CloudFormation Route53 - Update an existing RecordSet - aws-cloudformation

Question

I am trying to write a BLUE/GREEN CFT that tears down and rebuilds the EC2 Instances, ELB and Update the Route53 record Alias with this updated DNS name of this ELB.
If the Alias Record DOESNT exist, I'm able to create the Alias Record Set correctly after the EC2 instances are created and the ELB attaches these instances. But If the recordset exists with the old ELB DNS Name, the CFT is failing with "Alias RecordSet exists". Naturally - am looking to UPDATE this record with the updated ELB DNS name on running the full CFT. Any suggestions?
"HostRecord" : {
"Type" : "AWS::Route53::RecordSet",
"Properties" : {
"HostedZoneName" : "REDACTED",
"Comment" : "Updates the ELB DNS name into Route 54 recordset.",
"Name" : "REDACTED",
"Type" : "A",
"AliasTarget" : {
"DNSName" : { "Fn::GetAtt" : [ "ESClusterELB" , "DNSName" ] },
"HostedZoneId" : { "Fn::GetAtt" : [ "ESClusterELB" , "CanonicalHostedZoneNameID" ] }
}

Answer 1

Managing a single resource (such as a RecordSet) from 2 different CloudFormation stacks is not supported.
I have a few recommandations for your use-case:
I recommend you manage the record independently from the templates that you're using for blue/green. Once green is created/updated and you want your record to resolve for the green ELB, you can just update the stack that govern the RecordSet, setting it to the appropriate alias.
Using the same base as the first suggestion. You could automate this using the SNS notification triggered by CloudFormation when a stack is created/updated. Using this in conjunction with a Lambda you could dynamically update the stack that controls the RecordSet.
You could create a custom resource that solely serve the purpose of updating the record set to the wanted alias.

Answer 2

Your problem seems to revolve around creating two CloudFormation stacks with conflicting resources which cannot coexist. One way to approach this is to always create the alias records in such a way that they can coexist.
An approach that should allow that is to create a weighted routing type. Set the weight of the recordset in both stack instances to 1 and set the recordset ID to "blue" or "green" respectively.
Now you should be able to deploy both CFN stacks side by side without conflict. If the blue stackinstance is active and the green is not, all dns responses will return the blue alias. When you then activate green, it will create a recordset alongside the blue and should start to take about half of the traffic. Now if you deactivate the blue stack, green will take over all traffic.
This does mean you need to disable blue to test green in complete isolation, which is perhaps a little inconvenient and may slow down rollback. You could have a two-phase deployment, where you keep the weights as stack parameters, then once green is deployed with weight=1, redeploy blue with weight=0 to take it out of dns without tearing it down. If green is bad, you can deactivate it and blue with weight zero should take over.
Weighted routing is only one routing type option, you could also look at multi-value answers, failover or even geolocation.

Answer 3

Just to get creative. You could also set a parameter that sets a condition in your CF that will execute execute different portions for your Route53 For example, having a condition to of your CF. CREATE, DELETE, IGNORE. Something like that.