AWS Copilot - Attach Imported Policy to Task Role - amazon-web-services

Question

I'm trying to use CloudFormation AddOn template in the following scenario:
Service 1
creates an SNS Topic and a Managed Policy that has all the necessary permissions to publish to it. The SNS Topic will collect "Activity" records and then fan them out to multiple subscribers.
A common code library abstracts away the usage of SNS - any applications that need to post activity messages do so without any knowledge that SNS is being used underneath the covers.
Service N needs to publish activity messages using the common code library and needs whatever permissions are necessary.
So service 1 writes the Managed Policy ARN out as an exported output to the AddOn stack like so:
Outputs:
activityPublishPolicy:
Description: "Activity Publish Policy ARN"
Value: !Ref activitySnsTopicPublishPolicy
Export:
Name: !Sub ${App}-${Env}-activity-publish-policy
Then in service N, I was hoping to import the ARN of the publishing policy and get it attached to the task role:
Outputs:
activityPublishAccessPolicy:
Description: "The IAM::ManagedPolicy to attach to the task role."
Value: !ImportValue
'Fn::Sub': '${App}-${Env}-activity-publish-policy'
The ARN is imported just fine and written out to the Cloud Formation stack of Service N; however, the Task Role does not get the Managed Policy attached to it.
I did a quick test to see if adding the policy directly to the AddOn stack would attach and that does indeed work.
Outputs:
activityPublishAccessPolicy:
Description: "The IAM::ManagedPolicy to attach to the task role."
Value: !Ref activityPolicy
This leads me to believe that Copilot only attaches ManagedPolicies to the Task Role that are created in its own AddOn Stack, but that's just a guess.
I'd prefer not to write a new policy in every service to do this, and I'd prefer not to open up the topic policy our whole VPC if possible.
Is there a better way of doing this?
Thanks!

Answer 1

This is because Copilot scans the Addons template to determine the type of the resource you're outputting. There are several "magic" outputs for addons. They are:
Security Groups
Managed Policies
Secrets
To detect these outputs, we scan the template looking for the logical ID of the referenced resource. This means that we don't currently have a way of deriving the resource type of the results of Fn::ImportValue calls, since they don't refer to a logical ID defined in that addons template!
I'm sorry this is causing you problems--it seems like you may need to add the managed policy to the addons stack of each service you want to grant this access to. This is something we might be able to do something about, though, and would love if if you could cut us a Github issue so we can prioritize and gather feedback on a proposal.