Name of the resource

AWS::CloudFormation::CustomResource

Resource name

No response

Reference Link

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/crpg-ref-requesttypes-delete.html

Details

I am observing behavior in Custom Resources that I have been unable to find anywhere else on either the web or AWS documentation. It involves the presence of a value in PhysicalResourceId that I suspect CloudFormation is generating on-the-fly under specific rollback scenarios.

This behavior only surfaces during the rollback of a stack creation operation in which a custom resource began to be provisioned prior to the rollback-inducing event.

Here's the sequence of events from CloudFormation's perspective:

1. CFN begins creating resources, one of which is an AWS::CloudFormation::CustomResource
2. While the custom resource is still CREATE_IN_PROGRESS, another resource fails to be created
3. CFN begins to roll back the stack creation
4. CFN emits a CREATE_FAILED event (with reason Resource creation cancelled) for the custom resource
5. CFN begins deleting the custom resource (event: DELETE_IN_PROGRESS)

On the custom resource side, I've observed the following:

• I get a Delete request for the custom resource (makes sense)
• The Delete request is sent before the Create request response was ever received by CFN (makes less sense)
• The Delete request contains a physical resource ID that I never set on the resource. It's always a concatenation of a) the stack name, b) the logical ID, and c) some random hash. For example: MYSTACK-LOGICALID-B36FTLCJN97H

I've been unable to find any documentation explaining the pseudo-physical resource ID that CloudFormation includes on Delete requests sent due to a stack rollback (if that is indeed the intended scenario where this occurs). All documentation implies that the PhysicalResourceId field is always a value that was provided by the custom resource provider after a successful Create request.