CODEWITHSUNDEEP
amazon-web-servicesaws-cloudformation
Orest
Orest

Reputation: 6748

What will happen if we have false condition and Ref in CloudFormation?

I have this CloudFormation configuration:

Resources:
  DevoSnsTopic:
    Type: AWS::SNS::Topic
    Condition: UseDevoTopic
    ...
  SnsTopic:
    Type: AWS::SNS::Topic
    ...
  QueuePolicy:
    Properties:
       Condition:
          'ForAnyValue:ArnEquals':
             'aws:SourceArn':
               - Ref: SnsTopic
               - Ref: DevoSnsTopic

Will it break if UseDevoTopic equals false? Or it will simply skip reference for DevoSnsTopic?

UPD: Yes missing resource breaks the changeset!

Upvotes: 0

Views: 1782

Answers (2)

maafk
maafk

Reputation: 6876

If you're concerned with an invalid reference if the UseDevoTopic is false and DevoSnsTopic hasn't been created, you could use the Fn::If condition and provide the AWS::NoValue Pseudo Parmater if false

Resources:
  DevoSnsTopic:
    Type: AWS::SNS::Topic
    Condition: UseDevoTopic
    ...
  SnsTopic:
    Type: AWS::SNS::Topic
    ...
  QueuePolicy:
    Properties:
       Condition:
          'ForAnyValue:ArnEquals':
             'aws:SourceArn':
               - Ref: SnsTopic
               - !If [UseDevoTopic, !Ref DevoSnsTopic, AWS::NoValue]

Upvotes: 2

John Rotenstein
John Rotenstein

Reputation: 269540

A resource is only created if the Condition evaluates to true. It it is not true, then the resource will not be created.

This is a great way to deploy different resources (or resources with different attributes) between Dev/Test/Prod systems, or to do some if/then logic for specifying values.

Here's some snippets from a CloudFormation template that deploys differently based upon the region in which it is deployed:

"Conditions": {
    "InUsEast1": {
      "Fn::Equals": [
        {
          "Ref": "AWS::Region"
        },
        "us-east-1"
      ]
    },

Upvotes: 0

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