Table of contents

• Conditions
  • Conditional Intrinsic Functions
    • And
    • Or
    • Equals
    • Not
    • If
      • AWS::NoValue

Conditions

A condition can be used to determine if a resource should be created or not.

Info on Conditions from AWS can be found here

For example, if you want to create an instance in the production environment only, do this:

val environment = parameter<String>("Environment")
val inProduction = "InProduction"
conditions(inProduction to (environment.ref() eq +"prod"))
instance(resourceProperties = ResourceProperties(condition = inProduction)){
    instanceType("m1.small")
}

This will produce the following:

Parameters:
  Environment:
    Type: "String"
Conditions:
  InProduction:
    Fn::Equals:
    - Ref: "Environment"
    - "prod"
Resources:
  Instance:
    Type: "AWS::EC2::Instance"
    Condition: "InProduction"
    Properties:
      InstanceType: "m1.small"

Conditional Intrinsic Functions

CloudFormation allows the use of intrinsic functions when creating a Condition

Here is a list of them and what they are called in KloudFormation:

And

conditions("InProdAndSizeIsHuge" to ((environment.ref() eq +"prod") and (size.ref() eq +"huge")))

Or

conditions("InDevOrTest" to ((environment.ref() eq +"dev") or (environment.ref() eq +"test")))

Equals

conditions("InProduction" to (environment.ref() eq +"prod"))

Not

conditions("NotInProd" to not(environment.ref() eq +"prod"))

If

The If function can be used in conjunction with a Condition. It will pick the first argument if the Condition is true and the second if it is false.

instance{
    //inProduction is a Condition name
    instanceType(If(inProduction, +"m1.large", +"t2.micro"))
}

AWS::NoValue

The If function can be useful in order to remove a value based on a condition. This can be done by using the awsNoValue() function

val dbSnapshotName = parameter<String>("DBSnapshotName")
val environment = parameter<String>("Environment")
val useDbSnapshot = "UseDBSnapshot"
conditions(useDbSnapshot to (environment.ref() eq +"prod"))
dBInstance(+"db.m1.small"){
    engine("MySQL")
    engineVersion("5.5")
    . . .
    dBSnapshotIdentifier(If(useDbSnapshot, dbSnapshotName.ref(), awsNoValue()))
}

This produces the following template

Parameters:
  DBSnapshotName:
    Type: "String"
  Environment:
    Type: "String"
Conditions:
  UseDBSnapshot:
    Fn::Equals:
    - Ref: "Environment"
    - "prod"
Resources:
  DBInstance:
    Type: "AWS::RDS::DBInstance"
    Properties:
      Engine: "MySQL"
      EngineVersion: "5.5"
      DBInstanceClass: "db.m1.small"
      DBSnapshotIdentifier:
        Fn::If:
        - "UseDBSnapshot"
        - Ref: "DBSnapshotName"
        - Ref: "AWS::NoValue"