Run Custom resource whenever i update my CFN Stack

Question

I have a custom resource used to get the API key from API gateway and send it as a header to Cloudfront. When i am creating a stack my custom:resource is triggering since it is creating logical ID for first time. But when i update the stack(i.e Changing the API KEY name) Then the API key resource of type AWS::ApiGateway::ApiKey will create a new Logical ID when in turn create a new API key, At this point my custom:resource is not invoking since it has same same logical ID because of this my cloudfront is having old API Key rather than new one.

Is there a way to invoke my custom:resource everytime a update happened to my stack? As a workaround i am changing the Logical Id of custom:resource to trigger it whenever i am updating a resource in my stack. But this is little difficult since logicalId is shared as a reference to many resources.

BTW my custom resource is attached to a lambda function. I even tried changing the Version field and also tried adding values to properties field (i.e.Stackname,parameters etc) but still it is not invoking.

{
   "AWSTemplateFormatVersion" : "2010-09-09",
   "Resources" : {
      "MyFrontEndTest" : {
         "Type": "Custom::PingTester",
         "Version" : "1.0", -->Even changed the version to 2.0 
         "Properties" : {
            "ServiceToken": "arn:aws:lambda:us-east-1:*****",
            "InputparameterName" :  "MYvalue" -->Added this field
         }
      }
   }

Thanks Any help is appreciated

Answer 1

One trick to get the custom resource to execute a lambda when the stack is updated is to configure the custom resource to pass all stack parameters to the lambda function. If any parameters change on stack update, the custom resource will change and trigger the lambda. Just ignore the unneeded keys in the lambda event data. This won't do anything for the scenario when just the template is updated.