Transforms do not support Conditions

[brandond]

If I put a Condition on a resource of type "AWS::Serverless::Function", this condition is neither honored by the transform, nor is it passed through to the resources created by the transform. This makes it impossible to conditionally create transformed resources.

Tracking Conditions support:

• Serverless::Function
  • Function resources (function, IAM role, etc) (v1.10.0)
  • Event resources (permissions, integrations, etc) (v1.10.0) (see Conditional event attachment #214 for tracking conditions support inside of events, which is not implemented in v1.10.0)
  • Implicit API: Issue RFC: Conditions and API Events #758
  • Alias (v1.10.0)
• Serverless::Api (v1.10.0)
• Serverless::LayerVersion (v1.10.0)
• Serverless::Application (v1.10.0)
• Serverless::SimpleTable (v1.10.0)

Note: this is only for conditions at the Resource (top) level. For conditions in Events (not yet implemented), see #214

[sanathkr]

Yup, feature request. We already have being implemented now. Will update once its ready.

[mikecbrant]

I would add that my experience has been not just having the transform silently ignore conditions, but rather to have the conditions cause errors (perhaps behavior depends upon where in resource definition the condition is?).

In my case, I was trying to conditionally set the "Path" property on an API event in AWS::Serverless:Function like the following:

      Events:
        GetByKey:
          Type: Api
          Properties:
            Path: !If [DynamoHasRangeKey, '/{hashKey}/{rangeKey}', '/{hashKey}']
            Method: get

The condition above fails when trying to create a change set with generic "internal transform failure" message.

The conditional shown below is in the same resource definition and seems to work just fine.

      Environment:
        Variables:
          !If
            - DynamoHasRangeKey
            -
              DYNAMO_TABLE: !Ref DynamoDbTable
              DYNAMO_HASH_KEY: !Ref DynamoHashKey
              DYNAMO_HASH_KEY_TYPE: !Ref DynamoHashKeyType
              DYNAMO_RANGE_KEY: !Ref DynamoRangeKey
              DYNAMO_RANGE_KEY_TYPE: !Ref DynamoRangeKeyType
            -
              DYNAMO_TABLE: !Ref DynamoDbTable
              DYNAMO_HASH_KEY: !Ref DynamoHashKey
              DYNAMO_HASH_KEY_TYPE: !Ref DynamoHashKeyType

As noted in the related issue I opened, it would at least be useful to get some documentation around current support for conditions (i.e. which specific properties are compatible with conditions),

[brandond]

@mikecbrant that's not a condition, that's a function that evaluates a conditional test (If). Conditions look like this:

AWSTemplateFormatVersion: "2010-09-09"
Conditions: 
  IsTargetRegion: !Equals [ !Ref "AWS::Region", "us-west-2" ]
Resources: 
  NewVolume: 
    Type: "AWS::EC2::Volume"
    Properties: 
      Size: 100
    Condition: IsTargetRegion

The resource gets skipped entirely if the condition evaluates to false.

[mikecbrant]

@brandond Yes, I suppose that would be proper nomenclature, however the intrinsic function in my example is tied to a condition that has defined in the Cloudformation template "Conditions" property (in this case DynamoHasRangeKey). That was probably not clear from my example. This functionality seems to break down in certain places in the template.

[glenveegee]

If conditional resource creation is eventually supported you might also have to support conditional events as in the following example where in some environments a bucket might not already exist and so it can be created and the event attached to the lambda. While in other environments the bucket may already exist and the trigger needs to be manually defined because cloudformation doesn't yet use existing resources.

For example

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Description: Lambda that responds to S3 events

Parameters:
    PreExistingBucket:
        Description: "Does an existing bucket exist (not managed by cloudformation)"
        Type: String
        Default: 'no'
        AllowedValues:
            - 'yes'
            - 'no'
        ConstraintDescription: must specify yes or no.

Conditions:
  NeedsSomeBucket: !Equals [ !Ref PreExistingBucket, 'no' ]

Resources:
    BucketEventConsumer:
        Type: AWS::Serverless::Function
        Properties:
            Handler: BucketEventConsumer.main.lambda_handler
            Runtime: python3.6
            CodeUri: bundle.zip
            Events:
                CreateMetaEvent:
                    Condition: NeedsSomeBucket
                    Type: S3
                    Properties:
                        Bucket: !Ref SomeBucket
                        Events: "s3:ObjectCreated:*"
                        Filter:
                            S3Key:
                                Rules:
                                    -
                                        Name: suffix
                                        Value: meta.json
    SomeBucket:
        Condition: NeedsSomeBucket
        Type: "AWS::S3::Bucket"
        Properties:
            BucketName: 'some-bucket-somewhere'
        DeletionPolicy: Retain

I'd like to draw your attention to the following crucial lines:

                CreateMetaEvent:
                    Condition: NeedsSomeBucket

[jfuss]

@glenveegee That is an interesting thought and idea! Would you mind create a new issue with this use case? It will help us prioritize this in the future and will ensure it does not get lost or forgotten about in this issue (since they are slightly different).

[glenveegee]

Sure. Moved to #214

[sanathkr]

Closing this in favor of #214

[brandond]

#224 is a completely separate request and should NOT replace this issue. This is just asking for conditionals to be honored (passed through) - for example, if I put a conditional on a AWS::Serverless::Function, I expect those conditions to be passed through to the resources that the function template expands to (Lambda, IAM role, etc).

[jfuss]

This was closed by mistake. Reopening.