Helm Chart Style Guide

This skill provides standardized conventions for authoring and maintaining Helm charts, with a focus on:

• Global registry override using .Values.global.image.registry
• Clear, minimal templating
• Consistent image: blocks for all containers

When to Use

Activate this skill when:

• Creating new Helm charts
• Reviewing or modifying existing Helm charts
• Configuring image registries for air-gapped environments
• Setting up multi-chart deployments with Helmfile

Image Configuration Best Practices

All charts must support the top-level configuration for global image settings.

global:
  image:
    registry: registry.mycompany.com

This enables centralized control of image sources across all dependencies and microservices.

Consistent Image Blocks

All charts should follow a consistent image: block for every containerized application.

Fields should be templated for registry, repository, tag, pullPolicy, and pullSecrets for all containers.

Every chart must define all image values with reasonable defaults in values.yaml:

prometheus:
  image:
    registry: docker.io
    repository: prom/prometheus
    tag: v2.52.0
    pullPolicy: IfNotPresent

Templating Pattern for Registry Override

Use a registry value at the top of the template. This pattern ensures ability to use internal registries (e.g., registry.mycompany.com) for air-gapped environments or mirrored image sources:

{{- $registry := .Values.prometheus.image.registry | default .Values.global.image.registry | default "docker.io" -}}
image:
  registry: {{ $registry }}
  repository: {{ .Values.prometheus.image.repository }}
  tag: {{ .Values.prometheus.image.tag }}
  pullPolicy: {{ .Values.prometheus.image.pullPolicy }}

Templating Conventions

Template only when necessary. Keep templates readable and manageable by avoiding over-templating.

Template:

• Labels
• Annotations
• Resource requests and limits for CPU and memory for each container
• Service port numbers and names

Avoid Templating:

• Most values already present in values.yaml unless dynamically constructed

Linting & Validation

• Run helm lint before commits
• Use helm template for rendering checks
• Ensure values.yaml and Chart.yaml are fully in sync with templated expectations

Automated Chart Testing with ct

Use the chart-testing tool (ct) to automate linting, installation, and upgrade checks for charts.

Installing ct

Install ct (chart-testing) locally:

brew install helm/chart-testing/ct
# or via Docker:
# docker pull quay.io/helmpack/chart-testing

Using ct

ct lint --config charts/your-chart/ct.yaml
ct install --config charts/your-chart/ct.yaml

Typical workflow:

• Lint all charts: ct lint --all
• Install and test charts: ct install --all
• Test only changed charts: ct lint --charts charts/your-chart

Best Practices

• Always run ct lint and ct install before submitting a PR
• Ensure ct.yaml is up to date with chart locations and test settings
• Integrate ct into CI pipelines for automated validation
• Address all errors and warnings before merging

Helmfile Multi-Chart Management

Helmfile enables declarative management of multiple Helm charts and environments.

Installing Helmfile

brew install helmfile
# or via Docker:
# docker run --rm -v $PWD:/apps -w /apps ghcr.io/helmfile/helmfile:latest helmfile --help

Using Helmfile

• Define releases and environments in helmfile.yaml or helmfile.d/*.yaml
• Use values: blocks to layer configuration and support overrides per environment
• Run helmfile lint to validate all releases and values
• Apply changes with helmfile apply (dry-run with --dry-run first)
• Sync state with helmfile sync to ensure all releases match the desired state

Helmfile Best Practices

• Keep environment-specific values in separate files (e.g., values-prod.yaml, values-dev.yaml)
• Use secrets: for sensitive values, leveraging helm-secrets if needed
• Prefer referencing charts by version for reproducibility
• Use helmfile diff before applying changes to preview impact
• Document all environments and overrides clearly
• Validate with helmfile lint and test deployments in CI where possible

Naming Conventions

Chart names must be lower case letters and numbers. Words may be separated with dashes (-).

Neither uppercase letters nor underscores can be used in chart names. Dots should not be used in chart names.

