# Resource attributes supported by AWS SAM
<a name="sam-specification-resource-attributes"></a>

Resource attributes are attributes that you can add to AWS SAM and CloudFormation resources to control additional behaviors and relationships. For more information about resource attributes, see [Resource Attribute Reference](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-product-attribute-reference.html) in the *AWS CloudFormation User Guide*.

AWS SAM support a subset of resource attributes that are defined by CloudFormation. Of the supported resource attributes, some are copied to only the base generated CloudFormation resource of the corresponding AWS SAM resource, and some are copied to all generated CloudFormation resources resulting from the corresponding AWS SAM resource. For more information about CloudFormation resources generated from corresponding AWS SAM resources, see [Generated CloudFormation resources for AWS SAM](sam-specification-generated-resources.md).

The following table summarizes resource attribute support by AWS SAM, subject to the [Exceptions](#sam-specification-resource-attributes-exceptions) listed below.


| Resource attributes | Destination generated resource(s) | 
| --- | --- | 
|  ** [DependsOn](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-dependson.html) ** ** [Metadata](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-metadata.html) **1, 2  |  Base CloudFormation generated resource only. For information about the mapping between AWS SAM resources and base CloudFormation resources, see [Generated CloudFormation resource scenarios](sam-specification-generated-resources.md#sam-specification-generated-resources-scenarios).  | 
| ** [Condition](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html) ** ** [DeletionPolicy](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-deletionpolicy.html) ** ** [UpdateReplacePolicy](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatereplacepolicy.html) **  |  All generated CloudFormation resources from the corresponding AWS SAM resource. For information about scenarios for generated CloudFormation resources, see [Generated CloudFormation resource scenarios](sam-specification-generated-resources.md#sam-specification-generated-resources-scenarios).  | 

**Notes:**

1. For more information about using the `Metadata` resource attribute with the `AWS::Serverless::Function` resource type, see [Building Lambda functions with custom runtimes in AWS SAM](building-custom-runtimes.md).

1. For more information about using the `Metadata` resource attribute with the `AWS::Serverless::LayerVersion` resource type, see [Building Lambda layers in AWS SAM](building-layers.md).

## Exceptions
<a name="sam-specification-resource-attributes-exceptions"></a>

There are a number of exceptions to the resource attribute rules described previously:
+ For `AWS::Lambda::LayerVersion`, the AWS SAM-only custom field `RetentionPolicy` sets the `DeletionPolicy` for the generated CloudFormation resources. This has a higher precedence than `DeletionPolicy` itself. If neither is set, then by default `DeletionPolicy` is set to `Retain`.
+ For `AWS::Lambda::Version`, if `DeletionPolicy` is not specified, the default is `Retain`.
+ For the scenario where `DeploymentPreferences` is specified for a serverless function, resource attributes are not copied to the following generated CloudFormation resources:
  + `AWS::CodeDeploy::Application`
  + `AWS::CodeDeploy::DeploymentGroup`
  + The `AWS::IAM::Role` named `CodeDeployServiceRole` that is created for this scenario
+ If your AWS SAM template contains multiple functions with API event sources that are implicitly created, then the functions will share the generated `AWS::ApiGateway::RestApi` resource. In this scenario, if the functions have different resource attributes, then for the generated `AWS::ApiGateway::RestApi` resource, AWS SAM copies the resource attributes according to the following prioritized lists:
  + `UpdateReplacePolicy`:

    1. `Retain`

    1. `Snapshot`

    1. `Delete`
  + `DeletionPolicy`:

    1. `Retain`

    1. `Delete`