1: CloudFormation Intrinsic Functions

Ref

• Returns the value of the specified parameter or resource
• Json: { "Ref" : "logicalName" }
• Yaml: !Ref logicalName

Fn:FindInMap

• It’s a hashmap lookup.
• Find e.g. AMI for a type of instance in a certain region

What are CF intrinsic functions?

• Built-in funcs to dynamically assign values to properties at runtime
• E.g. retrieve public IP of ec2 instance in the stack at runtime

Fn::GetAtt

• Returns value of an attribute from a resource
• JSON: Fn::GetAtt: [logicalNameOfResource, attributeName]

Fn::ImportValue

• Returns value of an output exported by another stack
  • (Cross-stack reference)
• Values are spit out from “output” section of another stack
• JSON: "Fn::ImportValue" : {"Fn::Sub" : ${NetworkStackNameParameter}-SecurityGroupID"}

Fn::Sub

• String substitution builder
• JSON: {"Fn::Sub": ["www.${Domain}", {"Domain": {"Ref": "RootDomainName"}}]}

Fn::Join

• Concatenate strings
• Yaml: !Join [ "/", ["s3://mybucket", !Ref myfolder, "myfile.txt" ] ]
• Result: "s3://mybucket/myFolderValue/myfile.txt"

Condition Funcs

• Boolean operators: And, or, if, not, equals
• If prod: Beefy server, if dev: scrappy box
• Create or not create resources based on conditions