title: How you Reference the function ARN of a Function (Lambda) in serverless.yml file?
body: <p><strong>Considering this lambda function on a serverless.yml file:</strong></p>
  
  <pre><code>functions:
    s3toEc2Lambda:
      handler: s3toec2lambda.S3toEc2Lambda
      name: "${self:service}-s3toEc2Lambda"
      role: S3toEc2LambdaRole
  </code></pre>
  
  <p><strong>And considering this SNS created on resources section: Does someone knows how to inform the Sns ARN Endpoint from the lambda function s3toEc2Lambda ?</strong></p>
  
  <pre><code>resources:
    Resources:
      WordpressFrontEndSnsS3toEc2:
        Type: AWS::SNS::Topic
        Properties:
          TopicName: "wordpress-front-end-s3-ec2"
  
      WordpressFrontEndSnsS3toEc2Lambda:
        Type: AWS::SNS::Subscription
        Properties:
          Endpoint: { "Fn::GetAtt": ["s3toEc2Lambda", "Arn" ] }                    &lt;------ HERE    &lt;------
          #Endpoint: ${self:functions.s3toEc2Lambda}                               &lt;------ OR HERE &lt;------
          #Endpoint: { "Fn::GetAtt": ["${self:functions.s3toEc2Lambda}", "Arn" ] } &lt;------ OR HERE &lt;------
          Protocol: lambda
          TopicArn: !Ref 'WordpressFrontEndSnsS3toEc2'
  </code></pre>
  
  <p><strong>For me always appear a error message like this: "Template error: instance of Fn::GetAtt references undefined resource s3toEc2Lambda"</strong></p>
  
  <p>Thank You !</p>