10 Helm Charts Interview Questions and Answers

Helm Charts have become an essential tool for managing Kubernetes applications, providing a streamlined way to define, install, and upgrade even the most complex Kubernetes applications. By packaging Kubernetes resources into Helm Charts, developers and DevOps teams can easily share and deploy applications across different environments, ensuring consistency and reducing deployment errors.

This article offers a curated selection of interview questions focused on Helm Charts, designed to help you demonstrate your expertise and problem-solving abilities. Reviewing these questions will prepare you to discuss key concepts and practical applications of Helm Charts, giving you the confidence to tackle technical interviews with ease.

Helm Charts Interview Questions and Answers

1. Explain the role of values.yaml in a Helm Chart.

The values.yaml file in a Helm Chart acts as the default configuration, allowing users to override these defaults for customization. It contains key-value pairs corresponding to variables in the chart’s templates. When deploying a chart, Helm merges these values with any user-provided ones to ensure the desired configuration.

For instance, a Helm chart for a web application might have default values for the image, replica count, and resource limits:

image:
  repository: myapp
  tag: latest
replicaCount: 3
resources:
  limits:
    cpu: 100m
    memory: 128Mi

Users can override these by providing their own values.yaml or using the --set flag during deployment commands.

2. Write a Helm template snippet to define a Kubernetes Deployment resource.

A Helm template snippet for a Kubernetes Deployment resource includes metadata, spec, and template sections. Here’s an example:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Values.deployment.name }}
  labels:
    app: {{ .Values.deployment.name }}
spec:
  replicas: {{ .Values.deployment.replicas }}
  selector:
    matchLabels:
      app: {{ .Values.deployment.name }}
  template:
    metadata:
      labels:
        app: {{ .Values.deployment.name }}
    spec:
      containers:
      - name: {{ .Values.deployment.name }}
        image: {{ .Values.deployment.image }}
        ports:
        - containerPort: {{ .Values.deployment.port }}

3. What are Helm hooks and how are they used?

Helm hooks are annotations that execute tasks at specific points in the release lifecycle, such as database migrations or backups. They are defined in the metadata section of Kubernetes manifests within a Helm chart.

Example:

apiVersion: batch/v1
kind: Job
metadata:
  name: "{{ .Release.Name }}-pre-install-job"
  annotations:
    "helm.sh/hook": pre-install
spec:
  template:
    spec:
      containers:
      - name: pre-install-job
        image: busybox
        command: ['sh', '-c', 'echo Pre-install job']
      restartPolicy: Never

This job runs before the Helm chart is installed. Helm supports various hook points like pre-install, post-install, pre-delete, post-delete, pre-upgrade, and post-upgrade.

4. Explain the difference between helm install and helm upgrade.

The helm install command deploys a new release of a Helm chart, creating a new release with a unique name. It’s used for initial deployments. Conversely, helm upgrade updates an existing release with a new chart version or configuration changes, useful for rolling out updates.

5. How do you rollback a Helm release to a previous version?

To rollback a Helm release to a previous version, use the helm rollback command, specifying the release name and revision number.

Example:

helm rollback <release_name> <revision_number>

For instance, to rollback a release named my-release to revision 2:

helm rollback my-release 2

6. Describe how Helm manages dependencies between charts.

Helm manages chart dependencies using a requirements.yaml file, listing dependent charts with their versions and repositories. Running helm dependency update fetches these dependencies into the charts/ directory.

Dependencies are defined as follows:

dependencies:
  - name: <chart-name>
    version: <chart-version>
    repository: <chart-repository>

Helm supports version constraints to ensure compatibility during installation or upgrades.

7. Write a custom helper function in a Helm template and explain its use case.

Helm templates use custom helper functions to avoid repetition and simplify templates. These functions are defined in the _helpers.tpl file.

Example:

# _helpers.tpl
{{- define "mychart.fullname" -}}
{{- printf "%s-%s" .Release.Name .Chart.Name | trunc 63 | trimSuffix "-" -}}
{{- end -}}

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ include "mychart.fullname" . }}
spec:
  replicas: {{ .Values.replicaCount }}
  template:
    metadata:
      labels:
        app: {{ include "mychart.fullname" . }}
    spec:
      containers:
      - name: {{ .Chart.Name }}
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        ports:
        - containerPort: {{ .Values.service.port }}

The mychart.fullname function generates a full name for resources by combining the release and chart names, ensuring it doesn’t exceed 63 characters.

8. What are some security best practices when using Helm Charts?

When using Helm Charts, follow security best practices to ensure deployment integrity:

• Chart Provenance and Verification: Verify chart provenance to ensure they are from trusted sources. Use signed and verified charts.
• Image Security: Use trusted registries and scan images for vulnerabilities. Regularly update images with security patches.
• RBAC (Role-Based Access Control): Implement RBAC to control access, following the principle of least privilege.
• Secret Management: Avoid hardcoding sensitive information. Use Kubernetes secrets or external tools for secure handling.
• Network Policies: Define policies to control pod communication, limiting unnecessary access.
• Pod Security Policies: Enforce security standards, such as restricting privileged containers and ensuring non-root users.
• Audit and Monitoring: Enable auditing and monitoring to track changes and access, aiding in incident response.

9. How do you test a Helm Chart before deploying it?

Testing a Helm Chart before deployment ensures correct configuration and functionality. Methods include:

• Linting with helm lint: Checks for common issues and validates structure.
• Template Rendering with helm template: Renders templates locally for inspection.
• Unit Testing with Helm Unit Test Frameworks: Tools like helm-unittest validate template output under different conditions.
• Integration Testing with helm test: Runs tests in the cluster to validate resource behavior.
• Dry Run with helm install --dry-run --debug: Simulates installation without deploying resources, providing detailed output.
• Using CI/CD Pipelines: Automates testing with tools like Jenkins, GitLab CI, and GitHub Actions.

10. What are the key differences between Helm 3 and Helm 2?

Helm has evolved significantly from Helm 2 to Helm 3. Key differences include:

• Architecture: Helm 3 removes Tiller, making it a client-only tool, improving security and simplifying architecture.
• Security: Helm 3 leverages Kubernetes’ native security mechanisms, such as RBAC, addressing previous security risks.
• Release Management: Helm 3 stores release information in the same namespace as the application, improving isolation.
• CRDs (Custom Resource Definitions): Helm 3 offers better CRD support, ensuring proper management throughout the chart lifecycle.
• Library Charts: Introduces library charts for shared and reusable dependencies, promoting modularity.
• Helm Hooks: Helm 3 enhances hook handling, providing more control over execution order and lifecycle.