DynamoDB - Cross Account Replication using SAM and AWS sdk v2

This project contains java source code and supporting files for a serverless application that you can deploy with the SAM CLI / Intellij IDEA with AWS Toolkit. It includes the following files and folders.

• LambdaFunction/src/main/* - Code for the application's Lambda function.
• LambdaFunction/src/test/* - Unit tests for the application code.
• template.yaml - A template that defines the application's AWS resources.
• pom.xml - A pom file with dependencies for JAVA 8 runtime.

The application uses several AWS resources, including Lambda functions, DynamoDB, IAM Role. These resources are defined in the template.yaml file in this project. You can update the template to add AWS resources through the same deployment process that updates your application code. Note: IAM Role for Source and Target Account are defined outside of template.yaml as a good practice

Source IAM Role: DDB-CAR-Source-Role

• AWSLambdaBasicExecutionRole
• AWSLambdaDynamoDBExecutionRole
• DDB-CAR-TrustPolicy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "sts:GetSessionToken",
                "sts:DecodeAuthorizationMessage",
                "sts:GetAccessKeyInfo",
                "sts:GetCallerIdentity",
                "sts:GetServiceBearerToken"
            ],
            "Resource": "*"
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": "sts:*",
            "Resource": "arn:aws:iam::{Target-Account-Number}:role/DDB-CAR-Role"
        }
    ]
}

Source IAM Role: Trust Policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::{Target-Account-Number}:root",
                "Service": "lambda.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {}
        }
    ]
}

Target IAM Role: DDB-CAR-Role

• DDB-CAR-Policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "dynamodb:BatchGetItem",
                "dynamodb:BatchWriteItem",
                "dynamodb:PutItem",
                "dynamodb:DescribeTable",
                "dynamodb:DeleteItem",
                "dynamodb:GetItem",
                "dynamodb:Scan",
                "dynamodb:Query",
                "dynamodb:UpdateItem"
            ],
            "Resource": "arn:aws:dynamodb:ap-south-1:{Target-Account-Number}:table/Target-DDB"
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": "dynamodb:ListTables",
            "Resource": "*"
        }
    ]
}

Target IAM Role: Trust Policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": [
                    "arn:aws:iam::{Source-Account-Number}:root",
                    "arn:aws:iam::{Source-Account-Number}:role/DDB-CAR-Source-Role"
                ]
            },
            "Action": "sts:AssumeRole",
            "Condition": {}
        }
    ]
}

If you prefer to use an integrated development environment (IDE) to build and test your application, you can use the AWS Toolkit.
The AWS Toolkit is an open source plug-in for popular IDEs that uses the SAM CLI to build and deploy serverless applications on AWS. The AWS Toolkit also adds a simplified step-through debugging experience for Lambda function code. See the following links to get started.

• CLion
• GoLand
• IntelliJ
• WebStorm
• Rider
• PhpStorm
• PyCharm
• RubyMine
• DataGrip
• VS Code
• Visual Studio

Deploy the sample application

The Serverless Application Model Command Line Interface (SAM CLI) is an extension of the AWS CLI that adds functionality for building and testing Lambda applications. It uses Docker to run your functions in an Amazon Linux environment that matches Lambda. It can also emulate your application's build environment and API.

To use the SAM CLI, you need the following tools.

• SAM CLI - Install the SAM CLI
• Java8 - Install the Java SE Development Kit 8
• Maven - Install Maven
• Docker - Install Docker community edition

To build and deploy your application for the first time, run the following in your shell:

sam build
sam deploy --guided

The first command will build the source of your application. The second command will package and deploy your application to AWS, with a series of prompts:

• Stack Name: The name of the stack to deploy to CloudFormation. This should be unique to your account and region, and a good starting point would be something matching your project name.
• AWS Region: The AWS region you want to deploy your app to.
• Confirm changes before deploy: If set to yes, any change sets will be shown to you before execution for manual review. If set to no, the AWS SAM CLI will automatically deploy application changes.
• Allow SAM CLI IAM role creation: Many AWS SAM templates, including this example, create AWS IAM roles required for the AWS Lambda function(s) included to access AWS services. By default, these are scoped down to minimum required permissions. To deploy an AWS CloudFormation stack which creates or modifies IAM roles, the CAPABILITY_IAM value for capabilities must be provided. If permission isn't provided through this prompt, to deploy this example you must explicitly pass --capabilities CAPABILITY_IAM to the sam deploy command.
• Save arguments to samconfig.toml: If set to yes, your choices will be saved to a configuration file inside the project, so that in the future you can just re-run sam deploy without parameters to deploy changes to your application.

You can find your API Gateway Endpoint URL in the output values displayed after deployment.

Use the SAM CLI to build and test locally

Build your application with the sam build command.

DDB-CAR$ sam build

The SAM CLI installs dependencies defined in LambdaFunction/pom.xml, creates a deployment package, and saves it in the .aws-sam/build folder.

Test a single function by invoking it directly with a unit test. An event is a JSON document that represents the input that the function receives from the event source is configured in test/resources folder.

Add a resource to your application

The application template uses AWS Serverless Application Model (AWS SAM) to define application resources. AWS SAM is an extension of AWS CloudFormation with a simpler syntax for configuring common serverless application resources such as functions, triggers, and APIs. For resources not included in the SAM specification, you can use standard AWS CloudFormation resource types.

Fetch, tail, and filter Lambda function logs

To simplify troubleshooting, SAM CLI has a command called sam logs. sam logs lets you fetch logs generated by your deployed Lambda function from the command line. In addition to printing the logs on the terminal, this command has several nifty features to help you quickly find the bug.

NOTE: This command works for all AWS Lambda functions; not just the ones you deploy using SAM.

DDB-CAR$ sam logs -n LambdaFunction --stack-name DDB-CAR --tail

You can find more information and examples about filtering Lambda function logs in the SAM CLI Documentation.

Unit tests

Tests are defined in the LambdaFunction/src/test folder in this project.

DDB-CAR$ cd LambdaFunction
LambdaFunction$ mvn test

Cleanup

To delete the sample application that you created, use the AWS CLI. Assuming you used your project name for the stack name, you can run the following:

sam delete --stack-name DDB-CAR

Resources

See the AWS SAM developer guide for an introduction to SAM specification, the SAM CLI, and serverless application concepts.