Helm Chart

Helm Chart Work Guide

Working on the Astronomer APC Chart

APC is an umbrella chart: templates live at the umbrella level (under templates/ and charts/<chart>/templates/), sub-charts are tightly coupled and not intended to be used standalone, and a single values.yaml controls the entire platform. See docs/architecture.md for the installation modes (unified / control / data), per-mode component inventory, and cross-plane communication.

For testing, use the chart-tests skill — it covers render_chart(), sub-chart values nesting, parametrized tests, and uv run pytest usage.

Template layout

Three filename styles coexist in this repo. When adding a new template, follow whichever style the surrounding chart already uses — we do not retroactively rename existing files.

Style 1 — component-prefixed bare files. Used in single-component sub-charts: alertmanager, external-es-proxy, external-secrets, grafana, kube-state, pgbouncer, prometheus, vector. Filenames are <chart>[-feature]-<k8s_object>.yaml directly under templates/.

charts/alertmanager/templates/alertmanager-statefulset.yaml
charts/prometheus/templates/prometheus-alerts-configmap.yaml
charts/vector/templates/vector-daemonset.yaml

Style 2 — bare object-name files. Used in sub-charts derived from upstream third-party charts: postgresql, nats, prometheus-postgres-exporter. Filenames are just <k8s_object>.yaml. Keep this style for these charts so future re-syncs with upstream stay easy.

charts/postgresql/templates/statefulset.yaml
charts/nats/templates/configmap.yaml
charts/prometheus-postgres-exporter/templates/deployment.yaml

Style 3 — sub-component subdirectories. Used in charts that contain multiple distinct sub-components: astronomer (Houston, Commander, Astro UI, Registry, Pilot, …), nginx (controlplane / dataplane variants), elasticsearch (master / data / client / curator / exporter), airflow-operator (rbac / manager / webhooks / …). Each sub-component lives in its own subdirectory and the sub-component name is repeated in the filename — the redundancy keeps the file identifiable from its basename alone.

charts/astronomer/templates/commander/commander-deployment.yaml
charts/astronomer/templates/houston/api/houston-deployment.yaml
charts/nginx/templates/controlplane/nginx-cp-deployment.yaml
charts/elasticsearch/templates/master/es-master-statefulset.yaml

In all three styles: lowercase with hyphens, helpers live in _helpers.yaml (or _helpers.tpl), and the K8s object kind (deployment, configmap, networkpolicy, service, serviceaccount, role, rolebinding, ingress, …) is part of the filename so resources are easy to locate.

Probe customization

Every container should expose livenessProbe and readinessProbe as overridable values so operators can tune health checks for their environments (slow-starting components, alternative probe methods, higher failure thresholds).

# In the deployment template
{{- if .Values.myComponent.livenessProbe }}
livenessProbe: {{ tpl (toYaml .Values.myComponent.livenessProbe) $ | nindent 12 }}
{{- else }}
livenessProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10
{{- end }}

# In values.yaml
myComponent:
  # -- Custom liveness probe configuration (overrides default)
  livenessProbe: {}
  # -- Custom readiness probe configuration (overrides default)
  readinessProbe: {}

Values Documentation

Use helm-docs comment pattern:

# -- Brief description of what this value does
# @default -- value
myKey: value

myObject:
  # -- Nested key description
  nestedKey: value

Template Helpers

Define common patterns in _helpers.tpl:

{{- define "myapp.labels" -}}
helm.sh/chart: {{ .Chart.Name }}-{{ .Chart.Version | replace "+" "_" }}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
{{- end }}

Schema Validation

Create values.schema.json:

{
  "$schema": "https://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "replicaCount": {
      "type": "integer",
      "minimum": 1,
      "description": "Number of replicas"
    }
  }
}

Best Practices

1. Reference Helm Chart Best Practices
2. Use helpers for reusable patterns
3. Provide sensible security defaults
4. Include comprehensive values documentation
5. Add values.schema.json for IDE support
6. All changes must pass pre-commit checks with prek run --all-files

