How To Build a Multi-Region DynamoDB Global Table with Conflict Resolution

In today’s globalized world, applications need to be highly available, scalable, and resilient to failures. Amazon DynamoDB, a fully managed NoSQL database service, offers a powerful feature called Global Tables that enables you to replicate your data across multiple AWS regions. This ensures low-latency access for users worldwide and provides disaster recovery capabilities. However, when data is replicated across regions, conflicts can arise due to concurrent writes. This article delves into building a multi-region DynamoDB Global Table and explores conflict resolution strategies, including last-write-wins and custom resolution logic.

Understanding DynamoDB Global Tables

DynamoDB Global Tables allow you to create a multi-region, multi-master database that automatically replicates data across specified AWS regions. Each region can accept writes, and DynamoDB handles the replication of data to other regions asynchronously. This setup ensures that your application can continue to operate even if one region becomes unavailable.

Key Features of DynamoDB Global Tables:

• Automatic Data Replication: Data is automatically replicated across regions with typical replication latency of under one second.
• Multi-Master Write Capability: Each region can accept writes, making the table highly available.
• Conflict Resolution: DynamoDB provides built-in conflict resolution mechanisms, such as last-write-wins, but also allows custom resolution logic.

Setting Up a Multi-Region DynamoDB Global Table

Prerequisites:

• An AWS account with permissions to create and manage DynamoDB tables.
• Familiarity with AWS CLI and AWS Management Console.
• Basic understanding of DynamoDB concepts like tables, items, and attributes.

Step 1: Create a DynamoDB Table in the Primary Region

Using AWS Management Console:

1. Log in to the AWS Management Console.
2. Navigate to the DynamoDB service.
3. Click Create Table.
4. Enter a table name (e.g., GlobalTable).
5. Set the primary key (e.g., PartitionKey as the partition key).
6. Configure any additional settings (e.g., provisioned capacity or on-demand mode).
7. Click Create.

Using AWS CLI:

aws dynamodb create-table \
    --table-name GlobalTable \
    --attribute-definitions AttributeName=PartitionKey,AttributeType=S \
    --key-schema AttributeName=PartitionKey,KeyType=HASH \
    --billing-mode PAY_PER_REQUEST \
    --region us-east-1

Step 2: Enable Streams on the Table

DynamoDB Streams are required for Global Tables as they capture changes to the table and replicate them across regions.

Using AWS Management Console:

1. Open the DynamoDB table you created.
2. Go to the Exports and Streams tab.
3. Enable DynamoDB Streams with the New and Old Images option.

Using AWS CLI:

aws dynamodb update-table \
    --table-name GlobalTable \
    --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES \
    --region us-east-1

Step 3: Add Replica Regions

Once the table is created and streams are enabled, you can add replica regions.

Using AWS Management Console:

1. Open the DynamoDB table.
2. Go to the Global Tables tab.
3. Click Add Region.
4. Select the region (e.g., eu-west-1).
5. Click Add.

Using AWS CLI:

aws dynamodb create-global-table \
    --global-table-name GlobalTable \
    --replication-group RegionName=us-east-1 RegionName=eu-west-1 \
    --region us-east-1

Step 4: Verify Replication

To verify that data is being replicated, insert an item into the table in one region and check if it appears in the other region.

Insert Data in us-east-1:

aws dynamodb put-item \
    --table-name GlobalTable \
    --item '{"PartitionKey": {"S": "Item1"}, "Attribute1": {"S": "Value1"}}' \
    --region us-east-1

Query Data in eu-west-1:

aws dynamodb get-item \
    --table-name GlobalTable \
    --key '{"PartitionKey": {"S": "Item1"}}' \
    --region eu-west-1

Conflict Resolution in DynamoDB Global Tables

When multiple regions accept writes concurrently, conflicts can occur. DynamoDB provides two primary conflict resolution strategies:

1. Last-Write-Wins (LWW): The most recent write based on a timestamp is accepted.
2. Custom Conflict Resolution: You can implement custom logic to resolve conflicts.

Last-Write-Wins (LWW)

DynamoDB uses a system-defined attribute called aws:rep:updatetime to determine the most recent write. The write with the highest timestamp wins.

Example:

• Region A writes an item at timestamp T1.
• Region B writes the same item at timestamp T2 (where T2 > T1).
• The item from Region B overwrites the item from Region A.

Custom Conflict Resolution

For more complex scenarios, you can implement custom conflict resolution logic using AWS Lambda. This involves:

1. Enabling DynamoDB Streams.
2. Creating a Lambda function to process stream records.
3. Implementing custom logic to resolve conflicts.

Step-by-Step Implementation:

Step 1: Create a Lambda Function

1. Open the AWS Lambda console.
2. Click Create Function.
3. Choose Author from scratch.
4. Enter a function name (e.g., ConflictResolver).
5. Select a runtime (e.g., Python 3.9).
6. Click Create Function.

Step 2: Add Permissions

Attach the following IAM policy to the Lambda function’s role:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "dynamodb:PutItem",
                "dynamodb:GetItem",
                "dynamodb:UpdateItem"
            ],
            "Resource": "arn:aws:dynamodb:*:*:table/GlobalTable"
        }
    ]
}

Step 3: Implement Custom Logic

Here’s an example of custom conflict resolution logic in Python:

import boto3
from datetime import datetime

dynamodb = boto3.client('dynamodb')

def lambda_handler(event, context):
    for record in event['Records']:
        if record['eventName'] == 'MODIFY':
            new_image = record['dynamodb']['NewImage']
            old_image = record['dynamodb']['OldImage']

            # Custom logic: Merge attributes from both images
            resolved_item = {**old_image, **new_image}

            # Update the item in the table
            dynamodb.put_item(
                TableName='GlobalTable',
                Item=resolved_item
            )

Step 4: Trigger Lambda from DynamoDB Streams

1. Open the DynamoDB table.
2. Go to the Exports and Streams tab.
3. Click Create Trigger.
4. Select the Lambda function you created.
5. Click Create.

Real-Life Use Cases and Case Studies

Use Case 1: Global E-Commerce Platform

An e-commerce platform uses DynamoDB Global Tables to ensure that product inventory and order data are consistent across regions. Custom conflict resolution logic ensures that inventory updates from different regions are merged correctly.

Use Case 2: Multi-Region Gaming Application

A gaming application uses Global Tables to store player profiles and game state. Last-write-wins is sufficient for most scenarios, but custom logic is implemented for critical updates like in-game purchases.

Best Practices for Multi-Region DynamoDB Global Tables

1. Monitor Replication Latency: Use CloudWatch to monitor replication latency and ensure it meets your application’s requirements.
2. Optimize Data Model: Design your data model to minimize conflicts (e.g., partition data by region where possible).
3. Test Conflict Resolution: Thoroughly test your conflict resolution logic to ensure it behaves as expected under all scenarios.
4. Use On-Demand Mode: For unpredictable workloads, use on-demand mode to avoid over-provisioning capacity.

Conclusion

Building a multi-region DynamoDB Global Table with conflict resolution is a powerful way to ensure high availability and low-latency access for global applications. By understanding and implementing both last-write-wins and custom conflict resolution logic, you can tailor the solution to your specific needs. Whether you’re running a global e-commerce platform or a multi-region gaming application, DynamoDB Global Tables provide the scalability and resilience required to meet modern application demands.

By following the steps and best practices outlined in this article, you can confidently deploy and manage a multi-region DynamoDB Global Table that meets your application’s requirements.

Sidra Saleem