How to refer a derived variable in CloudFormation? - amazon-web-services

Question

I am looking for small help in CloudFormation and could not find help from documentation or may be not searching the question in right way.
Here is the question.
I am getting availability zones for the environment from mappings as follows.
"AvailabilityZone": {
"Fn::Select": [
"1",
{
"Fn::FindInMap": [
"Environment",
{
"Ref": "EnvType"
},
"AvailabilityZones"
]
}
]
}
I need to use the AZ name in my volume naming convention. How could refer the derived variable "AvailabilityZone" again.?
Currently i am doing this.
{
"Key": "Name",
"Value": {
"Fn::Join": [
"-",
[
{
"Ref": "NamePrefix"
},
{
"Ref": "EnvType"
},
"myconstant",
{
"Fn::Select": [
"2",
{
"Fn::Split": [
"-",
{
"Fn::Select": [
"1",
{
"Fn::FindInMap": [
"Environment",
{
"Ref": "EnvType"
},
"AvailabilityZones"
]
}
]
}
]
}
]
}
]
]
}
}
I am doing the same code twice.
How can i re-use the derived variable here.?

Answer 1

Unfortunately, the short answer is you can't. Hopefully someday AWS supports variables in CloudFormation.
There are some hacks that might be of interest. Emphasis on hack!
Use a CloudFormation pre-processor that does what you want (eg, Troposphere)
Use a Custom Resource that outputs the value, then use GetAtt to refer to the value. (http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-custom-resources.html)
Use the AWS::Include transform to refer to a template snippet in S3 (http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/create-reusable-transform-function-snippets-and-add-to-your-template-with-aws-include-transform.html), in that case you're not really using variables, off course.