Labels & Annotations

# ✓ GOOD: Standard Kubernetes labels
metadata:
  labels:
    app.kubernetes.io/name: {{ include "myapp.name" . }}
    app.kubernetes.io/instance: {{ .Release.Name }}
    app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
    app.kubernetes.io/managed-by: {{ .Release.Service }}
    helm.sh/chart: {{ include "myapp.chart" . }}

# ❌ BAD: Non-standard labels
metadata:
  labels:
    app: myapp
    version: v1

Versioning Strategy

Semantic Versioning for Charts

MAJOR.MINOR.PATCH

MAJOR: Breaking changes (incompatible values schema changes)
MINOR: New features (backward compatible)
PATCH: Bug fixes (backward compatible)

Version Bump Guidelines

Chart.yaml Version Management

# Chart version (your release)
version: 2.1.0

# App version (upstream application)
appVersion: "3.5.2"

Dependency Management

Adding Dependencies

# Chart.yaml
dependencies:
  - name: postgresql
    version: "12.x.x" # Use range for flexibility
    repository: https://charts.bitnami.com/bitnami
    condition: postgresql.enabled

Dependency Commands

# Update dependencies
helm dependency update mychart/

# Build dependencies (download to charts/)
helm dependency build mychart/

# List dependencies
helm dependency list mychart/

Chart.lock Management

# Chart.lock (auto-generated, commit to git)
dependencies:
  - name: postgresql
    repository: https://charts.bitnami.com/bitnami
    version: 12.1.6
digest: sha256:abc123...
generated: "2024-01-15T10:30:00Z"

Dependency Version Ranges

# Exact version
version: "12.1.6"

# Patch range (12.1.x)
version: "~12.1.0"

# Minor range (12.x.x)
version: "^12.0.0"

# Greater than
version: ">=12.0.0"

# Range
version: ">=12.0.0 <13.0.0"

Import Values from Dependencies

dependencies:
  - name: postgresql
    version: "12.x.x"
    repository: https://charts.bitnami.com/bitnami
    import-values:
      - child: primary.service
        parent: database
      # Or import all
      - child: null
        parent: postgresql

Upgrade Strategies

Non-Breaking Upgrades

# Add new fields with defaults
newFeature:
  enabled: false # Default to off for existing users

Breaking Changes

# 1. Deprecate in MINOR release
# values.yaml
legacyField: ""  # @deprecated Use newField instead

# 2. Add migration helper
{{- if .Values.legacyField }}
{{- fail "legacyField is deprecated, please use newField" }}
{{- end }}

# 3. Remove in MAJOR release

Upgrade Testing

# Test upgrade from previous version
helm upgrade myrelease mychart/ \
  --dry-run \
  --debug \
  -f old-values.yaml

# Diff changes
helm diff upgrade myrelease mychart/ -f values.yaml

Testing

How Helm Tests Work

1. Define test pods in templates/ with helm.sh/hook: test annotation
2. Install chart with helm install or helm upgrade
3. Run tests with helm test RELEASE_NAME
4. Helm creates pods, executes them, reports results

Test passes: Pod exits with code 0 Test fails: Pod exits with non-zero code

Test Annotations

Test Analysis: What to Test

Test Categories

Basic Test Pod Structure

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-test-connectivity"
  annotations:
    helm.sh/hook: test-success
    helm.sh/hook-delete-policy: before-hook-creation,hook-succeeded
spec:
  containers:
    - name: test
      image: curlimages/curl:8.7.1
      command:
        - sh
        - -c
        - |
          set -e
          curl -f http://myapp-service:8080/health
  restartPolicy: Never

Best practices:

• Use restartPolicy: Never
• Use lightweight images (curlimages/curl, busybox, alpine)
• One test pod tests one thing well
• Exit code 0 = pass, non-zero = fail
• Pin images to specific versions, never use latest

Common test images:

• curlimages/curl:8.7.1 - HTTP endpoint checks
• busybox:1.36 - Basic shell utilities
• bitnami/kubectl:1.29 - Kubernetes API queries
• postgres:16-alpine - Database connectivity

