Kustomize vs Helm: Key Differences and When to Use Each

Kustomize and Helm are tools for managing Kubernetes configurations; Kustomize focuses on overlaying and patching YAML files without templates, while Helm uses templating and packaging with charts. Choose Kustomize for simpler, native Kubernetes customization and Helm for complex deployments with reusable charts.

Quick Comparison

This table summarizes the main differences between Kustomize and Helm across key factors.

Factor	Kustomize	Helm
Configuration Style	YAML overlays and patches	Templated YAML with Go templates
Packaging	No packaging, works on raw manifests	Packages as charts with dependencies
Templating	No templating, uses strategic merge patches	Full templating with variables and functions
Complexity	Simpler, native Kubernetes approach	More complex, supports advanced logic
Use Case	Customizing existing manifests easily	Deploying reusable, shareable applications
Tool Integration	Built into kubectl since v1.14	Separate CLI tool with rich ecosystem

Key Differences

Kustomize works by layering and patching plain Kubernetes YAML files. It does not use templates but instead applies overlays and strategic merge patches to base manifests. This makes it simple and native to Kubernetes, as it uses standard YAML without introducing new syntax.

In contrast, Helm uses a templating engine based on Go templates. It allows you to create dynamic manifests with variables, conditionals, and loops. Helm packages these templates into charts, which can include dependencies and versioning, making it suitable for complex applications.

While Kustomize is integrated into kubectl and focuses on customization of existing manifests, Helm is a full package manager for Kubernetes applications, supporting installation, upgrades, and rollbacks with a rich ecosystem of charts.

Code Comparison

Here is how you create a simple deployment with a customized image tag using Kustomize.

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: nginx:1.14.2
---
# kustomization.yaml
resources:
- deployment.yaml
images:
- name: nginx
  newTag: 1.16.0

Output

kubectl apply -k .
# This applies the deployment with image nginx:1.16.0 replacing nginx:1.14.2

Helm Equivalent

Here is how you create the same deployment using a Helm chart with a customizable image tag.

yaml

# templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Release.Name }}-myapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: {{ .Release.Name }}-myapp
  template:
    metadata:
      labels:
        app: {{ .Release.Name }}-myapp
    spec:
      containers:
      - name: myapp
        image: nginx:{{ .Values.image.tag }}

# values.yaml
image:
  tag: 1.16.0

# Command to install
helm install myrelease .

Output

NAME: myrelease
STATUS: deployed
# Deployment created with image nginx:1.16.0

When to Use Which

Choose Kustomize when you want a simple, native way to customize Kubernetes YAML files without learning templating. It is ideal for small to medium projects or when you want to patch existing manifests easily.

Choose Helm when you need a full-featured package manager with templating, versioning, and dependency management. Helm is best for complex applications, reusable charts, and when you want to share or distribute your Kubernetes apps.

Key Takeaways

Kustomize customizes plain YAML with overlays and patches, no templating needed.

Helm uses templated charts for complex, reusable Kubernetes applications.

Use Kustomize for simple customization and Helm for full application packaging.

Kustomize is built into kubectl; Helm requires a separate CLI tool.

Helm supports versioning, dependencies, and advanced deployment features.