Currency Exchange Rate API using AWS CDK, Lambda, Dynamodb and API Gateway

The project implements a currency exchange rate backend component that uses Amazon API Gateway, AWS Lambda and Amazon DynamoDB to fetch the latest exchange rates from European Central Bank Website and provides basic APIs to:

• Get current exchange rates.
• How the exchange rate has changed compared to the previous day.

The project uses AWS CDK for deployment. It was set up using the aws-cdk-project-structure-python template provided by AWS.

Components

It has the following components:

Database

Dynamodb is used to store exchange rates info. The key is formed by concatenating currency and date. An additional index of date is defined to allow querying on date as well.

Update Exchange Rates Lambda Function

This Lambda function runs every 12 hours. It fetches the latest exchange rates from European Central Bank Website and stores them in dynamodb. It can be changed to run on a cron schedule as per requirement.

Get Exchange Rates Lambda Function

This lambda function is tied to API gateway and provides two functionalities.

• Get exchange rates and change in exchange rates for all currencies.
• Get exchange rates and change in exchange rates for a particular currency.

API Gateway

It creates an API gateway and ties to lambda function.

Monitoring

It creates a dashboard in Cloud Watch with two widgets:

• API Gateway metric count
• Dynamodb consumed read capacity unit metric count

Deployment

Unzip the provided archive file.

unzip python-cdk-apigw-lambda-dynamodb-main
cd python-cdk-apigw-lambda-dynamodb-main

Create Python virtual environment and install the dependencies

python3.8 -m venv .venv
source .venv/bin/activate

pip install pip-tools==6.4.0
pip install pip==21.3.1

./scripts/install-deps.sh

Deploy the component

The CurrencyExchangeRateBackend stack uses AWS account and region setup using CDK_DEFAULT_ACCOUNT and CDK_DEFAULT_REGION environment variables.

export CDK_DEFAULT_ACCOUNT=<YOUR_ACCOUNT>
export CDK_DEFAULT_REGION=<YOUR_REGION>
npx cdk bootstrap
npx cdk deploy CurrencyExchangeRateBackend

Example output for npx cdk deploy CurrencyExchangeRateBackend:

 ✅  CurrencyExchangeRateBackend

Outputs:
CurrencyExchangeRateBackend.APIEndpoint = https://afwaatt0j1.execute-api.us-west-2.amazonaws.com/
CurrencyExchangeRateBackend.UpdateCurrencyRateLambdaFunction = CurrencyExchangeRateBacke-LambdaUpdateCurrencyRate-84C3MQPW6KX6
Stack ARN:
arn:aws:cloudformation:us-west-2:007148109666:stack/CurrencyExchangeRateBackend/f95c7500-745d-11ed-a0c1-0612a202de15

Testing the API

The Update Exchange Rates lambda function executes every 12 hours. However, you may invoke it once, before testing. Below are examples that show the available resources and how to use them.

function_name=$(aws cloudformation describe-stacks \
  --stack-name CurrencyExchangeRateBackend \
  --query 'Stacks[*].Outputs[?OutputKey==`UpdateCurrencyRateLambdaFunction`].OutputValue' \
  --region $CDK_DEFAULT_REGION \
  --output text )

aws lambda invoke --function-name ${function_name} out --log-type Tail --region $CDK_DEFAULT_REGION
  
api_endpoint=$(aws cloudformation describe-stacks \
  --stack-name CurrencyExchangeRateBackend \
  --query 'Stacks[*].Outputs[?OutputKey==`APIEndpoint`].OutputValue' \
  --region $CDK_DEFAULT_REGION \
  --output text )

curl "${api_endpoint}/exchange_rates"

curl "${api_endpoint}/exchange_rates/USD"

Delete the stack

Do not forget to delete the stacks to avoid unexpected charges

npx cdk destroy CurrencyExchangeRateBackend