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What is Kustomize, and how does it differ from Helm?

Infrastructure as Code (Terraform, Ansible) · Advanced level

Answer

Kustomize customizes Kubernetes YAML without templates by composing bases and overlays with patches, generators, labels, and name transformations. Helm packages and templates charts using values. Kustomize is patch-oriented and YAML-native; Helm is package and template-oriented.

Technical explanation

Kustomize overlays are easier to review because the base Kubernetes YAML remains visible.

Helm is better for reusable application packaging and chart distribution.

Both can be part of GitOps, but uncontrolled template complexity hurts reviewability.

Keep source manifests or IaC definitions readable enough that reviewers can understand the final desired state.

Use overlays, modules, or roles for reuse, but keep environment-specific differences explicit and reviewable.

Validate generated output in CI before applying it through kubectl, Argo CD, Terraform, or Ansible.

Hands-on example

1. Create a Kustomize base and overlay for: What is Kustomize, and how does it differ from Helm?

2. Base files:

base/deployment.yaml

base/service.yaml

base/kustomization.yaml

base/kustomization.yaml:

resources:

- deployment.yaml

- service.yaml

commonLabels:

app.kubernetes.io/name: payments

3. prod overlay:

resources:

- ../../base

namePrefix: prod-

namespace: payments-prod

images:

- name: ghcr.io/company/payments

newTag: 1.8.4

configMapGenerator:

- name: app-config

literals:

- LOG_LEVEL=info

patches:

- path: replica-patch.yaml

4. Render and apply:

kubectl kustomize overlays/prod

kubectl diff -k overlays/prod

kubectl apply -k overlays/prod

5. In GitOps, point Argo CD at overlays/prod and let it render, compare, and sync the desired state.

More Infrastructure as Code (Terraform, Ansible) interview questions

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• What is the difference between declarative and imperative IaC, and where do Terraform and Ansible fall?
• What is the difference between configuration management and provisioning?
• What is Terraform, and what is the core plan/apply workflow?
• What does terraform init do?
• What is the Terraform state file, and why is it critical?
• Why should state be stored remotely, and what backend would you use on AWS?
• What is state locking, and why does it matter for teams?

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