SAM Template Event Type - amazon-web-services

Question

How to add an event type as Cloudfront for SAM template for a Lambda function
I have a SAM template where there will be a lambda function and Api gateway as a trigger , Now instead of Api gateway as a Trigger , I need to add an existing CLoudfront Distribution. But I am not finding any such option to do that.
cloudfrontlambda:
Type: AWS::Serverless::Function
Properties:
FunctionName: cloudfrontlambda
Handler: index.handler
Runtime: nodejs8.10
CodeUri: ./Lambda/cloudfrontlambda/
Description: Function is used for validating the id token
MemorySize: 128
Timeout: 30
Role: 'arn:aws:iam::1234567:role/DR_lambda_web_execution'
Events:
--------- ## how to add an Existing cloudfront distribution here

Answer 1

At present there is no event source type for CloudFront distributions within the SAM model [1]. Assuming you are attempting to create an edge lambda function, you will need to attach the function either manually or via the cloudformation template that you used to create the distribution - as it needs to be declared directly against the cloud front distribution. I’ve edited it down for brevity, but for example -
cloudfrontlambda:
Type: AWS::Serverless::Function
Properties:
FunctionName: cloudfrontlambda
Handler: index.handler
Runtime: nodejs8.10
CodeUri: ./Lambda/cloudfrontlambda/
Description: Function is used for validating the id token
MemorySize: 128
Timeout: 30
Role: 'arn:aws:iam::1234567:role/DR_lambda_web_exec’
cloudfrontdistribution:
Type: AWS::CloudFront::Distribution
Properties:
DistributionConfig:
CacheBehaviors:
- LambdaFunctionAssociations:
- EventType: string-value
LambdaFunctionARN: !Sub ‘${cloudfrontlambda.Arn}:${cloudfrontlambda.Version}’
E.g.
Note that your lambda function must be deployed in us-east-1 to work in this way. I can confirm that you can deploy a cloud front distribution via a cloudformation template in another region and still reference lambda functions that are deployed to us-east-1.
Also, you must specify the version of the lambda function within the ARN. The AWS::Lambda::Function cloudformation type does not provide this on its own (requiring an additional AWS::Lambda::Version resource), so this may complicate your CloudFront distribution template if it is not already contained with a SAM template.
[1] https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#event-source-object

Answer 2

Short answer, SNS. Long answer, you can't except for SNS.
You can't add an existing CloudFront resource, because that breaks the mold of CF. This took me a while to wrap my head around too, but essentially a CloudFront template can only create/modify resources within itself. It cannot modify resources outside of its stack. Here are a few links supporting this:
https://github.com/awslabs/serverless-application-model/issues/241
https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#s3 (specifically says existing S3 buckets cannot be an event source)
This last link shows that recently they supported importing resources from other stacks, but the resource must first be deleted from its previous stack before it can be used. I'm not sure about your architecture, but I know for mine that would break things very quickly. https://github.com/awslabs/serverless-application-model/issues/249
The work around is to add Custom Resources (lambdas) to alleviate this impediment. In the last link I sent there is an example of an SNS workaround since this limitation does not apply to SNS.