# Subcharts and Dependencies — Helm

Source: https://www.skillbyai.com/en/helm/a-deps

> Declare dependencies, pass values to subcharts and share global values.

## Charts made of charts

A chart declares other charts it needs in the `dependencies` list of `Chart.yaml`, each with a `name`, a `version` range and a `repository` (HTTP repo or `oci://` URL). **`helm dependency update`** downloads them into `charts/` and writes **`Chart.lock`** with exact versions; commit the lock file and use `helm dependency build` in CI to reproduce it. A **`condition`** such as `postgresql.enabled` lets users switch a dependency off (for example, when production uses a managed database), and **`alias`** installs the same chart twice under different names. Configure a subchart from the parent by nesting values under the subchart's name; values under **`global`** are visible to the parent and every subchart as `.Values.global`. A subchart **cannot** read its parent's values. An **umbrella chart** is a parent whose job is mainly to install several subcharts together.

## Parent and subcharts

The parent passes values down by subchart name; global values reach everyone.

![A large parent box at the top with arrows down to three smaller subchart boxes, plus a wide band across all of them representing shared global values.](assets/figures/helm/section-5-map.svg) — Figure 5.1 — An umbrella chart passing values to subcharts.

## Configuring a dependency from the parent

Dev uses the bundled PostgreSQL; production switches it off and points at a managed database.

```yaml
# values.yaml of the parent chart
global:
  imageRegistry: registry.example.com

postgresql:            # passed to the postgresql subchart as its .Values
  enabled: true
  auth:
    database: shop
    existingSecret: shop-db-credentials

# values-prod.yaml
postgresql:
  enabled: false
externalDatabase:
  host: shop-prod.postgres.example.internal

# commands
# helm dependency update ./charts/shop-api   # writes charts/*.tgz and Chart.lock
# helm dependency build  ./charts/shop-api   # in CI: restore exactly what Chart.lock says
```

## Do not let production data depend on a subchart toggle

A stateful subchart such as a database is convenient for dev but risky in production: an accidental `helm uninstall` removes it too. Many teams run production databases outside the app chart, or as a managed service.

**Quiz:** How does a parent chart set the `auth.database` value of a dependency called postgresql?

- [x] In postgresql.auth.database in the parent's values
- [ ] In global.auth.database only
- [ ] By editing the subchart's files in charts/
- [ ] Subcharts cannot be configured

*Answer:* In postgresql.auth.database in the parent's values. Values nested under the subchart's name are passed to that subchart.