# Hooks
<a name="sam-property-function-hooks"></a>

Validation Lambda functions that are run before and after traffic shifting.

**Note**  
The Lambda functions referenced in this property configure the `CodeDeployLambdaAliasUpdate` object of the resulting [AWS::Lambda::Alias](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-alias.html) resource. For more information, see [CodeDeployLambdaAliasUpdate Policy](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatepolicy.html#cfn-attributes-updatepolicy-codedeploylambdaaliasupdate) in the *AWS CloudFormation User Guide*.

## Syntax
<a name="sam-property-function-hooks-syntax"></a>

To declare this entity in your AWS Serverless Application Model (AWS SAM) template, use the following syntax.

### YAML
<a name="sam-property-function-hooks-syntax.yaml"></a>

```
  [PostTraffic](#sam-function-hooks-posttraffic): {{String}}
  [PreTraffic](#sam-function-hooks-pretraffic): {{String}}
```

## Properties
<a name="sam-property-function-hooks-properties"></a>

 `PostTraffic`   <a name="sam-function-hooks-posttraffic"></a>
Lambda function that is run after traffic shifting.  
*Type*: String  
*Required*: No  
*CloudFormation compatibility*: This property is unique to AWS SAM and doesn't have an CloudFormation equivalent.

 `PreTraffic`   <a name="sam-function-hooks-pretraffic"></a>
Lambda function that is run before traffic shifting.  
*Type*: String  
*Required*: No  
*CloudFormation compatibility*: This property is unique to AWS SAM and doesn't have an CloudFormation equivalent.

## Examples
<a name="sam-property-function-hooks--examples"></a>

### Hooks
<a name="sam-property-function-hooks--examples--hooks"></a>

Example hook functions

#### YAML
<a name="sam-property-function-hooks--examples--hooks--yaml"></a>

```
Hooks:
  PreTraffic:
    Ref: PreTrafficLambdaFunction
  PostTraffic:
    Ref: PostTrafficLambdaFunction
```

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for AWS Serverless Application Model. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query serverless-application-model` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).