Test Examples

Service Connectivity Test

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-api-test"
  annotations:
    helm.sh/hook: test-success
    helm.sh/hook-delete-policy: before-hook-creation,hook-succeeded
spec:
  containers:
    - name: api-test
      image: curlimages/curl:8.7.1
      command:
        - sh
        - -c
        - |
          set -e
          # Test main endpoint
          curl -f http://{{ .Release.Name }}-service:8080/health || exit 1
          # Verify response content
          curl -s http://{{ .Release.Name }}-service:8080/health | grep -q "status.*ok" || exit 1
          {{- if .Values.auth.enabled }}
          # Test authenticated endpoint
          curl -f http://{{ .Release.Name }}-service:8080/secure \
            -H "Authorization: Bearer {{ .Values.auth.testToken }}" || exit 1
          {{- end }}
  restartPolicy: Never

Configuration Validation Test

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-config-test"
  annotations:
    helm.sh/hook: test-success
spec:
  containers:
  - name: config-test
    image: busybox:1.36
    command:
    - sh
    - -c
    - |
      set -e
      test -f /app/config.yaml || exit 1
      grep -q "logLevel: {{ .Values.logLevel }}" /app/config.yaml || exit 1
      grep -q "database:" /app/config.yaml || exit 1
  volumeMounts:
  - name: config
    mountPath: /app/config.yaml
    subPath: config.yaml
  volumes:
  - name: config
    configMap:
      name: {{ include "myapp.fullname" . }}-config
  restartPolicy: Never

Deployment Readiness Test

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-readiness-test"
  annotations:
    helm.sh/hook: test-success
spec:
  serviceAccountName: {{ include "myapp.fullname" . }}-test-sa
  containers:
  - name: kubectl-test
    image: bitnami/kubectl:1.29
    command:
    - sh
    - -c
    - |
      set -e
      kubectl get deployment {{ .Release.Name }} -n {{ .Release.Namespace }} -o json | \
        jq -e '.status.readyReplicas == {{ .Values.replicaCount }}' || exit 1
  restartPolicy: Never

Database Connection Test

apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-db-test"
  annotations:
    helm.sh/hook: test-success
spec:
  containers:
    - name: db-test
      image: postgres:16-alpine
      command:
        - sh
        - -c
        - |
          set -e
          nc -zv {{ .Values.database.host }} {{ .Values.database.port }} || exit 1
          PGPASSWORD={{ .Values.database.password }} \
          psql -h {{ .Values.database.host }} -p {{ .Values.database.port }} \
                -U {{ .Values.database.user }} -d {{ .Values.database.name }} \
                -c "SELECT 1;" || exit 1
  restartPolicy: Never

Test Organization

mychart/
├── templates/
│   ├── tests/
│   │   ├── test-service-connectivity.yaml
│   │   ├── test-config-validation.yaml
│   │   └── test-readiness.yaml
│   ├── deployment.yaml
│   └── service.yaml

Conditional Testing

Enable/disable tests globally:

{{- if .Values.tests.enabled }}
apiVersion: v1
kind: Pod
metadata:
  name: "{{ .Release.Name }}-test"
  annotations:
    helm.sh/hook: test-success
spec:
  # ...
{{- end }}

In values.yaml:

tests:
  enabled: true

Test specific configurations:

{{- if .Values.metrics.enabled }}
# metrics test
{{- end }}

Test Execution Order

Use helm.sh/hook-weight (lower runs first):

# Test 1: Run first
metadata:
  annotations:
    helm.sh/hook-weight: "-5"

---
# Test 2: Run second
metadata:
  annotations:
    helm.sh/hook-weight: "0"

Running and Debugging

# Run tests
helm test my-release
helm test my-release --logs
helm test my-release --timeout 10m
helm test my-release -n my-namespace

# Debugging
kubectl get pods -n namespace -l helm.sh/hook=test
kubectl logs my-release-test-connectivity -n namespace
kubectl describe pod my-release-test-connectivity -n namespace

Test Design Considerations

Test Independence

Each test should verify one thing well:

