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Kustomize vs Helm

This article compares Helm and Kustomize, two tools for managing Kubernetes manifests, highlighting their strengths, workflows, and trade-offs.

In this article, we’ll compare Helm and Kustomize—two popular methods for managing Kubernetes manifests across different environments. Understanding their strengths, workflows, and trade-offs will help you select the best fit for your project.

How Helm Works: Go-Templating in YAML

Helm uses Go templates to inject dynamic values into your Kubernetes manifests. Placeholders in the form of {{ .Values.variable }} are replaced at deploy time based on a values.yaml file.

```yaml theme={null}

templates/nginx-deployment.yaml

apiVersion: apps/v1 kind: Deployment metadata: name: {{ .Values.name }} spec: replicas: {{ .Values.replicaCount }} selector: matchLabels: app: {{ .Values.name }} template: metadata: labels: app: {{ .Values.name }} spec: containers: - name: {{ .Chart.Name }} image: "nginx:{{ .Values.image.tag }}"

Text Only
```yaml  theme={null}
# values.yaml
replicaCount: 1
image:
  tag: "2.4.4"
name: "my-app"

When you run helm install my-app ./chart -f values.yaml, Helm merges the values into the templates, producing valid Kubernetes YAML:

```yaml theme={null} apiVersion: apps/v1 kind: Deployment metadata: name: my-app spec: replicas: 1 selector: matchLabels: app: my-app template: metadata: labels: app: my-app spec: containers: - name: my-chart image: "nginx:2.4.4"

Text Only
<Callout icon="lightbulb" color="#1CB2FE">
  Use `--values` (or `-f`) to specify different environment files, e.g., `-f values.prod.yaml`.
</Callout>

## Helm Chart Structure

A typical Helm chart directory might look like:

```text  theme={null}
k8s/
├── environments/
│   ├── values.dev.yaml
│   ├── values.stg.yaml
│   └── values.prod.yaml
└── templates/
    ├── nginx-deployment.yaml
    ├── nginx-service.yaml
    ├── db-deployment.yaml
    └── db-service.yaml

  • templates/: Kubernetes manifests with Go templating syntax.
  • environments/: Separate values.*.yaml files for each environment.

Feature Comparison

Feature Helm Kustomize
Template Syntax Go templates ({{ }}) Pure YAML overlays and patches
Conditional Logic & Loops ✔️ Supports if, range, custom functions ❌ Not supported
Packaging & Versioning ✔️ Full-fledged chart packaging, dependencies, hooks ❌ No built-in packaging
Valid YAML Before Rendering ❌ Not valid until helm template runs ✔️ Always valid YAML
Native Kubernetes Integration ✔️ Widely adopted, independent CLI ✔️ Built into kubectl

Complex Helm charts with extensive logic can become hard to read and maintain. Ensure you document templates and values clearly.

Trade-offs: When to Use Each Tool

  • Use Helm if\ • You need advanced templating (conditionals, loops, custom functions)\ • You want packaging, versioning, and chart dependencies\ • You require lifecycle hooks (e.g., pre-install, post-upgrade)

  • Use Kustomize if\ • You prefer pure YAML without an extra rendering step\ • You want easy-to-read overlays and patches\ • Your customization needs are straightforward (e.g., changing images, labels)

Balance your project’s complexity and team familiarity when choosing between the two.

The image is a slide comparing Kustomize and Helm, highlighting Helm's features such as being a package manager, providing conditionals, loops, functions, and hooks, and noting that Helm templates are not valid YAML due to Go templating syntax.

References