# Abstract Component

_Atmos Design Pattern_

The **Abstract Component** pattern marks a component as a blueprint that cannot be deployed directly. Abstract components serve as base configurations that other components inherit from, preventing accidental deployment of incomplete or template configurations.

## Use-cases

Use the **Abstract Component** pattern when:

- You have base components that should never be deployed on their own

- You want to prevent accidental `atmos terraform apply` on template configurations

- You need a clear distinction between "blueprints" and "deployable" components

## How It Works

Set `metadata.type: abstract` to mark a component as non-deployable:

**File:** `stacks/catalog/vpc/defaults.yaml`

```yaml
components:
  terraform:
    vpc/defaults:
      metadata:
        type: abstract  # Cannot be deployed directly
      vars:
        enabled: true
        nat_gateway_enabled: true
        max_subnet_count: 3
```

Components that inherit from abstract components are deployable by default:

**File:** `stacks/deploy/prod.yaml`

```yaml
import:
  - catalog/vpc/defaults

components:
  terraform:
    vpc:
      metadata:
        component: vpc
        inherits:
          - vpc/defaults  # Inherits from abstract component
      vars:
        name: prod-vpc
```

## Error on Deploy Attempt

If you try to deploy an abstract component:

```shell
atmos terraform apply vpc/defaults -s prod
```

Atmos returns an error:

```console
abstract component 'vpc/defaults' cannot be provisioned since it's explicitly
prohibited from being deployed by 'metadata.type: abstract' attribute
```

## When to Use Abstract vs Real

| Type | Use When |
|------|----------|
| `abstract` | Base configurations, templates, shared defaults |
| `real` (default) | Deployable components in actual stacks |

:::tip
If you don't specify `metadata.type`, the component defaults to `real` and can be deployed.
:::

## Related Patterns

- [Component Inheritance](/design-patterns/inheritance-patterns/component-inheritance) - How components inherit from abstract bases
- [Multiple Component Instances](/design-patterns/inheritance-patterns/multiple-component-instances) - Deploy multiple instances from one abstract base
- [Component Catalog](/design-patterns/component-catalog) - Organize abstract and real components

## References

- [Component Inheritance](/howto/inheritance)