# Good: Single focused test
metadata:
  name: "{{ .Release.Name }}-test-health"

# Avoid: Tests multiple unrelated things
metadata:
  name: "{{ .Release.Name }}-test-everything"

Resource Management

Set limits to prevent exhaustion:

spec:
  containers:
    - name: test
      image: curlimages/curl:8.7.1
      resources:
        requests:
          cpu: 100m
          memory: 64Mi
        limits:
          cpu: 200m
          memory: 128Mi

Cleanup Policies

For debugging:

metadata:
  annotations:
    helm.sh/hook-delete-policy: never

Error Handling

Provide clear failure messages:

command:
  - sh
  - -c
  - |
    set -e
    if ! curl -f http://service:8080/health; then
      echo "ERROR: Service health check failed"
      echo "Troubleshooting: kubectl get svc, kubectl logs -l app=myapp"
      exit 1
    fi

Security

Use least privilege RBAC:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: {{ include "myapp.fullname" . }}-test-sa
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: {{ include "myapp.fullname" . }}-test-role
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: {{ include "myapp.fullname" . }}-test-binding
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: {{ include "myapp.fullname" . }}-test-role
subjects:
- kind: ServiceAccount
  name: {{ include "myapp.fullname" . }}-test-sa

Don't embed secrets:

# Avoid
command:
  ["curl", "-H", "Authorization: Bearer super-secret-key", "http://service/"]

# Better
env:
  - name: TEST_TOKEN
    valueFrom:
      secretKeyRef:
        name: test-credentials
        key: token

Common Test Failures

Review & Quality Assurance

Review Checklist

Structure & Organization

• Standard directory structure followed
• Chart.yaml has required fields (apiVersion, name, version)
• README.md exists and is complete
• NOTES.txt provides useful post-install information
• .helmignore excludes unnecessary files
• Templates organized logically

Values Design

• values.yaml has sensible defaults
• All values documented with comments
• values.schema.json validates inputs
• No hardcoded values in templates
• Sensitive values use secrets, not configmaps

Security

• Pod security context defined
• Container security context defined
• Service account with minimal permissions
• Network policies included (if applicable)
• No privileged containers by default
• Resource limits defined

Quality

• Templates pass helm lint
• Unit tests exist and pass
• Labels follow Kubernetes conventions
• Proper use of helpers (_helpers.tpl)
• Consistent naming conventions

Security Review

Pod Security Checklist

# REQUIRED security settings
podSecurityContext:
  runAsNonRoot: true # ✓ Never run as root
  fsGroup: 1000 # ✓ Set filesystem group
  seccompProfile:
    type: RuntimeDefault # ✓ Use seccomp

securityContext:
  allowPrivilegeEscalation: false # ✓ Block privilege escalation
  readOnlyRootFilesystem: true # ✓ Immutable container
  runAsNonRoot: true # ✓ Non-root user
  runAsUser: 1000 # ✓ Specific UID
  capabilities:
    drop:
      - ALL # ✓ Drop all capabilities

Security Anti-Patterns

# ❌ BAD: Privileged container
securityContext:
  privileged: true

# ❌ BAD: Running as root
securityContext:
  runAsUser: 0

# ❌ BAD: Writable root filesystem
securityContext:
  readOnlyRootFilesystem: false

# ❌ BAD: Host namespaces
hostNetwork: true
hostPID: true
hostIPC: true

# ❌ BAD: Dangerous volume mounts
volumes:
  - name: host
    hostPath:
      path: /

# ❌ BAD: Secrets in environment variables (prefer mounted secrets)
env:
  - name: DB_PASSWORD
    value: "hardcoded-password"

# ❌ BAD: No resource limits
resources: {}

RBAC Review

# ✓ GOOD: Minimal permissions
rules:
- apiGroups: [""]
  resources: ["configmaps"]
  verbs: ["get", "list", "watch"]
  resourceNames: ["my-config"]  # Even better: specific resources

