> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nuon.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Component Overrides

> Override Helm values and Terraform variables on a per-install basis, without changing your app config.

Component overrides let you customize a single install's [Helm](/guides/helm-chart-components) values or
[Terraform](/guides/terraform-components) variables without touching your app config. They're defined per-install, so one
customer can get a different chart configuration or a different set of Terraform variables while every other install
keeps the app defaults.

Use them for one-off customizations that don't belong in your app config, such as bumping a replica count for a customer
under load, pinning a region for a specific install, or applying a temporary support tweak, where authoring a new input
or editing the shared component would be overkill.

<Note>
  Overrides are configured on the **install**, not the component. The component's app config stays the source of truth for
  every other install.
</Note>

## Configuring overrides

Overrides live in the install config under a `[components.<name>]` block, keyed by the component's name. Each component
supports exactly one override field, matching its type:

| Component type   | Field         | Format               | Behavior                                                                      |
| ---------------- | ------------- | -------------------- | ----------------------------------------------------------------------------- |
| Helm chart       | `helm_values` | YAML                 | Deep-merges over the component's app-config values; wins on overlapping keys. |
| Terraform module | `tf_vars`     | `.tfvars` (HCL/JSON) | Appended as the final, highest-precedence `-var-file`.                        |

### Helm values

`helm_values` is a raw YAML string that deep-merges over the Helm component's app-config values. Overlapping keys win,
and keys you don't mention are left untouched.

```toml install.toml theme={null}
name = "customer-acme"

[components.clickhouse]
helm_values = """
replicas: 3
resources:
  limits:
    memory: 4Gi
"""
```

### Terraform variables

`tf_vars` is a raw `.tfvars` string (HCL or JSON) appended as the final `-var-file` at deploy time, so it wins over the
component's `vars` map and any `var_files`. The variables must already be declared in the module.

```toml install.toml theme={null}
name = "customer-acme"

[components.vpc]
tf_vars = """
cidr = "10.0.0.0/16"
"""
```

You can set overrides for multiple components in the same install config:

```toml install.toml theme={null}
name = "customer-acme"

[components.vpc]
tf_vars = """
cidr = "10.0.0.0/16"
"""

[components.clickhouse]
helm_values = """
replicas: 3
"""
```

## Precedence

Overrides are the highest-precedence layer. For Helm, they deep-merge on top of the app-config values and win on any
key they set. For Terraform, they're applied as the last `-var-file`, so they win over the module's `vars` and
`var_files`.

## Applying overrides

Overrides are applied by syncing the install config with the CLI:

```bash theme={null}
nuon installs sync --file install.toml --app-id <your-app-id> --yes
```

The CLI validates override syntax locally before making any API calls: `helm_values` must be valid YAML and `tf_vars`
must be valid HCL. Because an override changes a component's deploy config, syncing it triggers a redeploy of the
affected component.

## Clearing an override

To revert a component to its app-config values, remove its `[components.<name>]` block (or the individual field) from the
install config and sync again. The next sync clears the override and redeploys the component with the app defaults.