Flow Control and Named Templates

In the last chapter we learned to read and shape values. Now we add logic: generating resources conditionally, looping to avoid repetition, and factoring out reusable snippets. These are the tools that let one small chart deploy a whole application.

Conditionals: if / else

Render a block only when a condition is true:

{{- if .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ .Release.Name }}
{{- end }}

You can add else and else if too:

type: {{ if .Values.service.external }}LoadBalancer{{ else }}ClusterIP{{ end }}

Helm treats these as false: false, 0, an empty string, an empty list, an empty map, and nil. Everything else is true.

Loops: range

range iterates over a list or a map — perfect for generating N similar resources. Over a list:

env:
{{- range .Values.extraEnv }}
  - name: {{ .name }}
    value: {{ .value | quote }}
{{- end }}

Inside the loop, . (the dot) is rebound to the current item. Over a map you get both key and value:

{{- range $key, $value := .Values.annotations }}
{{ $key }}: {{ $value | quote }}
{{- end }}

The dot and the `$` root

This trips up every beginner, so it’s worth stating clearly: inside a range (or with), the dot . changes to point at the current item. If you still need the top-level context — .Values, .Release, .Chart — use the root object $, which always points at the very top:

{{- range $name, $svc := .Values.services }}
  image: "{{ $.Values.image.registry }}/{{ $svc.repository }}"
{{- end }}

Here $svc is the current service, but $.Values.image reaches back to the global image settings. We’ll rely on exactly this pattern when we template the Book Info app.

Scope: with

with narrows the dot to a sub-object, saving repetition:

{{- with .Values.resources }}
resources:
  requests:
    cpu: {{ .requests.cpu }}
    memory: {{ .requests.memory }}
{{- end }}

Inside the with, . is .Values.resources. Bonus: the block is skipped entirely if resources is empty — a neat way to make optional sections disappear.

Named templates: define and include

Repetition across files (labels, selectors, names) is best factored into named templates in _helpers.tpl. Define one with define:

{{- define "book-info.labels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
{{- end -}}

Then pull it in wherever you need it with include, piping through nindent to get the indentation right:

metadata:
  labels:
    {{- include "book-info.labels" . | nindent 4 }}

Why include and not template? Helm has a template action too, but it can’t be piped into functions like nindent. include returns the rendered text as a string, so it composes with pipelines. Always prefer include.

Notice we pass . as the second argument — that hands the current context to the named template so it can read .Chart, .Release, and so on. Inside a range, you’d pass $ instead to give it the root context.

fail and required — guard rails

You can stop a render with a clear error when a required value is missing:

image: {{ required "image.repository is required!" .Values.image.repository }}

This is far friendlier than shipping a broken manifest to the cluster.

A complete helper file

Putting it together, a typical _helpers.tpl provides a name helper and a labels helper that every resource reuses:

{{- define "book-info.name" -}}
{{ .Chart.Name }}
{{- end -}}

{{- define "book-info.labels" -}}
app.kubernetes.io/name: {{ .Chart.Name }}
app.kubernetes.io/instance: {{ .Release.Name }}
app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
helm.sh/chart: {{ printf "%s-%s" .Chart.Name .Chart.Version }}
{{- end -}}