Creating Helm Charts

Chart Anatomy

mychart/
├── Chart.yaml        # apiVersion: v2, name, version (chart semver), appVersion
├── values.yaml       # default configuration
├── templates/        # rendered into manifests
│   ├── deployment.yaml
│   ├── _helpers.tpl  # named templates, not rendered alone
│   └── NOTES.txt     # printed after helm install
├── charts/           # packaged subchart dependencies
└── .helmignore

Helm renders every file under templates/ through Go's template engine, concatenates the output, and submits it as YAML. Files starting with _ define named templates only. Chart.yaml version tracks the chart itself; appVersion tracks the packaged application — bump them independently.

Template Syntax That Works

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ include "mychart.fullname" . }}
  labels:
    {{- toYaml .Chart.Labels | nindent 4 }}
spec:
  replicas: {{ .Values.replicaCount }}
  {{- with .Values.nodeSelector }}
  nodeSelector:
    {{- toYaml . | nindent 4 }}
  {{- end }}
  {{- if eq .Values.mode "ha" }}
  strategy: { type: Recreate }
  {{- end }}

Context is everything: . is the root data inside {{ }}; with rebinds . to the block's value (so {{ . }} inside is the list itself). Helpers in _helpers.tpl avoid duplication: {{ include "mychart.fullname" . }}, built-ins .Release.Name, .Release.Namespace, .Capabilities.APIVersions.Has, plus required "replicaCount is mandatory" .Values.x.

Pitfalls and Interview Angles

Indentation bugs are the number-one failure: toYaml output must go through | nindent 4 (or hand-built indentation). Off-by-two spaces yields "error converting YAML" at apply time — catch it earlier with helm template | kubeconform.

Lost context in helpers. A helper invoked without . cannot see values; always pass the context: include "x" ..

Overlong names. Deployment and Service names must match selectors and stay ≤63 chars — the standard fullname helper truncates.

Unquoted numbers. Ports like 8080 rendered as 8080 are fine, but version-like values (1.10) become floats — wrap with quote.

Interview angle: describe your validation pipeline (helm lint → helm template → schema validation → diff) and explain how with changes ..