Real applications rarely stand alone — they often need a cache, a database, or a message queue. Rather than write and maintain those charts yourself, Helm lets you pull in an existing chart as a dependency. In this chapter we add a Redis cache to Book Info as a subchart, using the CloudPirates Redis chart.

Declaring a dependency

Dependencies are listed in Chart.yaml under dependencies:

apiVersion: v2
name: book-info
version: 0.2.0
appVersion: "1.20.3"

dependencies:
  - name: redis
    version: "0.33.0"
    repository: oci://registry-1.docker.io/cloudpirates
    condition: redis.enabled

Each dependency has:

• name — the chart name in the repository.
• version — a SemVer constraint (0.33.0, ~0.33.0, >=0.33.0 <1.0.0, …).
• repository — where to fetch it (an HTTP repo or an oci:// registry).
• condition — an optional value that toggles the dependency on or off.

Fetching dependencies

Helm downloads dependencies into the charts/ folder and writes a Chart.lock:

helm dependency update ./book-info

Saving 1 charts
Downloading redis from repo oci://registry-1.docker.io/cloudpirates
Deleting outdated charts

Chart.lock pins the exact resolved versions — commit it to Git so every teammate and every CI run gets identical builds. Later, helm dependency build installs precisely what the lock file records.

Configuring a subchart

A subchart reads its values from a key named after the chart in your parent values.yaml. So to configure the Redis subchart, nest everything under redis::

# values.yaml (parent)
redis:
  enabled: true
  architecture: standalone
  auth:
    enabled: true
    password: "change-me"

Everything under redis: is handed to the Redis chart as its top-level values. The enabled flag pairs with the condition: redis.enabled we set in Chart.yaml, so you can switch Redis off in environments that don’t need it:

# values-dev.yaml
redis:
  enabled: false

Global values

Sometimes parent and subcharts need to share a value — an image registry or an environment label. Anything under the special global: key is visible to every chart, parent and children alike:

global:
  imageRegistry: my-registry.example.com

A subchart reads it as .Values.global.imageRegistry.

Inspecting the dependency tree

helm dependency list ./book-info

NAME   VERSION  REPOSITORY                               STATUS
redis  0.33.0   oci://registry-1.docker.io/cloudpirates  ok

Render everything together to confirm the Redis objects appear alongside Book Info:

helm template book-info ./book-info | grep -E 'kind: (StatefulSet|Service)'

When to use a subchart vs. a separate release

A subchart is the right choice when the dependency is part of your app’s lifecycle — installed, upgraded, and deleted together with it. If a component is shared across many apps or owned by another team, keep it as its own release instead and just point your app at its Service. Coupling everything into one giant umbrella chart makes upgrades riskier, so lean toward smaller, focused charts.

The umbrella chart with the Redis dependency is in 07-dependencies-and-subcharts.

With dependencies we can compose applications from reusable parts. In the next chapter we’ll look at the day-2 story — safely upgrading, rolling back, and hooking into a release’s lifecycle.