AWS SAM DynamoDB Application for Managing Packages

Requirements

AWS CLI already configured with at least PowerUser permission
Java SE Development Kit 8 installed
Docker installed
Maven
SAM CLI
Python 3

Setup process

Installing dependencies

We use maven to install our dependencies and package our application into a JAR file:

mvn clean package

Local Installation Recipe

Invoking function locally through local API Gateway

Create docker network bridge. docker network create dynamodb-network
Start DynamoDB Local in a Docker container. docker run -d -v "$PWD":/dynamodb_local_db -p 8000:8000 --network dynamodb-network --name dynamodb cnadiminti/dynamodb-local
Create the DynamoDB table. aws dynamodb create-table --table-name products_table --attribute-definitions AttributeName=productId,AttributeType=S --key-schema AttributeName=productId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 --endpoint-url http://localhost:8000
List created tables on DynamoDB . aws dynamodb list-tables --endpoint-url http://localhost:8000
Start the SAM local API.

On a Mac: sam local start-api -d 5858 --docker-network dynamodb-network -n src/test/resources/test_environment_mac.json
On Windows: sam local start-api -d 5858 --docker-network dynamodb-network -n src/test/resources/test_environment_windows.json
On Linux: sam local start-api -d 5858 --docker-network dynamodb-network -n src/test/resources/test_environment_linux.json

Basic API calls

curl --location --request POST 'http://127.0.0.1:3000/products' \
--header 'Content-Type: application/json' \
--data-raw '{
  "productType" : "box",
  "deliveryDate" : "2020-10-08 13:00 - 15:00"
}

curl --location --request GET 'http://127.0.0.1:3000/products/3fce08a3-cc35-46a5-a440-e2d1b43d2979'

curl --location --request GET 'http://127.0.0.1:3000/packages'

If the previous command ran successfully you should now be able to create and get product inside of the package to hit the following local endpoint to invoke the functions rooted at http://localhost:3000/products

SAM CLI is used to emulate both Lambda and API Gateway locally and uses our template.yaml to understand how to bootstrap this environment (runtime, where the source code is, etc.) - The following excerpt is what the CLI will read in order to initialize an API and its routes:

...
Events:
    GetPackages:
        Type: Api
        Properties:
            Path: /packages
            Method: get

Database Approach

In terms of the CAP theorem, DynamoDB is an Available & Partition-tolerant (AP) database with eventual write consistency. On the read front, it supports both eventually consistent and strongly consistent reads. However, strongly consistent reads in DynamoDB are not highly available in the presence of network delays and partitions. Since such failures are common in multi-region/global apps running on public clouds such as AWS, DynamoDB tries to reduce such failures by limiting strongly consistent reads only to a single region. This in turn makes DynamoDB unfit for most multi-region apps and an unreliable solution for even single-region apps.

Packaging and deployment

AWS Lambda Java runtime accepts either a zip file or a standalone JAR file - We use the latter in this example. SAM will use CodeUri property to know where to look up for both application and dependencies:

...
    GetPackagesFunction:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: target/package-service-1.0.0.jar
            Handler: com.postnl.handler.GetPackagesHandler::handleRequest

Firstly, we need a S3 bucket where we can upload our Lambda functions packaged as ZIP before we deploy anything - If you don't have a S3 bucket to store code artifacts then this is a good time to create one:

export BUCKET_NAME=my_cool_new_bucket
aws s3 mb s3://$BUCKET_NAME

Next, run the following command to package our Lambda function to S3:

sam package \
    --template-file template.yaml \
    --output-template-file packaged.yaml \
    --s3-bucket $BUCKET_NAME

Next, the following command will create a Cloudformation Stack and deploy your SAM resources.

sam deploy \
    --template-file packaged.yaml \
    --stack-name sam-packageHandler \
    --capabilities CAPABILITY_IAM

After deployment is complete you can run the following command to retrieve the API Gateway Endpoint URL:

aws cloudformation describe-stacks \
    --stack-name sam-packageHandler \
    --query 'Stacks[].Outputs'

Testing

Running unit tests

We use JUnit for testing our code. Unit tests in this sample package mock out the DynamoDBTableMapper class for Product objects. Unit tests do not require connectivity to a DynamoDB endpoint. You can run unit tests with the following command:

mvn clean test

Running integration tests

Integration tests in this sample package do not mock out the DynamoDBTableMapper and use a real AmazonDynamoDB client instance. Integration tests require connectivity to a DynamoDB endpoint, and as such the POM starts DynamoDB Local from the Dockerhub repository for integration tests.

mvn clean verify

The number that follows the test script name is the number of products to create in the test. For these tests to work, you must follow the steps for local development.

Appendix

AWS CLI commands

AWS CLI commands to package, deploy and describe outputs defined within the cloudformation stack:

sam package \
    --template-file template.yaml \
    --output-template-file packaged.yaml \
    --s3-bucket REPLACE_THIS_WITH_YOUR_S3_BUCKET_NAME

sam deploy \
    --template-file packaged.yaml \
    --stack-name sam-packageHandler \
    --capabilities CAPABILITY_IAM \
    --parameter-overrides MyParameterSample=MySampleValue

aws cloudformation describe-stacks \
    --stack-name sam-packageHandler --query 'Stacks[].Outputs'

ofkntr/package-service