DynamoDB Streams and Triggers

DynamoDB Streams captures a time-ordered sequence of item-level changes in a table. Combined with AWS Lambda, Streams enables powerful event-driven architectures, real-time processing, and change data capture (CDC) patterns.

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What are DynamoDB Streams?

When you enable Streams on a table, DynamoDB records every item-level change:

• INSERT — a new item is added
• MODIFY — an existing item is updated
• REMOVE — an item is deleted

Application → DynamoDB Table → DynamoDB Stream → Consumer
                                    │
                                    ├── Lambda Function
                                    ├── Kinesis Data Streams
                                    └── Custom Application

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Stream View Types

When enabling Streams, you choose what data to include in the stream record:

View Type	Description	Use Case
KEYS_ONLY	Only the primary key attributes	When you just need to know which item changed
NEW_IMAGE	The entire item after the change	Processing the current state
OLD_IMAGE	The entire item before the change	Auditing what was changed
NEW_AND_OLD_IMAGES	Both before and after	Comparing changes, computing deltas

Enabling Streams (AWS CLI)

aws dynamodb update-table \
  --table-name Orders \
  --stream-specification \
    StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES

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Stream Records

Each stream record contains:

Field	Description
eventID	Unique identifier for the stream record
eventName	INSERT, MODIFY, or REMOVE
dynamodb.Keys	Primary key of the changed item
dynamodb.NewImage	Item after the change (if applicable)
dynamodb.OldImage	Item before the change (if applicable)
dynamodb.SequenceNumber	Position in the stream
dynamodb.StreamViewType	The view type configured
eventSourceARN	ARN of the stream

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Lambda Triggers

The most common pattern is triggering an AWS Lambda function from a DynamoDB Stream:

How It Works

1. You create a Lambda function
2. You create an event source mapping that connects the Stream to Lambda
3. Lambda polls the Stream and invokes your function with batches of records
4. Your function processes the records

Creating an Event Source Mapping (AWS CLI)

aws lambda create-event-source-mapping \
  --function-name ProcessOrderChanges \
  --event-source-arn arn:aws:dynamodb:eu-west-1:123456789012:table/Orders/stream/2024-01-01T00:00:00.000 \
  --starting-position LATEST \
  --batch-size 100 \
  --maximum-batching-window-in-seconds 5

Lambda Function Example (Node.js)

exports.handler = async (event) => {
  for (const record of event.Records) {
    console.log('Event:', record.eventName);
    console.log('Keys:', JSON.stringify(record.dynamodb.Keys));

    if (record.eventName === 'INSERT') {
      const newItem = record.dynamodb.NewImage;
      // Process new order...
    } else if (record.eventName === 'MODIFY') {
      const oldItem = record.dynamodb.OldImage;
      const newItem = record.dynamodb.NewImage;
      // Process order update...
    } else if (record.eventName === 'REMOVE') {
      const oldItem = record.dynamodb.OldImage;
      // Process order deletion...
    }
  }
};

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Event Source Mapping Configuration