I have an existing AWS CloudFormation stack that has an Amazon SNS topic resource, and I want to subscribe the Amazon SQS queue in a different stack to subscribe to the SNS topic from the other stack. How do I do that?
If both the SNS topic and SQS queue are in the same stack, the process is simpler; see Using an AWS CloudFormation Template to Create a Topic that Sends Messages to Amazon SQS Queues. However, if the SNS topic and SQS queue are in two separate stacks, this cause a race condition.
To avoid this, use CloudFormation custom resources:
1. In the SNS stack, use the ARN of the SNS topic as an output, similar to the following:
"Outputs" : {
"SnsTopicName" : {
"Value" : {"Ref" : "SNStopic"}
}
}
2. Create a Lambda function resource that describes the SNS stack and retrieve the values from the outputs of the SNS stack.
3. In the SQS stack, create a custom resource that gets the SNS ARN from the SNS stack, similar to the following (note: the example preassumes that the logical name you chose in the last preceding step was “LambdaReturnSNSARN”):
"GetSNSTopicName" : {
"Type": "Custom::GetSNSTopicName",
"Properties": {
"ServiceToken": {"Fn::GetAtt": ["LambdaReturnSNSArn", "Arn"]},
"StackName": {"Ref": "SnsStackName"}
}
},
4. In the same SQS stack, create another custom resource that subscribes the SQS queue to the SNS topic, similar to the following:
"SubscribeSNS" : {
"Type": "Custom::SubscribeSNS",
"Version" : "1.0",
"Properties" : {
"ServiceToken" : {"Fn::GetAtt": ["LambdaSubscribeSNS", "Arn"]},
"SNSarn" : {"Fn::GetAtt": ["GetSNSTopicName", "SnsTopicName"]},
"SQSarn" : {"Fn::GetAtt": ["MySQS", "Arn"]}
}
},
5. Create a Lambda function resource that uses the parameter values that are passed to "SNSarn" and "SQSarn" and subscribes the SQS queue to the SNS topic from another stack.
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Published: 2016-08-24
Updated: 2017-05-04
