Tutorial: Using AWS Lambda with Amazon DynamoDB Streams

In this tutorial, you create a Lambda function to consume events from an Amazon DynamoDB stream.

Prerequisites

This tutorial assumes that you have some knowledge of basic Lambda operations and the Lambda console. If you haven't already, follow the instructions in Getting Started with AWS Lambda to create your first Lambda function.

To follow the procedures in this guide, you will need a command line terminal or shell to run commands. Commands are shown in listings preceded by a prompt symbol ($) and the name of the current directory, when appropriate:

~/lambda-project$ this is a command
this is output

For long commands, an escape character (\) is used to split a command over multiple lines.

On Linux and macOS, use your preferred shell and package manager. On Windows 10, you can install the Windows Subsystem for Linux to get a Windows-integrated version of Ubuntu and Bash.

Create the Execution Role

Create the execution role that gives your function permission to access AWS resources.

To create an execution role

1. Open the roles page in the IAM console.

2. Choose Create role.

3. Create a role with the following properties.

   • Trusted entity – Lambda.

   • Permissions – AWSLambdaDynamoDBExecutionRole.

   • Role name – lambda-dynamodb-role.

The AWSLambdaDynamoDBExecutionRole has the permissions that the function needs to read items from DynamoDB and write logs to CloudWatch Logs.

Create the Function

The following example code receives a DynamoDB event input and processes the messages that it contains. For illustration, the code writes some of the incoming event data to CloudWatch Logs.

Note

For sample code in other languages, see Sample Function Code.

Example index.js

console.log('Loading function');

exports.handler = function(event, context, callback) {
    console.log(JSON.stringify(event, null, 2));
    event.Records.forEach(function(record) {
        console.log(record.eventID);
        console.log(record.eventName);
        console.log('DynamoDB Record: %j', record.dynamodb);
    });
    callback(null, "message");
};

To create the function

1. Copy the sample code into a file named index.js.

2. Create a deployment package.

   $ zip function.zip index.js

3. Create a Lambda function with the create-function command.

   $ aws lambda create-function --function-name ProcessDynamoDBRecords \
   --zip-file fileb://function.zip --handler index.handler --runtime nodejs12.x \
   --role arn:aws:iam::123456789012:role/lambda-dynamodb-role

Test the Lambda Function

In this step, you invoke your Lambda function manually using the invoke AWS Lambda CLI command and the following sample DynamoDB event.

Example input.txt

{
   "Records":[
      {
         "eventID":"1",
         "eventName":"INSERT",
         "eventVersion":"1.0",
         "eventSource":"aws:dynamodb",
         "awsRegion":"us-east-1",
         "dynamodb":{
            "Keys":{
               "Id":{
                  "N":"101"
               }
            },
            "NewImage":{
               "Message":{
                  "S":"New item!"
               },
               "Id":{
                  "N":"101"
               }
            },
            "SequenceNumber":"111",
            "SizeBytes":26,
            "StreamViewType":"NEW_AND_OLD_IMAGES"
         },
         "eventSourceARN":"stream-ARN"
      },
      {
         "eventID":"2",
         "eventName":"MODIFY",
         "eventVersion":"1.0",
         "eventSource":"aws:dynamodb",
         "awsRegion":"us-east-1",
         "dynamodb":{
            "Keys":{
               "Id":{
                  "N":"101"
               }
            },
            "NewImage":{
               "Message":{
                  "S":"This item has changed"
               },
               "Id":{
                  "N":"101"
               }
            },
            "OldImage":{
               "Message":{
                  "S":"New item!"
               },
               "Id":{
                  "N":"101"
               }
            },
            "SequenceNumber":"222",
            "SizeBytes":59,
            "StreamViewType":"NEW_AND_OLD_IMAGES"
         },
         "eventSourceARN":"stream-ARN"
      },
      {
         "eventID":"3",
         "eventName":"REMOVE",
         "eventVersion":"1.0",
         "eventSource":"aws:dynamodb",
         "awsRegion":"us-east-1",
         "dynamodb":{
            "Keys":{
               "Id":{
                  "N":"101"
               }
            },
            "OldImage":{
               "Message":{
                  "S":"This item has changed"
               },
               "Id":{
                  "N":"101"
               }
            },
            "SequenceNumber":"333",
            "SizeBytes":38,
            "StreamViewType":"NEW_AND_OLD_IMAGES"
         },
         "eventSourceARN":"stream-ARN"
      }
   ]
}

Execute the following invoke command.

$ aws lambda invoke --function-name ProcessDynamoDBRecords --payload file://input.txt outputfile.txt

The function returns the string message in the response body.

Verify the output in the outputfile.txt file.

Create a DynamoDB Table with a Stream Enabled

Create an Amazon DynamoDB table with a stream enabled.

To create a DynamoDB table

1. Open the DynamoDB console.

2. Choose Create table.

3. Create a table with the following settings.

   • Table name – lambda-dynamodb-stream

   • Primary key – id (string)

4. Choose Create.

To enable streams

1. Open the DynamoDB console.

2. Choose Tables.

3. Choose the lambda-dynamodb-stream table.

4. Under Overview, choose Manage stream.

5. Choose Enable.

Write down the stream ARN. You need this in the next step when you associate the stream with your Lambda function. For more information on enabling streams, see Capturing Table Activity with DynamoDB Streams.

Add an Event Source in AWS Lambda

Create an event source mapping in AWS Lambda. This event source mapping associates the DynamoDB stream with your Lambda function. After you create this event source mapping, AWS Lambda starts polling the stream.

Run the following AWS CLI create-event-source-mapping command. After the command executes, note down the UUID. You'll need this UUID to refer to the event source mapping in any commands, for example, when deleting the event source mapping.

$ aws lambda create-event-source-mapping --function-name ProcessDynamoDBRecords \
 --batch-size 100 --starting-position LATEST --event-source DynamoDB-stream-arn

This creates a mapping between the specified DynamoDB stream and the Lambda function. You can associate a DynamoDB stream with multiple Lambda functions, and associate the same Lambda function with multiple streams. However, the Lambda functions will share the read throughput for the stream they share.

You can get the list of event source mappings by running the following command.

$ aws lambda list-event-source-mappings

The list returns all of the event source mappings you created, and for each mapping it shows the LastProcessingResult, among other things. This field is used to provide an informative message if there are any problems. Values such as No records processed (indicates that AWS Lambda has not started polling or that there are no records in the stream) and OK (indicates AWS Lambda successfully read records from the stream and invoked your Lambda function) indicate that there are no issues. If there are issues, you receive an error message.

If you have a lot of event source mappings, use the function name parameter to narrow down the results.

$ aws lambda list-event-source-mappings --function-name ProcessDynamoDBRecords

Test the Setup

Test the end-to-end experience. As you perform table updates, DynamoDB writes event records to the stream. As AWS Lambda polls the stream, it detects new records in the stream and executes your Lambda function on your behalf by passing events to the function.

1. In the DynamoDB console, add, update, and delete items to the table. DynamoDB writes records of these actions to the stream.

2. AWS Lambda polls the stream and when it detects updates to the stream, it invokes your Lambda function by passing in the event data it finds in the stream.

3. Your function executes and creates logs in Amazon CloudWatch. You can verify the logs reported in the Amazon CloudWatch console.