YAML files should be indented using two spaces (and never tabs).

CRDs

When working with Custom Resource Definitions (CRDs):

• There is a declaration of a CRD (YAML file with kind: CustomResourceDefinition)
• There are resources that use the CRD (resources with the CRD's apiVersion and kind)

For a CRD, the declaration must be registered before any resources of that CRD's kind(s) can be used.

With Helm 3, use the special crds directory in your chart to hold your CRDs. These CRDs are not templated, but will be installed by default when running helm install. If the CRD already exists, it will be skipped with a warning. Use --skip-crds flag to skip CRD installation.

Note: There is no support for upgrading or deleting CRDs using Helm.

Standard Labels

The following labels are recommended for Helm charts:

An item of metadata should be a label if:

• It is used by Kubernetes to identify this resource
• It is useful for operators to query the system

If an item of metadata is not used for querying, it should be set as an annotation instead.

Images

A container image should use a fixed tag or the SHA of the image. Never use latest, head, canary, or other "floating" tags.

Pods

All PodTemplate sections should specify a selector:

selector:
  matchLabels:
    app.kubernetes.io/name: MyName
template:
  metadata:
    labels:
      app.kubernetes.io/name: MyName

This makes the relationship between the set and the pod explicit and prevents breaking changes when labels change.

RBAC Configuration

RBAC and ServiceAccount configuration should happen under separate keys:

rbac:
  # Specifies whether RBAC resources should be created
  create: true

serviceAccount:
  # Specifies whether a ServiceAccount should be created
  create: true
  # The name of the ServiceAccount to use
  # If not set and create is true, a name is generated using the fullname template
  name:

For complex charts with multiple ServiceAccounts:

someComponent:
  serviceAccount:
    create: true
    name:
anotherComponent:
  serviceAccount:
    create: true
    name:

rbac.create should default to true. Users who wish to manage RBAC access controls themselves can set this to false.

ServiceAccount Helper Template

{{/*
Create the name of the service account to use
*/}}
{{- define "mychart.serviceAccountName" -}}
{{- if .Values.serviceAccount.create -}}
    {{ default (include "mychart.fullname" .) .Values.serviceAccount.name }}
{{- else -}}
    {{ default "default" .Values.serviceAccount.name }}
{{- end -}}
{{- end -}}

Templates Directory Structure

The templates/ directory should be structured as follows:

• Template files should have the extension .yaml if they produce YAML output
• The extension .tpl may be used for template files that produce no formatted content
• Template file names should use dashed notation (my-example-configmap.yaml), not camelcase
• Each resource definition should be in its own template file
• Template file names should reflect the resource kind (e.g., foo-pod.yaml, bar-svc.yaml)

Defined Template Names

All defined template names should be namespaced to avoid collisions with subcharts:

Correct:

{{- define "nginx.fullname" }}
{{/* ... */}}
{{ end -}}

Incorrect:

{{- define "fullname" -}}
{{/* ... */}}
{{ end -}}

Formatting Templates

Templates should be indented using two spaces (never tabs).

Template directives should have whitespace after the opening braces and before the closing braces:

Correct:

{{ .foo }}
{{ print "foo" }}
{{- print "bar" -}}

Incorrect:

{{.foo}}
{{print "foo"}}
{{-print "bar"-}}

Checklist for Chart Review

Structure

• Chart name is lowercase with dashes
• YAML files use 2-space indentation
• Templates use .yaml extension (or .tpl for helpers)
• Each resource is in its own template file

Image Configuration

• Supports global.image.registry override
• Uses fixed tags or SHAs, not floating tags
• All image fields are configurable in values.yaml

Labels & Selectors

• Includes recommended standard labels
• PodTemplate sections have proper selectors

RBAC

• RBAC and ServiceAccount are separate config sections
• rbac.create defaults to true
• ServiceAccount helper template is properly namespaced

Validation

• Passes helm lint
• Passes ct lint
• values.yaml and Chart.yaml are in sync