Using importValue inside If Condition in aws cloudformation templates - amazon-web-services

Question

I'm trying to find a way to use ImportValue inside If function but can't find a proper syntax. Any help is appreciated.
Below the code I'm trying:
SomeTaskdefinition:
Type: AWS::ECS::TaskDefinition
Properties:
Family: 'FamilyName'
ContainerDefinitions:
- Name: ContainerName
Image: 'imagename:net/v2/'
Environment:
- Name: ENV_VARIABLE_1
Value:
Fn::If:
Fn::Equals:
Fn::ImportValue:
!Sub "${ImportStackname}-ECSCluster"
''
'notpresent'
'present'

Answer 1

I come across here with similar problem.. my idea was to either be able specify DatabaseHost as parameter, if left empty - value should be taken from DatabaseStack export. Here is my sample code - it uses !ImportValue inside !If function. You will get the idea (instead of constructing only Value - construct whole Name Value list object)
Conditions:
DatabaseHostPresent: !Not [ !Equals [ !Ref DatabaseHost, ""]]
Resources:
...
ContainerDefinitions:
- Name: !Sub ${ApplicationName}-web-${EnvironmentName}
Environment:
- !If
- DatabaseHostPresent
- Name: DB_HOST
Value: !Ref DatabaseHost
- Name: DB_HOST
Value: !ImportValue
Fn::Sub: ${DatabaseStack}-EndpointAddress

Answer 2

I don't believe this is possible. You cannot use ImportValue inside an Equals function.

Answer 3

Another way to work around this is to use a nested template:
Add a Parameter to the Child template
In the Parent template, use the Import to populate the Parameter
In the Child template, you can do everything you'd want including using it in the Conditions section
Untested example:
# in Parent
Resources:
ChildStack:
Type: 'AWS::CloudFormation::Stack'
Properties:
Parameters:
Stackname: {'Fn::ImportValue': !Sub "${ImportStackname}-ECSCluster"}
TemplateURL: './child.yaml'
# in Child
Parameters:
Stackname:
Type: String
Default: ''
Conditions:
HasStack: !Not [!Equals [!Ref Stackname, '']]
Resources:
SomeTaskdefinition:
Type: AWS::ECS::TaskDefinition
Properties:
Family: 'FamilyName'
ContainerDefinitions:
- Name: ContainerName
Image: 'imagename:net/v2/
Environment:
- Name: ENV_VARIABLE_1
Value: !If [HasStack, 'present', 'notpresent']

Answer 4

Using a combination of intrinsic function I've obtained the result:
parameter1: !If
- condition1
- !ImportValue
Fn::Sub: "${name}-dev-parameter"
- AWS::NoValue
Make sure to use the sequence of intrinsic function as I've listed. It seems to be the only way.