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Helm charts, releases, values.yaml and upgrade/rollback workflow. Kustomize overlays and bases. When to use Helm vs Kustomize for CKAD.

Helm vs Kustomize — Chart structure, template engine, overlays

1. Helm Core Concepts

Helm is a Kubernetes package manager. It packages Kubernetes manifests into Charts and manages deployments as Releases.

Helm Architecture:

  values.yaml          Chart templates
       │                    │
       ▼                    ▼
  ┌──────────────────────────────┐
  │   Helm Template Engine       │
  │   Renders YAML manifests     │
  └──────────────┬───────────────┘
                 │
                 ▼ kubectl apply
         Kubernetes Cluster
          (stored as Release)

Term	Definition
Chart	A Helm package — includes templates + default values
Release	An instance of a Chart deployed to a cluster
Repository	Where Charts are stored (like Artifact Hub, Bitnami)
Values	Configuration parameters to customize a Chart
Revision	Each install/upgrade creates a new revision

2. Helm Commands

# Add repository
helm repo add bitnami https://charts.bitnami.com/bitnami
helm repo update

# Search charts
helm search repo bitnami/nginx
helm search hub wordpress

# Install chart
helm install my-release bitnami/nginx
helm install my-release bitnami/nginx --values custom-values.yaml
helm install my-release bitnami/nginx --set image.tag=1.25

# List releases
helm list
helm list -n production

# Upgrade release
helm upgrade my-release bitnami/nginx --set replicaCount=3

# Rollback to previous revision
helm rollback my-release 1   # rollback to revision 1
helm rollback my-release     # rollback to previous revision

# Uninstall
helm uninstall my-release

# View rendered templates (dry-run)
helm template my-release bitnami/nginx
helm install my-release bitnami/nginx --dry-run

Exam tip: CKAD frequently tests helm install with --set flag (override values directly) and --values file.yaml (override from a file). Also tests helm upgrade and helm rollback. Remember that --set overrides trump --values file.

3. Kustomize

Kustomize is a tool built into kubectl that lets you customize Kubernetes manifests without templates or parameters. It uses an overlay pattern.

Kustomize Structure:
  base/
  ├── kustomization.yaml    # Base kustomization
  ├── deployment.yaml
  └── service.yaml

  overlays/
  ├── development/
  │   ├── kustomization.yaml  # Patches for dev
  │   └── replica-patch.yaml
  └── production/
      ├── kustomization.yaml  # Patches for prod
      └── replica-patch.yaml

# base/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - deployment.yaml
  - service.yaml

# overlays/production/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
bases:
  - ../../base
patches:
  - path: replica-patch.yaml
images:
  - name: myapp
    newTag: "2.0"

# Apply with kustomize
kubectl apply -k overlays/production/

# Preview rendered output
kubectl kustomize overlays/production/

4. Helm vs Kustomize

Criteria	Helm	Kustomize
Approach	Template-based (Go templates)	Overlay/patching (plain YAML)
Learning curve	Higher (template syntax)	Lower (YAML patches)
Package mgmt	Yes (charts, repos, versioning)	No
Release history	Yes (upgrade/rollback)	No built-in
Built into kubectl	No (separate binary)	Yes (`kubectl apply -k`)
Best for	Distributing apps	Env-specific customization

5. Cheat Sheet

Task	Command
Install chart with custom values	`helm install rel chart --values f.yaml`
Override a single value	`helm install rel chart --set key=val`
Rollback Helm release	`helm rollback release-name 2`
Apply kustomize overlay	`kubectl apply -k overlays/prod/`
Preview kustomize output	`kubectl kustomize overlays/prod/`

6. Practice Questions

Q1: You need to deploy a Helm chart from the "stable" repo with a custom replica count of 5. Which command accomplishes this?

A) helm deploy myapp stable/nginx --replicas=5
B) helm install myapp stable/nginx --set replicaCount=5 ✓
C) helm install myapp stable/nginx -e replicaCount=5
D) helm apply myapp stable/nginx --values replicaCount=5

Explanation: helm install uses --set flag to override values. The syntax is --set key=value. The exact key name (replicaCount) depends on the chart's values.yaml, but --set is the correct flag for inline value overrides.

Q2: A team uses Kustomize with a base configuration and production/staging overlays. Which command applies the production overlay?

A) kubectl apply -f overlays/production/
B) kubectl kustomize overlays/production/ | kubectl apply -f -
C) kubectl apply -k overlays/production/ ✓
D) kustomize apply overlays/production/

Explanation: kubectl apply -k (note -k not -f) is the built-in way to apply a kustomization directory. Option B also works but is more verbose. The -k flag tells kubectl to process the directory as a Kustomize configuration.

Q3: After a Helm upgrade introduces a bug, you need to revert to the previous working state. What is the correct approach?

A) kubectl rollout undo deployment/myapp
B) helm install --replace myapp stable/nginx
C) helm rollback myapp ✓
D) helm upgrade myapp --version=previous