Feature Request: Add support to specify a SNS topic that belongs to a different region

[DaichiUeura]

Hello,

I tried to set a SNS topic existed in a different region as a trigger like below. However CloudFormation said "Invalid parameter: TopicArn". Is this a current limitation or something like that?

...
Parameters:
  EventTopicArn:
    Type: String
Resources:
  SampleProcessor:
    Type: 'AWS::Serverless::Function'
    Properties:
...
      Events:
        SampleSNS:
          Type: SNS
          Properties:
            Topic: !Ref EventTopicArn
...

[jolexa]

@DaichiUeura - I am seeking the same answer, may you tell me why you closed this? Was there a resolution? Thanks!

[DaichiUeura]

@jolexa The reason why I closed this is that this seems to be not a SAM file issue. Here is the explanation from AWS support.

This error happens when a SNS Topic and a SNS Subscription are created in different regions(i.e. Both needs to exist in a same region). If there is a SNS Topic declaration at Events property in a SAM file, a SNS Subscription is created in the region where a stack is created.

To avoid the issue, we need;

1. Do not refer a SNS Topic existed in a different region from SAM.
2. Add a Lambda::Permission resource into SAM for the Lambda function to be able to be invoked from the SNS Topic.
3. Create a SNS Subscription where the SNS Topic exists.

[jolexa]

Ok, thanks. I understand and was afraid that was the case. I think that SAM should be able to parse the region from the SNS TopicArn and be able to implicitly do the correct thing. That may be tricky with the cloudformation architecture. Would you mind 1) Updating this issue's title to say "Feature Request:" and 2) re-open the issue so that we can get a SAM maintainer's opinion/attention someday?

[DaichiUeura]

@jolexa Done ;)

[sanathkr]

Appreciate the feature request. SAM can't do much here because it can only meddle with resources we create in the template. Outside resources are pretty much a blackbox when it comes to SAM

I created pull request to add description in specification #312

[evantorrie]

This should be possible now since Cloudformation has added a Region parameter to the SNS Topic subscription format, viz. https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-sns-subscription.html

[evantorrie]

@DaichiUeura Can we reopen this? Given that it's now supported in CloudFormation?