AWS Cloudformation interprets conditionnal function as a resource property - amazon-web-services

Question

I'm having a strange behavior with cloudformation template. This my template, where I create a bucket and want to notification configuration depending on a condition :
AWSTemplateFormatVersion: '2010-09-09'
Description: "Setup Artifacts Bucket"
Parameters:
BucketName:
Description: Name of the pipeline setup arctifact bucket
Type: String
Default: "s3-pipeline-setup"
NotificationCondition:
Description: Conditionally add Notification configuration to the artifact bucket
Type: String
Default: false
Conditions:
AddNotificationConfiguration: !Equals [ !Ref NotificationCondition, true ]
Resources:
ArtifactBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Ref BucketName
Fn::If:
- AddNotificationConfiguration
-
NotificationConfiguration:
LambdaConfigurations:
-
Function: "arn:aws:lambda:eu-west-1:341292222222227:function:lambda-ops-trigger-pipeline-setup"
Event: "s3:ObjectCreated:*"
Filter:
S3Key:
Rules:
-
Name: prefix
Value: "appstackcodes/"
-
Name: suffix
Value: "txt"
- !Ref AWS::NoValue
When I try a deploy it fails with this error :
00:28:10
UTC+0200 CREATE_FAILED AWS::S3::Bucket ArtifactBucket Encountered
unsupported property Fn::If
I don't really understand the matter.. Can someone try and let me know the mistake there please?
Thanks

Answer 1

Unfortunately you can not do what you intended in cloudformation.
The Fn::If can basically just be used as a ternary expression. E.g.
key: Fn::If: [condition_name, value_if_true, value_if_false]
It can't be used as logic flow like you would in a programming language. There are ways around it. You actually already seemed to have discovered the AWS::NoValue, so it's just a matter of moving the NotificationConfiguration assignment to outside the if.
Resources:
ArtifactBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Ref BucketName
NotificationConfiguration:
Fn::If:
- AddNotificationConfiguration
- LambdaConfigurations:
-
Function: "arn:aws:lambda:eu-west-1:341294322147:function:lambda-itops-trigger-pipeline-setup"
Event: "s3:ObjectCreated:*"
Filter:
S3Key:
Rules:
-
Name: prefix
Value: "appstackcodes/"
-
Name: suffix
Value: "txt"
- !Ref AWS::NoValue
Effectively you are always assigning something to NotificationConfiguration, but sometimes it's the magic AWS::NoValue. This works in the majority of cases, although there are times when this just isn't sufficient and more creativity is required!