# ❌ BAD: Overly permissive
rules:
- apiGroups: ["*"]
  resources: ["*"]
  verbs: ["*"]

# ❌ BAD: Cluster-wide access when namespace-scoped sufficient
kind: ClusterRole  # Should be Role if namespace-scoped

Image Security

# ✓ GOOD: Specific tag
image:
  repository: myapp
  tag: "v1.2.3"  # Specific version

# ❌ BAD: Latest tag
image:
  repository: myapp
  tag: "latest"  # Mutable, unpredictable

# ✓ GOOD: Digest pinning for critical apps
image:
  repository: myapp@sha256:abc123...

Automated Review Tools

# Basic linting
helm lint mychart/

# Strict mode
helm lint mychart/ --strict

# With values
helm lint mychart/ -f values-production.yaml


# Best practices
helm template myrelease mychart/ | polaris audit --audit-path -

# Deprecated APIs
helm template myrelease mychart/ | pluto detect -

# NSA security framework
helm template myrelease mychart/ | kubescape scan framework nsa -

Code Review Comments

Severity Levels

Example Review Comments

🔴 **Critical: Security - Privileged Container**
The container is running as privileged which grants full host access.

```yaml
# Current
securityContext:
  privileged: true

# Suggested
securityContext:
  privileged: false
  allowPrivilegeEscalation: false

🟠 Major: Missing Resource Limits No resource limits defined. This can lead to resource starvation.

# Add to values.yaml
resources:
  limits:
    cpu: 500m
    memory: 512Mi
  requests:
    cpu: 100m
    memory: 128Mi

🟡 Minor: Use nindent instead of indent nindent handles newlines automatically and is more reliable.

# Current
{{ toYaml .Values.labels | indent 4 }}

# Suggested
{{- toYaml .Values.labels | nindent 4 }}

🔵 Suggestion: Consider using a helper This pattern is repeated in multiple templates. Consider extracting to _helpers.tpl.

---

## CI/CD Integration

### GitHub Actions Workflow

```yaml
name: Helm Chart CI

on:
  push:
    paths:
      - "charts/**"
  pull_request:
    paths:
      - "charts/**"

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: azure/setup-helm@v3
      - name: Lint charts
        run: helm lint charts/*

  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: azure/setup-helm@v3
      - name: Install helm-unittest
        run: helm plugin install https://github.com/helm-unittest/helm-unittest
      - name: Run tests
        run: helm unittest charts/*

  template:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: azure/setup-helm@v3
      - name: Template charts
        run: |
          for chart in charts/*; do
            helm template test $chart --debug
          done

  release:
    needs: [lint, test, template]
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Package and push
        run: |
          helm package charts/*
          # Push to registry

Chart Releaser (cr)

# Package and upload to GitHub releases
cr package charts/mychart
cr upload --owner org --git-repo charts
cr index --owner org --git-repo charts --push

Documentation

README Template

# MyApp Helm Chart

![Version: 1.0.0](https://img.shields.io/badge/Version-1.0.0-informational)
![AppVersion: 2.3.1](https://img.shields.io/badge/AppVersion-2.3.1-informational)

## Description

A Helm chart for deploying MyApp on Kubernetes.

## Prerequisites

- Kubernetes 1.23+
- Helm 3.10+
- PV provisioner (if persistence enabled)

## Installing

```bash
helm repo add myrepo https://charts.example.com
helm install myrelease myrepo/myapp
```

## Configuration

| Parameter          | Description        | Default                |
| ------------------ | ------------------ | ---------------------- |
| `replicaCount`     | Number of replicas | `1`                    |
| `image.repository` | Image repository   | `myapp`                |
| `image.tag`        | Image tag          | `""` (uses appVersion) |

## Upgrading

### From 1.x to 2.x

Breaking changes:

- `image.name` renamed to `image.repository`
- Minimum Kubernetes version is now 1.23

Migration:

```yaml
# Old (1.x)
image:
  name: myapp

# New (2.x)
image:
  repository: myapp
  tag: "2.3.4"
```

Auto-Generate Docs (helm-docs)

helm-docs --chart-search-root=charts/