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DynamoDB Stream Events

This is an AWS Lambda function that is triggered by DynamoDB Streams and creates EventBridge Events from the changes. You can then create rules on the EventBridge to react to these events.

The motivation behind this Lambda is to use DyanmoDB as a store of metadata or configuration information, and then use changes to it to trigger automation with EventBridge Rules.

Event Structure

All events have the same basic structure:

{
    "version": "0",
    "id": "RANDOM_GUID",
    "detail-type": "DynamoDB Streams Record (INSERT|REMOVE|MODIFY)",
    "source": "dynamodb-streams.aws.illinois.edu",
    "account": "ACCOUNT_ID",
    "time": "CHANGE_TIMESTAMP_ISO",
    "region": "REGION_NAME",
    "resources": [ "DYNAMODB_TABLE_ARN" ],
    "detail": {
        "ApproximateCreationDateTime": CHANGE_TIMESTAMP_FLOAT,
        "TableName": "DYNAMODB_TABLE_NAME",
        "Keys": {
            # DynamoDB Item Keys
        },
        "NewImage": {
            # New item values (for INSERT or MODIFY)
        },
        "OldImage": {
            # Old item values (for REMOVE or MODIFY)
        },
        "SequenceNumber": "SEQUENCE_ID",
        "SizeBytes": 999,
        "StreamViewType": "(NEW_IMAGE|OLD_IMAGE|NEW_AND_OLD_IMAGES)",
        "ChangedFields": [
            # Names of fields that changed between NewImage and OldImage
        ]
    }
}

The Keys, NewImage, and OldImage attributes are the unmarshalled DynamoDB types. For example: "Foo": 123 and not "Foo": { "N": "123" }.

Building

You can build the project by running make dist. This creates a zip file in the dist directory ready to be deployed to AWS.

Deployment

You can deploy with terraform, directly or using it as a module in another terraform.

Variables

environment

Type of environment this is serving:

  • prod, production
  • test
  • dev, development
  • devtest
  • poc

project

Project name within the service. This is used as part of resource names, so must be a simple alpha-numeric string.

dynamodb_table

The name of the DynamoDB Table to trigger from. This requires the table have streams enabled. If the table is encrypted with a CMK then is also generates an IAM policy that can decrypt table items.

event_detailtype_fmt

Python style format() string that controls how the event DetailType field is generated. If you do not specify a default value then it uses DynamoDB Streams Record {eventName}.

Default: ""

event_bus_name

Name of the EventBridge Bus to put events to. For most cases the default bus is fine, but you can create your own and have it use that.

Default: "default"

cloudwatch_logs_kms_key_id

The ARN of the KMS Key to use when encrypting log data.

Outputs

The module has a single output named lambda, which is a map of all values output by the terraform/aws/lambda module.