Helm Advanced Questions

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Level: Advanced

🔴 Complex Scenarios & Architecture.

Tackle high-level design, production-grade scaling, security, and advanced internals.

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1. What is a Library Chart?

A chart that provides templates and functions but creates no release artifacts itself.

Include type: library in Chart.yaml. Used to share reusable snippets (like standard Deployment templates) across many application charts to enforce consistency (DRY principle).

2. How does Helm support OCI (Open Container Initiative) registries?

Helm 3 can store and share charts as OCI artifacts (like Docker images).

Commands: * helm registry login * helm push chart-0.1.0.tgz oci://myregistry.azurecr.io/charts * helm install my-app oci://myregistry.azurecr.io/charts/mychart --version 0.1.0

3. Explain 'Provenance' and chart signing.

Provenance enables verifying the integrity and origin of a chart.

Maintainers create a provenance file (.prov) consisting of a PGP signature. Users can verify it using helm verify or --verify during install to ensure the package hasn't been tampered with.

4. How do you manage secrets in Helm?

Helm does not encrypt secrets by default; they are stored as base64 encoded strings.

For production, use external plugins like helm-secrets (with SOPS) or integrate with External Secrets Operator / HashiCorp Vault so you don't commit raw secrets to git.

5. What is the helm-diff plugin and why is it crucial?

It shows a text diff of what will change before you upgrade.

Running helm diff upgrade [release] [chart] helps separate the intended changes from accidental ones, preventing configuration drift in production.

6. How do you handle CRD upgrades since Helm ignores them?

Manual intervention or separate chart.

Best practice: Use a separate "infrastructure" chart just for CRDs, or use a specific job/hook in the main chart to apply updated CRD definitions using kubectl apply logic, though this ignores the safety of Helm's lifecycle.

7. Describe the 'Umbrella Chart' pattern.

A parent chart that contains no templates of its own but defines multiple subcharts as dependencies.

It acts as a composed application definition, allowing you to deploy an entire stack (Frontend + Backend + DB) with a single helm install command and unified values.yaml.

8. How can you modify a chart that you don't own (e.g., from Bitnami) without forking it?

Using the 'Post-Rendering' feature.

helm install ... --post-renderer ./kustomize. This allows you to patch the fully rendered manifests (e.g., adding labels or sidecars) using a tool like Kustomize before they are sent to the API server.

9. What is the maximum size of a Helm release, and why?

Limited by the Kubernetes Secret size limit (approx 1MB).

Helm stores release history as Secrets (or ConfigMaps). If a release contains massive manifests (thousands of lines), it may fail. Solution: Use SQL storage backend for Helm (advanced) or split the chart.

10. How do subchart values work with global values?

Values can be passed to subcharts via the subchart's name key.

Additionally, the special global node (.Values.global) defaults to being accessible in all charts (parent and subcharts). This is perfect for shared settings like global.imageRegistry.

11. How do you optimize Helm template performance?

Avoid heavy lookup calls and excessive context switching.

Use define to compute complex values once and reuse them. Keep chart sizes manageable.

12. What are 'Starter Packs' in Helm?

Scaffolding templates used by helm create.

Instead of the generic default structure, you can define your own starter pack (directory) to enforce company standards when developers start a new chart.

13. How do you implement 'Blue/Green' or 'Canary' deployments with Helm?

Helm itself just updates resources; it doesn't natively orchestrate traffic shifting.

You typically pair Helm with a progressive delivery controller like Argo Rollouts or Flagger. Helm deploys the Rollout resource, and the controller handles the traffic weight shifting.

14. How do you secure Helm's access to the cluster?

Helm client uses the user's kubeconfig context.

RBAC policies must be applied to the user/ServiceAccount running Helm. They need permissions not just for the app resources (Deployment, Service) but also for Secrets (to store release history).

15. What happens if a pre-install hook fails?

The installation moves to a FAILED state.

Helm will not proceed to deploy the main resources. You usually need to purge/uninstall the failed release before retrying.

16. How do you reference images from a private registry in a chart?

Use imagePullSecrets.

You define the name of the Kubernetes Secret containing credentials in your values.yaml, and the template injects it into the Pod spec.

17. Can you query the capabilities of the Kubernetes cluster inside a template?

Yes, using .Capabilities.

Example: {{ if .Capabilities.APIVersions.Has "autoscaling/v2" }} allows you to render different manifests based on whether the cluster supports a specific API version.

18. How do you troubleshoot the 'release: already exists' error?

It means a history Secret for that name exists but is likely in a weird state (e.g., from a failed previous install).

Check helm list -A (or helm list --all to see failed/uninstalled records). If safe, use helm uninstall or manually delete the release secret.

19. How do you persist data across Helm uninstalls?

Use helm.sh/resource-policy: keep annotation.

Adding this annotation to a resource (like a PVC or PV) tells Helm to abandon the resource (leave it orphaned) instead of deleting it during an uninstall.

20. How do you unit test a Helm chart?

Using the helm-unittest plugin.

It allows you to write test suites in YAML that assert the rendered output (e.g., "Deployment must have 3 replicas") without needing a real cluster.

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