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snsSubscription

A Lambda function which implements a Custom Resource for Cloud Formation that creates a SNS subscription to an already existing SNS topic. This is useful if you create the AWS::SNS::Topic and subscriptions in different cloudformation stacks, ie using stackDependency.

For example if you want to achieve the following:

  • One service producer is reading from Kinesis and publishing some events to a SNS topic.
  • Another service consumer wants to consume these events.
  • Each service is deployed using its own cloudformation stack.
  • The producer should not be aware of the consumers.

Solution:

  • Create the AWS::SNS::Topic in the producer stack
  • Use a Custom::stackDependency and Custom::SnsSubscription in the consumer stack

Installation

Create a Role with ./create-role.sh. This creates a new stack with the appropriate permissions for the function.

Deploy the lambda function with ./deploy-lambda.sh.

Cloud Formation Usage

Use the function inside your Cloud Formation template by declaring a custom resource, Custom::SnsSubscription. It takes the same parameters as the SNS.subscribe function:

  • TopicArn
  • Protocol
  • Endpoint

The only output is the SubscriptionArn which can be referred with Fn:GetAtt, like this "Fn::GetAtt": ["MySubscription", "SubscriptionArn"].

See test-stack.template for example usage.