# Mixins

The `mixins` key in `component.yaml` allows you to download additional files and overlay them on the vendored component. This is useful for adding or replacing files that are not part of the original component source.

## Schema

```yaml
spec:
  mixins:
    - uri: https://raw.githubusercontent.com/cloudposse/terraform-null-label/0.25.0/exports/context.tf
      filename: context.tf
    - uri: https://raw.githubusercontent.com/cloudposse/terraform-aws-components/{{.Version}}/modules/datadog-agent/introspection.mixin.tf
      version: 1.398.0
      filename: introspection.mixin.tf
```

## Attributes

- **`uri`**

  The URL to download the mixin file from. Supports the same protocols as the `source.uri` attribute: HTTP, HTTPS, Git, S3, GCP, and OCI.

  Golang templates are supported in the URI. If `version` is provided, `{{.Version}}` will be replaced with the version value.
- **`version`**

  Optional version to substitute into `{{.Version}}` placeholders in the `uri`. Each mixin can have its own version independent of the main source version.
- **`filename`**

  The filename to save the downloaded file as in the component directory. This allows you to rename files or ensure they have the correct name.

  Mixins override files from `source` with the same `filename` (e.g. `context.tf` will override `context.tf` from the `source`).

## How Mixins Work

Mixins are processed **after** the main source is downloaded. All mixins are processed in the order they are declared in the list.

This means:

1. The component source files are downloaded first
2. Each mixin file is downloaded and placed in the component directory
3. If a mixin has the same filename as a source file, the mixin **overwrites** the source file

## Example: Replacing context.tf

A common use case is to replace the `context.tf` file from a component with a newer version:

```yaml
apiVersion: atmos/v1
kind: ComponentVendorConfig
metadata:
  name: vpc-flow-logs-bucket-vendor-config
  description: Source and mixins config for vendoring of 'vpc-flow-logs-bucket' component
spec:
  source:
    uri: github.com/cloudposse/terraform-aws-components.git//modules/vpc-flow-logs-bucket?ref={{.Version}}
    version: 1.398.0
    included_paths:
      - "**/*.tf"
      - "**/*.tfvars"
      - "**/*.md"
    # Exclude context.tf since we'll replace it with a mixin
    excluded_paths:
      - "**/context.tf"

  mixins:
    # Download a newer version of context.tf
    - uri: https://raw.githubusercontent.com/cloudposse/terraform-null-label/0.25.0/exports/context.tf
      filename: context.tf
```

## Example: Adding Multiple Mixins

You can add multiple mixin files to a component:

```yaml
spec:
  source:
    uri: github.com/cloudposse/terraform-aws-components.git//modules/vpc?ref={{.Version}}
    version: 1.398.0

  mixins:
    # Add context.tf
    - uri: https://raw.githubusercontent.com/cloudposse/terraform-null-label/0.25.0/exports/context.tf
      filename: context.tf

    # Add an introspection mixin from another component
    - uri: https://raw.githubusercontent.com/cloudposse/terraform-aws-components/{{.Version}}/modules/datadog-agent/introspection.mixin.tf
      version: 1.398.0
      filename: introspection.mixin.tf

    # Add a custom providers configuration
    - uri: https://example.com/terraform/providers.tf
      filename: providers.tf
```

:::tip
When using mixins, consider excluding the files you intend to replace in the `excluded_paths` of the source configuration. This makes your intent clear and avoids downloading files that will be overwritten.
:::