Lesson 14 — Dependencies & Subcharts

Lesson 14 · Slide 1

Dependencies & Subcharts

Composing complex applications from reusable chart building blocks.

Declaring dependencies in Chart.yaml
helm dependency update & the charts/ directory
Subchart value overrides & global values
Conditions and tags for toggling dependencies
Library charts & import-values
Version ranges & OCI-based dependencies

Lesson 14 · Slide 2

Declaring Dependencies in Chart.yaml

apiVersion: v2
name: myapp
version: 1.0.0

dependencies:
  - name: postgresql
    version: "13.2.24"
    repository: "https://charts.bitnami.com/bitnami"
    condition: postgresql.enabled
    tags:
      - database

  - name: redis
    version: "18.6.1"
    repository: "https://charts.bitnami.com/bitnami"
    condition: redis.enabled
    tags:
      - cache

  - name: common
    version: "2.x.x"
    repository: "https://charts.bitnami.com/bitnami"
    tags:
      - infra

Notes: Each dependency has a name, version, and repository. The condition and tags fields control whether the dependency is installed.

Lesson 14 · Slide 3

helm dependency update & charts/

# Download dependencies into charts/ directory
$ helm dependency update ./myapp
Saving 3 charts
Downloading postgresql from repo https://charts.bitnami.com/bitnami
Downloading redis from repo https://charts.bitnami.com/bitnami
Downloading common from repo https://charts.bitnami.com/bitnami
Deleting outdated charts

# Rebuild from Chart.lock (reproducible builds)
$ helm dependency build ./myapp

helm dependency update — resolves versions, downloads .tgz archives, generates Chart.lock
helm dependency build — uses existing Chart.lock for deterministic builds
All dependency archives land in charts/

Notes: Add charts/*.tgz to .gitignore and commit Chart.lock for reproducible CI/CD builds.

Lesson 14 · Slide 4

Subchart Value Overrides

Parent values.yaml

# Override postgresql subchart values
postgresql:
  enabled: true
  auth:
    username: myapp
    database: myapp_db
    existingSecret: myapp-db-secret
  primary:
    persistence:
      size: 20Gi

# Override redis subchart values
redis:
  enabled: true
  architecture: standalone
  auth:
    enabled: false
  master:
    persistence:
      size: 5Gi

Global values

global:
  storageClass: "gp3"
  imageRegistry: "registry.example.com"
  imagePullSecrets:
    - name: registry-creds

Global values are accessible from every chart and subchart via .Values.global.*.

Use globals for cross-cutting concerns: registry, storage class, domain names.

Notes: Parent chart values are keyed by the dependency name. A key postgresql: in the parent's values.yaml passes values down to the postgresql subchart.

Lesson 14 · Slide 5

Conditions & Tags

# Chart.yaml
dependencies:
  - name: postgresql
    condition: postgresql.enabled    # single boolean check
    tags:
      - database                     # group toggle
  - name: mysql
    condition: mysql.enabled
    tags:
      - database

# values.yaml
postgresql:
  enabled: true
mysql:
  enabled: false

tags:
  database: true    # enables all charts tagged "database"
  cache: false      # disables all charts tagged "cache"

condition takes precedence over tags
Tags enable/disable groups of dependencies at once
Override at install time: --set tags.database=false

Lesson 14 · Slide 6

Library Charts & import-values

Library Chart

# Chart.yaml of the library
apiVersion: v2
name: mylib
type: library
version: 1.0.0

Library charts provide reusable templates but never deploy resources on their own.

# In parent Chart.yaml
dependencies:
  - name: mylib
    version: "1.x.x"
    repository: "https://..."

import-values

# Chart.yaml
dependencies:
  - name: postgresql
    version: "13.2.24"
    repository: "https://..."
    import-values:
      - child: primary.service
        parent: dbService
      - child: auth
        parent: dbAuth

Import specific subchart values into the parent scope.

child = path in subchart, parent = key in parent values.

Notes: Use type: library for shared helpers (labels, annotations, common templates). They are included via {{ include "mylib.labels" . }} but produce no manifests themselves.

Lesson 14 · Slide 7

Version Ranges & OCI Dependencies

# Semantic version ranges
dependencies:
  - name: redis
    version: "~18.6.0"     # >=18.6.0, <18.7.0  (patch updates only)
    repository: "https://charts.bitnami.com/bitnami"

  - name: postgresql
    version: "^13.2.0"     # >=13.2.0, <14.0.0  (minor + patch updates)
    repository: "https://charts.bitnami.com/bitnami"

  - name: kafka
    version: ">=26.0.0 <27.0.0"  # explicit range
    repository: "https://charts.bitnami.com/bitnami"

# OCI-based dependencies (Helm 3.8+)
dependencies:
  - name: nginx
    version: "15.4.4"
    repository: "oci://registry-1.docker.io/bitnamicharts"

Notes: ~ (tilde) allows patch updates. ^ (caret) allows minor + patch. OCI repos use the oci:// scheme and do not need helm repo add.

Lesson 14 · Slide 8

Summary

Chart.yaml dependencies — name, version, repository, condition, tags
helm dependency update/build — download and lock dependencies
charts/ directory — where dependency archives live
Value overrides — parent keys matching subchart name pass values down
Global values — .Values.global.* accessible everywhere
Conditions & tags — toggle dependencies on/off; condition wins over tags
Library charts — type: library, reusable templates, no resources
import-values — pull subchart values into parent scope
Version ranges — ~, ^, explicit ranges for flexibility
OCI dependencies — oci:// repos, no helm repo add needed

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