yml
namespace.yml
kustomization.yaml

Example kustomization.yaml (overlay file) in the repo:

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

When a Kustomization resource points at a Git source path that already includes a kustomization.yaml (or a kustomize directory with an overlay), Flux will use that overlay directly and will not generate a separate overlay.

2. Create a GitRepository source (Flux)

From your Flux cluster repo directory (for example block-buster/flux-clusters/dev-cluster) create a GitRepository resource that references the 3-demo branch and export it to YAML:

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.yml

The exported GitRepository YAML will look like:

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

Save and commit 3-demo-source-git-bb-app.yml to your cluster manifests repository (if you manage Flux configuration in Git), or apply it directly to your cluster so Flux can start reconciling that source.

3. Create a Flux Kustomization that points at the overlay

Create a Kustomization resource that points to the overlay path (for this example ./kustomize) and export it:

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

The exported Kustomization YAML will resemble:

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

Save and commit 3-demo-kustomize-git-bb-app.yml to your Flux manifests repository (or apply it) so Flux can reconcile and apply the overlay.

Ensure the target-namespace does not conflict with existing resources and that you have appropriate RBAC permissions for Flux to create or manage the specified namespace and resources.

4. Observe Flux fetching and applying the overlay

After Flux reconciles the GitRepository and Kustomization: Check Git sources:

# show Git sources
flux get sources git

Example 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'

Check Kustomizations:

# show Kustomizations
flux get kustomizations

Example 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

Verify the namespace and deployed resources:

kubectl get ns
kubectl get all -n 3-demo

In this demo branch, the application has a gameplay change: the player starts with three lives instead of one.

A web screenshot of a "BLOCK BUSTER" breakout-style game showing colored brick rows, a paddle at the bottom and a bouncing ball. The top panel displays pod information like Pod Name, Pod IP, Namespace and app version.

That’s it — because the repo already contained the overlay at the referenced path, the Kustomize Controller applied the manifests directly from the repo: validating and reconciling resources without rebuilding the overlay.

Quick reference

Resource	Purpose	Example (export filename)
GitRepository	Points Flux to the Git branch containing overlay and manifests	`3-demo-source-git-bb-app.yml`
Kustomization	Tells Flux which path to apply from the Git source and how to apply it	`3-demo-kustomize-git-bb-app.yml`

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 GitRepository source (Flux)

3. Create a Flux Kustomization that points at the overlay

4. Observe Flux fetching and applying the overlay

Quick reference

Watch Video

Practice Lab

​1. Switch to the 3-demo branch

​2. Create a GitRepository source (Flux)

​3. Create a Flux Kustomization that points at the overlay

​4. Observe Flux fetching and applying the overlay

​Quick reference

Watch Video

Practice Lab

1. Switch to the 3-demo branch

2. Create a GitRepository source (Flux)

3. Create a Flux Kustomization that points at the overlay

4. Observe Flux fetching and applying the overlay

Quick reference