(aws-events-targets): (Add support for Predefined variables for Input transformers)

[luisMolina95]

Describe the feature

Currently there is no available feature to make use of Predefined variables.

AWSEventField would work the same way as EventField but for the AWS Predefined variables ( aws.events.rule-arn, aws.events.event.json, aws.events.rule-name, aws.events.event.ingestion-time, aws.events.event ).

Use Case

Without Predefined variables available in CDK, we need to keep deploying changes to the input transformer, and keep manually adding attributes with RuleTargetInput.

When we could instead just use aws.events.event.json to add the original event and then add the additional metadata but rigth now there is no option to use Predefined variables at all.

Proposed Solution

For example this code:

import { RuleTargetInput, AWSEventField } from "aws-cdk-lib/aws-events";

const ruleTargetInput = RuleTargetInput.fromObject({
      // Currently this does not work,  it is configured as a Constant rather than as an Input Transformer.
      // ruleName: "<aws.events.rule-name>",
      // originalEvent: "<aws.events.event.json>",
      // This new feature would make it possible:
      ruleName: AWSEventField.ruleName,
      originalEvent: AWSEventField.eventJSON ,
    });

Would generate the following stack template (an empty object input map and an input template with only Predefined variables):

{
  "Arn": {
    "Fn::GetAtt": ["function", "Arn"]
  },
  "Id": "Target0",
  "InputTransformer": {
    "InputPathsMap": { },
    "InputTemplate": "{\"ruleName\":<aws.events.rule-name>,\"originalEvent\":<aws.events.event.json>}"
  }
}

Other Information

https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-transform-target-input.html#eb-transform-input-predefined

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

2.104.0

Environment details (OS name and version, etc.)

Windows 10