Parameterize list of replica regions in DynamoDB SAM Template

Question

I am trying to parameterize value of regions in Replica/Region property of DynamoDB SAM Template using 2 methods - one using sam toml file, another with hardcoded values.
1. Using samconfig.toml as: 
* parameter-overrides section to have "ddbregionlist=\"us-east-1,us-east-2\""
* template.yml to have

```
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: SAM Template for deployment of DynamoDB resources

Parameters:
  ddbregionlist:
    Type: CommaDelimitedList
    Default: "us-east-1, us-east-2"

Resources:
  #-------------------** DynamoDB Table **--------------------

DDBTable:
    Type: AWS::DynamoDB::GlobalTable
    Properties:
      TableName: ddbtable
      AttributeDefinitions:
        - AttributeName: "id"
          AttributeType: "S"
      KeySchema:
        - AttributeName: "id"
          KeyType: "HASH"
      BillingMode: "PAY_PER_REQUEST"
      StreamSpecification: 
        StreamViewType: NEW_AND_OLD_IMAGES
      Replicas:
        - Region: !Select [ 0, !Ref ddbregionlist ]
        - Region: !Select [ 1, !Ref ddbregionlist ]
```

2. With direct hardcoded values for Replica Regions - everything same template as above with difference as below -

```
Replicas:
        - Region: !Select [ 0, [ "us-east-1", "us-east-2" ] ]
        - Region: !Select [ 1, [ "us-east-1", "us-east-2" ] ]
```

None of the above methods is working and here the portion of log which I am seeing.

Unable to resolve property Region: OrderedDict([('Fn::Select', ['0', ['us-east-1', 'us-east-2']])]). Leaving as is.

Resource handler returned message: "Resource of type 'AWS::DynamoDB::GlobalTable' with identifier 'ddbtable' did not stabilize." (RequestToken: <....>, HandlerErrorCode: NotStabilized)

Possibly, samconfig values are not getting passed, however, hardcoded values in #2 should have worked as per this link - [https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-select.html].

I suppose, I am using correct syntax. Can someone please help me resolve this ?
Thanks in advance.

Answer

Hi,

Thanks for the formatting of the question.

Your problem may come from the fact that you specify the indices as strings "0", "1" while they should be integers 0,1 when in YAML as per documentation: see section "Comma-delimited list parameter type" of https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/parameters-section-structure.html

Best,

Didier

Parameterize list of replica regions in DynamoDB SAM Template

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