Helm values and templating — Go template patterns in production

Helm values are the chart’s configuration. This lesson walks the values.yaml structure, Go template patterns, values merging, the —set vs -f trade-off, value validation, and the operational discipline.

The values structure

# values.yaml
replicaCount: 3
image:
  repository: myapp
  tag: "1.0.0"
  pullPolicy: IfNotPresent
service:
  type: ClusterIP
  port: 80
ingress:
  enabled: false
  className: nginx
  annotations: {}
  hosts:
    - host: myapp.example.com
      paths:
        - path: /
          pathType: Prefix
resources:
  requests:
    cpu: 100m
    memory: 128Mi
  limits:
    cpu: 500m
    memory: 512Mi
autoscaling:
  enabled: false
  minReplicas: 1
  maxReplicas: 100
  targetCPUUtilizationPercentage: 80
nodeSelector: {}
tolerations: []
affinity: {}

The values structure:

• Nested maps for related values (image.repository, image.tag).
• Lists for arrays (ingress.hosts).
• Booleans for feature toggles (ingress.enabled, autoscaling.enabled).
• Defaults for sensible production values.

The discipline is to structure values logically; the template uses dot notation ({{ .Values.image.tag }}) to access them.

Go template patterns

# Conditional
{{- if .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: {{ include "mychart.fullname" . }}
spec:
  rules:
  {{- range .Values.ingress.hosts }}
    - host: {{ .host | quote }}
      http:
        paths:
        {{- range .paths }}
          - path: {{ .path }}
            pathType: {{ .pathType }}
            backend:
              service:
                name: {{ include "mychart.fullname" $ }}
                port:
                  number: {{ $.Values.service.port }}
        {{- end }}
  {{- end }}
{{- end }}

Common patterns:

• Conditional. {{- if .Values.X }} … {{- end }} renders the block only if the condition is true.
• Loop. {{- range .Values.X }} … {{- end }} iterates over a list.
• Variable capture. {{ $ := . }} captures the root context; use $ to reference it inside a range.
• Function call. {{ .host | quote }} pipes the value to the quote function.
• YAML rendering. {{- toYaml .Values.resources | nindent 12 }} converts a value to YAML and indents it.

Values merging

flowchart LR
    A[values.yaml defaults] --> D[Final values]
    B[-f prod-values.yaml] --> D
    C[--set replicaCount=5] --> D

The merge order (later overrides earlier):

1. Chart’s values.yaml (defaults).
2. Files passed with -f (in order).
3. Values passed with --set (highest priority).

This allows a base values file plus environment- specific overrides:

helm install myrelease mychart/ \
  -f values.yaml \
  -f values-prod.yaml \
  --set image.tag=2.0.0

The --set image.tag=2.0.0 overrides anything in the files.

—set vs -f

flowchart LR
    A[--set replicaCount=5] --> B[Hard to review]
    A --> C[Not in version control]
    A --> D[Best for ad-hoc overrides]
    E[-f values-prod.yaml] --> F[Easy to review]
    E --> G[In version control]
    E --> H[Best for production]

The trade-off:

• —set. Quick; convenient for ad-hoc overrides and tests. Hard to review; not in version control.
• -f. Reviewable; version-controlled. Best for production.

Value validation (values.schema.json)

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["image", "service"],
  "properties": {
    "image": {
      "type": "object",
      "required": ["repository", "tag"],
      "properties": {
        "repository": {"type": "string"},
        "tag": {"type": "string"}
      }
    },
    "replicaCount": {"type": "integer", "minimum": 1},
    "service": {
      "type": "object",
      "properties": {
        "port": {"type": "integer", "minimum": 1, "maximum": 65535}
      }
    }
  }
}

A JSON schema in values.schema.json validates the values during install/upgrade. Required fields, type checks, and range constraints prevent common errors.

helm install myrelease mychart/ -f values-prod.yaml
# Error: values don't satisfy schema

Quiz

The operational discipline

Helm values in production rest on five non-negotiable elements:

• Values files in version control. Production values are in Git (or another VCS).
• Pin chart and app versions. Never use latest.
• Validate with schema. values.schema.json catches errors before apply.
• Use -f for production. Reserve —set for development.
• Document the values. Comment the values file; explain non-obvious values.

Helm values are production configuration. Treat them with the same rigour as Kubernetes manifests.