dynamodb: FIXED capacity mode should be supported

[liusongdu]

Describe the bug

Creating a TableV2 with provisioned billing fails if I specify fixed capacity for WCU.

Error: You cannot configure 'writeCapacity' with FIXED capacity mode

Using fixed capacity for DynamoDB table provision mode should be supported by CDK, as it is supported by CloudFormation.

CDK don't support configuring 'writeCapacity' with FIXED capacity mode, however, this is supported by CloudFormation.
https://github.com/aws/aws-cdk/tree/main/packages/aws-cdk-lib/aws-dynamodb#billing
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-dynamodb-table.html

Expected Behavior

My table's capacity is well known so I don't need the autoscaling. The FIXED write capacity mode should be supported by DynamoDB CDK.

Current Behavior

Currently, the write capacity field of the DynamoDB CDK only support autoscaling capacity.

Reproduction Steps

new TableV2(this, my-table, {
billing: Billing.provisioned({
readCapacity: Capacity.fixed(3),
writeCapacity: Capacity.fixed(1),
}),
}

Possible Solution

Support fixed capacity for WCU.

Additional Information/Context

No response

CDK CLI Version

2.100.0

Framework Version

No response

Node.js Version

v18.17.1

OS

Linux

Language

Python

Language Version

3.9.16

Other information

No response

[liusongdu]

Below is a CloudFormation template to create DynamoDB table with WCU fixed:

cdk_dynamodb_wcu.txt

[khushail]

Hi @liusongdu , Here its described how the TableV2 construct can be configured with provisioned billing-

When using provisioned billing, you must also specify readCapacity and writeCapacity. You can choose to configure readCapacity with fixed capacity or autoscaled capacity, but writeCapacity can only be configured with autoscaled capacity. The following example shows how to configure TableV2 with provisioned billing:

const table = new dynamodb.TableV2(this, 'Table', {
  partitionKey: { name: 'pk', type: dynamodb.AttributeType.STRING },
  billing: dynamodb.Billing.provisioned({
    readCapacity: dynamodb.Capacity.fixed(10),
    writeCapacity: dynamodb.Capacity.autoscaled({ maxCapacity: 15 }),
  }),
});

what you have shared in the cloudformation template, that is in accordance with what is implemented by CDK. The provisionedThroughputDescription object accepts the value a stated.

So the feature requested by you is not do-able as its not supported by Cloudformation.

Past Similar request -#27378

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[liusongdu]

Setting fixed WCU, I do think it is supported by CloudFormation. The evidence is the attached CloudFormation template example. So my understand is that only CDK not support this, but CloudFormation does. @khushail

Hi @liusongdu , Here its described how the TableV2 construct can be configured with provisioned billing-

When using provisioned billing, you must also specify readCapacity and writeCapacity. You can choose to configure readCapacity with fixed capacity or autoscaled capacity, but writeCapacity can only be configured with autoscaled capacity. The following example shows how to configure TableV2 with provisioned billing:

const table = new dynamodb.TableV2(this, 'Table', {
  partitionKey: { name: 'pk', type: dynamodb.AttributeType.STRING },
  billing: dynamodb.Billing.provisioned({
    readCapacity: dynamodb.Capacity.fixed(10),
    writeCapacity: dynamodb.Capacity.autoscaled({ maxCapacity: 15 }),
  }),
});

what you have shared in the cloudformation template, that is in accordance with what is implemented by CDK. The provisionedThroughputDescription object accepts the value a stated.

So the feature requested by you is not do-able as its not supported by Cloudformation.

Past Similar request -#27378

[christophercurrie]

For everyone else coming here confused: TableV2 is built on top of the AWS::DynamoDB::GlobalTable resource, not the AWS::DynamoDB::Table resource. The GlobalTable resource does not support fixed write capacity, hence this construct cannot support it.