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Chapter 10.3 - Advanced Templates and Hooks

Learning Objectives​

By the end of this chapter, you will be able to:

  • Use advanced Go template functions
  • Implement conditions and loops
  • Use Helm Hooks
  • Manage dependencies between resources
  • Create reusable templates
  • Optimize Charts

Introduction​

Helm templates allow you to create dynamic and reusable Kubernetes configurations. Hooks allow you to execute actions at specific points in the lifecycle.

Advanced Template Functions​

Conditions​

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

Loops​

{{- range .Values.env }}
- name: {{ .name }}
  value: {{ .value }}
{{- end }}

Default Values​

replicas: {{ .Values.replicaCount | default 3 }}
image: {{ .Values.image.repository | default "nginx" }}

Concatenation​

name: {{ printf "%s-%s" .Release.Name .Chart.Name }}

Include​

{{- include "my-chart.labels" . | nindent 4 }}

Helm Hooks​

Hooks allow you to execute Jobs or Pods at specific points.

Hook Types​

  • pre-install: Before installation
  • post-install: After installation
  • pre-upgrade: Before upgrade
  • post-upgrade: After upgrade
  • pre-delete: Before deletion
  • post-delete: After deletion
  • pre-rollback: Before rollback
  • post-rollback: After rollback

Example: Pre-install Hook​

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ .Release.Name }}-pre-install
  annotations:
    "helm.sh/hook": pre-install
    "helm.sh/hook-weight": "-5"
    "helm.sh/hook-delete-policy": before-hook-creation
spec:
  template:
    spec:
      containers:
      - name: pre-install
        image: busybox:1.35
        command: ["/bin/sh", "-c", "echo 'Pre-install hook'"]
      restartPolicy: Never

Example: Post-install Hook​

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ .Release.Name }}-post-install
  annotations:
    "helm.sh/hook": post-install
    "helm.sh/hook-weight": "5"
spec:
  template:
    spec:
      containers:
      - name: post-install
        image: busybox:1.35
        command: ["/bin/sh", "-c", "echo 'Post-install hook'"]
      restartPolicy: Never

Hook Annotations​

hook-weight​

Controls execution order:

"helm.sh/hook-weight": "-5"  # Executed first
"helm.sh/hook-weight": "5"   # Executed last

hook-delete-policy​

When to delete the Hook:

  • before-hook-creation: Before creating a new hook
  • hook-succeeded: If the hook succeeds
  • hook-failed: If the hook fails
"helm.sh/hook-delete-policy": "before-hook-creation,hook-succeeded"

Complete Example: Database Migration​

Pre-upgrade Hook: Backup​

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ .Release.Name }}-pre-upgrade-backup
  annotations:
    "helm.sh/hook": pre-upgrade
    "helm.sh/hook-weight": "-10"
spec:
  template:
    spec:
      containers:
      - name: backup
        image: postgres:14
        command:
        - /bin/bash
        - -c
        - |
          pg_dump -h {{ .Release.Name }}-postgres mydb > /backup/backup-$(date +%Y%m%d).sql
          aws s3 cp /backup/backup-$(date +%Y%m%d).sql s3://backups/
        env:
        - name: PGPASSWORD
          valueFrom:
            secretKeyRef:
              name: {{ .Release.Name }}-postgres-secret
              key: password
        volumeMounts:
        - name: backup
          mountPath: /backup
      volumes:
      - name: backup
        emptyDir: {}
      restartPolicy: Never

Post-upgrade Hook: Migration​

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ .Release.Name }}-post-upgrade-migrate
  annotations:
    "helm.sh/hook": post-upgrade
    "helm.sh/hook-weight": "10"
spec:
  template:
    spec:
      containers:
      - name: migrate
        image: my-app:{{ .Values.appVersion }}
        command: ["/app/migrate.sh"]
        env:
        - name: DATABASE_URL
          value: postgresql://postgres:5432/mydb
      restartPolicy: OnFailure

Reusable Templates​

Advanced _helpers.tpl​

{{/*
Common labels
*/}}
{{- define "my-chart.labels" -}}
app.kubernetes.io/name: {{ include "my-chart.name" . }}
app.kubernetes.io/instance: {{ .Release.Name }}
app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
{{- end }}

{{/*
Selector labels
*/}}
{{- define "my-chart.selectorLabels" -}}
app.kubernetes.io/name: {{ include "my-chart.name" . }}
app.kubernetes.io/instance: {{ .Release.Name }}
{{- end }}

{{/*
Chart name
*/}}
{{- define "my-chart.name" -}}
{{- default .Chart.Name .Values.nameOverride | trunc 63 | trimSuffix "-" }}
{{- end }}

{{/*
Full name
*/}}
{{- define "my-chart.fullname" -}}
{{- if .Values.fullnameOverride }}
{{- .Values.fullnameOverride | trunc 63 | trimSuffix "-" }}
{{- else }}
{{- $name := default .Chart.Name .Values.nameOverride }}
{{- if contains $name .Release.Name }}
{{- .Release.Name | trunc 63 | trimSuffix "-" }}
{{- else }}
{{- printf "%s-%s" .Release.Name $name | trunc 63 | trimSuffix "-" }}
{{- end }}
{{- end }}
{{- end }}

Best Practices​

1. Use Helpers​

Create reusable helpers in _helpers.tpl.

2. Appropriate Conditions​

Use conditions to make templates flexible.

3. Judicious Hooks​

Use hooks only when necessary (migrations, backups).

4. Documentation​

Document hooks and their purpose.

5. Testing​

Test hooks with --dry-run.

Summary​

In this chapter, you learned:

Advanced functions: Conditions, loops, default values, concatenation
Hooks: Pre/post install/upgrade/delete/rollback
Annotations: hook-weight, hook-delete-policy
Use cases: Migrations, backups, initialization
Reusable templates: Helpers in _helpers.tpl
Best practices: Helpers, conditions, judicious hooks, testing

Next Steps​

Module 11: Monitoring and Observability
Lab 10.4: Helmfile and Multi-environments

Chapter created on: December 2024