Feature Request: Add SQS Option to EventBridge

[chrisoverzero]

Describe your idea/feature/enhancement

Similar to how SAM allows SQS buffering for SNS events, I would like SAM to SQS-buffer EventBridge events.

Proposal

Mostly, I'll be modifying examples from the SNS–SQS proposal.

Given default settings for a queue (that is, a queue created by SAM):

Type: EventBridgeRule
Properties:
  EventBusName: ExternalEventBridge
  Pattern:
    detail:
      state:
      - terminated
  # new property that creates an SQS queue between the rule and Lambda function
  # When only the boolean is specified, SAM uses the following defaults:
  # AWS::SQS::Queue logicalId: <function logicalId><EventBridge event key>Queue
  # AWS::SQS::QueuePolicy logicalId: <function logicalId><EventBridge event key>QueuePolicy
  # BatchSize: default behavior - don't add to `AWS::Lambda::EventSourceMapping` resource so default value is used.
  # MaximumBatchingWindowInSeconds - don't add to `AWS::Lambda::EventSourceMapping` resource so default value is used.
  # Enabled: default behavior - don't add to `AWS::Lambda::EventSourceMapping` resource so default value is used.
  SqsSubscription: true

…or a modified example which specifies additional options for a queue:

Type: EventBridgeRule
Properties:
  EventBusName: ExternalEventBridge
  Pattern:
    detail:
      state:
      - terminated
  # new property that creates an SQS queue between the topic and Lambda function
  # Default values can be overridden by passing an object instead of a boolean. Supported keys:
  # QueuePolicyLogicalId: overrides default logicalId naming of the AWS::SQS::QueuePolicy resource.
  # QueueArn: allows the user to specify their own queue instead of having SAM create one on their behalf, allowing them to specify non-default properties on the queue.
  # BatchSize: if specified, add BatchSize property with given value to `AWS::Lambda::EventSourceMapping` resource.
  # MaximumBatchingWindowInSeconds: if specified, add MaximumBatchingWindowInSeconds property with given value to `AWS::Lambda::EventSourceMapping` resource.
  # Enabled: if specified, add Enabled property with given value to `AWS::Lambda::EventSourceMapping` resource.
  SqsSubscription:
    QueuePolicyLogicalId: CustomQueuePolicyLogicalId
    QueueArn: !GetAtt MyCustomQueue.Arn
    BatchSize: 25
    MaximumBatchingWindowInSeconds: 30
    Enabled: false

And, as in the other proposal, I expect that the AWS::SQS::QueuePolicy looks something like this:

ExampleQueuePolicy:
  Type: AWS::SQS::QueuePolicy
  Properties:
    Queues:
    - !Ref ExampleQueue
    PolicyDocument:
      Version: 2012-10-17
      Statement:
        Effect: Allow
        Principal:
          Service: !Sub events.${AWS::URLSuffix}
        Action: sqs:SendMessage
        Resource: !GetAtt ExampleQueue.Arn
        Condition:
          ArnEquals:
            aws:SourceArn: !GetAtt Example.Arn

I think that the QueueUrl property was added after the proposal was created, which will be necessary to create the queue policy. If this is grossly accepted, I will address those details in the implementation, natch.

Additional Details

I am able to take this work on soon, but not immediately. (Of course, if someone is motivated to get to it before I can, that’s great!)

This should rhyme with @53ningen's implementation of the SNS–SQS feature a lot, I think. Within my company, we use this pattern over and over and over, and I think that SAM can provide a good and related abstraction by synthesizing the rule and the queue policy here (as it does similarly for SNS).