可以使用AWS SAM的API Gateway来实现将两个域名映射到同一个函数的目的。在API Gateway上创建一个REST API，并添加两个域名作为API的自定义域名。然后在API Gateway上创建Lambda集成，将其关联到相应的Lambda函数。

以下是一个示例AWS SAM模板，它使用API Gateway将两个域名映射到同一个Lambda函数：

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Resources:
  ApiGatewayApi:
    Type: 'AWS::Serverless::Api'
    Properties:
      StageName: Prod
      DefinitionBody:
        swagger: '2.0'
        info:
          version: '1.0.0'
          title: My API
        schemes:
          - https
        paths:
          /myresource:
            get:
              x-amazon-apigateway-integration:
                type: aws
                uri: !Sub arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaFunction.Arn}/invocations
                httpMethod: POST
                credentials: !GetAtt ApiGatewayRole.Arn
                responses: {}
              produces:
                - application/json
              500:
                description: 'Server Error'
  ApiGatewayDeployment:
    Type: 'AWS::Serverless::Api'
    DependsOn: ApiGatewayApi
    Properties:
      StageName: Prod
  ApiGatewayDomainName1:
    Type: 'AWS::ApiGateway::DomainName'
    Properties:
      DomainName: 'example.com'
      CertificateArn: 'arn:aws:acm:us-east-1:123456789012:certificate/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'
  ApiGatewayDomainName2:
    Type: 'AWS::ApiGateway::DomainName'
    Properties:
      DomainName: 'sub.example.com'
      CertificateArn: 'arn:aws:acm:us-east-1:123456789012:certificate/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'