Go Templates & Values

🔥 Vibe Prompt

"Helm template with conditionals, loops, and named templates. Generate multi-environment configs."

Template Functions

# Values
{{ .Values.replicaCount }}
{{ .Release.Name }}
{{ .Chart.Name }}
{{ .Release.Namespace }}

# Conditionals
{{- if .Values.ingress.enabled }}
  ingress:
    host: {{ .Values.ingress.host | quote }}
{{- end }}

# Loops
{{- range .Values.envSecrets }}
  - name: {{ .name }}
    valueFrom:
      secretKeyRef:
        name: {{ .secretName }}
        key: {{ .secretKey }}
{{- end }}

# Default values
{{ .Values.image.tag | default "latest" | quote }}

# Named templates (from _helpers.tpl)
{{- define "myapp.labels" }}
app: {{ .Chart.Name }}
release: {{ .Release.Name }}
{{- end }}

# Use it
labels:
  {{- include "myapp.labels" . | nindent 4 }}

Multi-Environment

# Override values per env
helm install prod ./myapp -f values/prod.yaml

diff --git a/values/dev.yaml b/values/prod.yaml
--- replicaCount: 1
+++ replicaCount: 5
--- resources: {limits: {cpu: "0.5"}}
+++ resources: {limits: {cpu: "2", memory: "2Gi"}}

Advanced Functions

# Type coercion
{{ .Values.replicaCount | int }}
{{ .Values.duration | toString }}

# String operations
{{ .Values.name | upper | lower | title }}
{{ .Values.host | trimSuffix ".com" }}

# JSON/YAML
{{ .Values.config | toJson }}
{{ .Values.config | toYaml }}

Best Practices

Always use {{- to trim whitespace
Use _helpers.tpl for reusable snippets
Validate with helm lint and helm template
Document values.yaml with comments

Chapter Summary

Understand core concepts and principles
Master implementation methods and techniques
Familiar with common issues and solutions
Able to apply in real projects

Implementation Example

Basic Example

# This section provides a complete implementation example

Steps

Setup: Configure development environment
Data: Prepare required data
Implementation: Build core functionality
Testing: Verify correctness
Optimization: Improve performance

Common Errors

| Error Type | Cause | Solution | |------------|-------|----------| | Compilation | Syntax | Check code syntax | | Runtime | Environment | Verify dependencies installed | | Logic | Algorithm | Step-by-step debugging | | Performance | Efficiency | Use profilers |

Code Example

import sys

def main():
    print("Hello, World!")

if __name__ == "__main__":
    main()

References

Official documentation
API reference
Open source examples
Community discussions

Template Functions and Pipelines

Helm provides many built-in template functions and supports pipelining (chaining functions with |).

String Functions

| Function | Purpose | Example | |----------|---------|--------| | upper | Convert to uppercase | {{ .Values.name | upper }} | | lower | Convert to lowercase | {{ .Values.name | lower }} | | title | Title case | {{ "hello world" | title }} | | trim | Remove whitespace | {{ .Values.name | trim }} | | quote | Wrap in double quotes | {{ .Values.name | quote }} | | nospace | Remove all spaces | {{ .Values.name | nospace }} | | repeat | Repeat string N times | {{ .Values.name | repeat 3 }} |

Default Values

# In values.yaml
image:
  repository: nginx
  # tag: 1.25  <-- this field is optional

# In deployment.yaml
  image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default "latest" }}"

Required Values (Fail if Missing)

# Fails installation if .Values.database.url is missing
  - name: DATABASE_URL
    value: {{ required "database.url is required!" .Values.database.url }}

Flow Control

If-Else

{{- if .Values.persistence.enabled }}
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: {{ include "myapp.fullname" . }}
spec:
  accessModes:
    - {{ .Values.persistence.accessMode | default "ReadWriteOnce" | quote }}
  resources:
    requests:
      storage: {{ .Values.persistence.size | default "8Gi" }}
{{- end }}

With (Scope Change)

# Without "with"
  env:
    - name: NODE_ENV
      value: {{ .Values.env.nodeEnv }}
    - name: PORT
      value: {{ .Values.env.port | quote }}

# With "with" — shorter!
{{- with .Values.env }}
  env:
    - name: NODE_ENV
      value: {{ .nodeEnv }}
    - name: PORT
      value: {{ .port | quote }}
{{- end }}

Range (Loop)

# values.yaml
envVars:
  - name: NODE_ENV
    value: production
  - name: LOG_LEVEL
    value: info

# template
  env:
  {{- range .Values.envVars }n    - name: {{ .name }}
      value: {{ .value | quote }}
  {{- end }}

Values Precedence

Helm values come from multiple sources with a clear priority order:

| Priority | Source | Example | |----------|--------|--------| | 1 (highest) | --set flags | --set image.tag=v2 | | 2 | --values file | -f custom-values.yaml | | 3 | Parent chart values | From umbrella chart | | 4 | Chart's values.yaml | Default values in chart |

Subchart Values

Access subchart values with the global prefix or direct values.

Global Values

# Parent values.yaml
global:
  imageRegistry: my-registry.io
  database:
    host: primary-db.example.com

# Subchart accesses it as:
# {{ .Values.global.database.host }}

Exporting Values

# Subchart values.yaml
exports:
  data:
    url: http://my-service:8080

# Parent chart accesses:
# {{ .Values.subchartName.exports.data.url }}

Summary

Go templates in Helm provide powerful functions, flow control, and a flexible values system. Mastering these patterns makes charts maintainable and reusable.

Key takeaways:

Use default for optional values with sensible defaults |
Use required to fail fast on missing critical values |
Pipelines chain functions: {{ val | upper | quote }} |
if/else controls conditional resource creation |
with changes the scope (shortens dot references) |
range iterates over lists and maps |
--set overrides have highest precedence |
Global values propagate to all subcharts |

What's Next: Dependencies and Subcharts

The next chapter covers managing chart dependencies and subcharts.