Working with Subcharts

1. Adding Subcharts to Chart

Field	Description	Example
dependencies	List of subcharts (dependencies) to include in the main chart	`[{ name: "nginx", version: "1.2.3", repository: "https://charts.example.com" }]`

Example: Adding a subchart to Chart.yaml

apiVersion: v2
name: my-app
version: 1.0.0
dependencies:
  - name: nginx
    version: "1.2.3"
    repository: "https://charts.example.com"

Note: The repository field can be a URL or alias defined in repositories.yaml.

Warning: Helm does not support nested subcharts (subcharts depending on other subcharts). All dependencies must be direct children of the root chart.

2. Declaring Subchart Dependencies

Field	Description	Example
dependencies	List of subchart dependencies	`[{ name: "nginx", version: "1.2.3", repository: "@stable" }]`

Example: Declaring a subchart dependency

dependencies:
  - name: nginx
    version: 1.2.3
    repository: "@stable"

Note: The repository field can be a URL or alias defined in repositories.yaml.

3. Overriding Subchart Values

Property	Values	Description
subchartName.valueName	`newValue`	Override a specific value in a subchart using the dot notation
subchartName.nested.value	`overriddenValue`	Override nested values in subcharts

Example: Overriding subchart values in `values.yaml`

subchart1:
  image:
    tag: "v2.0"
  replicas: 3

subchart2:
  config:
    debug: true

Note: Values overridden in values.yaml take precedence over defaults defined in the subchart's own values.yaml.

4. Using Global Values

Property	Description	Usage
global.imagePullSecrets	Global image pull secrets for all charts	`global.imagePullSecrets: [{ name: "my-secret" }]`
global.storageClass	Default storage class for all charts	`global.storageClass: "fast"`
global.namespace	Namespace to deploy all charts into	`global.namespace: "production"`

Example: Setting global values in a values.yaml file

global:
  imagePullSecrets:
    - name: my-secret
  storageClass: fast
  namespace: production

myapp:
  replicas: 3

Example: Accessing global values in a template

{{ .Values.global.storageClass }}
{{ .Values.global.namespace }}

Note: Global values are merged into the chart's values during template rendering, allowing for centralized configuration across subcharts.

5. Importing Subchart Values

Property	Description	Example
importValues	Specifies which values from the parent chart are imported into the subchart	`[ { "child": "redis", "parent": "database" } ]`

Example: Importing Values from Parent Chart

importValues:
  - child: "redis"
    parent: "database"

Note: The importValues feature is available in Helm v3.10+.

6. Conditionally Enabling Subcharts

Field	Description	Example
enabled	Boolean flag to conditionally enable or disable a subchart	`true` or `false`
name	Name of the subchart to be enabled/disabled	`nginx-ingress`

Example: Enabling subchart based on condition

subchart1:
  enabled: {{ .Values.subchart1.enabled }}
  name: "subchart1"

Example: Using values to control subchart enabling

subchart1:
  enabled: {{ .Values.enableSubchart1 }}

Note: The enabled field in the values file controls whether a subchart is installed. If false, Helm skips installing that subchart even if it's listed in requirements.yaml.

Warning: If a subchart is disabled, its values are not merged into the release, and any dependencies it has will not be resolved.

7. Using Subchart Tags

Tag	Description	Usage
appVersion	Version of the application being deployed	`"1.2.3"`
version	Version of the chart itself	`"1.0.0"`
annotations	Metadata annotations for the chart	`{"helm.sh/chart": "my-chart-1.0.0"}`

Example: Setting Chart Tags in values.yaml

appVersion: "1.2.3"
version: "1.0.0"
annotations:
  helm.sh/chart: "my-chart-1.0.0"

Note: The appVersion is used to track the version of the application being deployed, while version refers to the chart version.

8. Accessing Parent Values

When a subchart accesses values from its parent chart, it uses the parent keyword in its templates and values files.

Property	Description	Usage
parent.values	Reference to parent chart's values	`{{ parent.values.key }}`

Example: Accessing Parent Values in Subchart Template

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ include &#34;my-subchart.fullname&#34; . }}
data:
  config.yaml: |
    parentValue: {{ parent.values.someKey }}

Note: The parent.values syntax is only available in Helm 3.10+.

Property	Description	Usage
_helpers.tpl	Template files in this namespace are available to all charts and subcharts	Used for shared templates like labels, annotations, or common configurations
include	Function to include templates from other charts or subcharts	Used in chart templates to render shared components

Example: Using _helpers.tpl

{{- define &#34;mychart.labels&#34; -}}
app: {{ include &#34;mychart.name&#34; . }}
version: {{ include &#34;mychart.version&#34; . }}
{{- end -}}

Example: Including a shared template

metadata:
  labels:
    {{- include &#34;mychart.labels&#34; . | nindent 4 }}

10. Managing Subchart Versions

Field	Description	Example
version	Version of the subchart, used for dependency management	`1.2.3`
alias	Alias to use for the subchart in the parent chart	`my-subchart`
repository	Repository URL where the subchart is located	`https://example.com/charts`
condition	Condition to enable or disable the subchart	`subchart.enabled`
tags	Tags to associate with the subchart for filtering	`web,api`

Example: Defining subchart dependencies

dependencies:
- name: nginx
  version: 1.2.3
  repository: https://kubernetes-charts.storage.googleapis.com/
  condition: nginx.enabled
  tags:
    - web
    - frontend

Note: Helm uses semantic versioning for subchart versions. When updating a subchart, ensure that the new version is compatible with your chart's configuration.

Warning: If a subchart's version is not specified in Chart.yaml, Helm will use the latest available version from the repository, which may introduce breaking changes.