Amazon RDS initialization using CDK

Key	Value
Environment
Services	RDS, Lambda, SecretsManager, ECR
Integrations	AWS CDK, AWS SDK for JavaScript
Categories	Databases
Level	Intermediate
GitHub	Repository link

Introduction

The Amazon RDS initialization using CDK sample application demonstrates how LocalStack supports RDS instances initialization using CDK and CloudFormation Custom Resources. The sample application implements a Node.js Lambda function for compute layer, which is able to run custom SQL scripts. It also executes custom commands supported by the Node.js client for MySQL2. To test this application sample, we will demonstrate how you use LocalStack to deploy the infrastructure on your developer machine and your CI environment and use a Lambda function to run queries against the RDS database after successful deployment.

Architecture Diagram

The following diagram shows the architecture that this sample application builds and deploys:

• RDS as the central part of the sample application which is initialized and pre-filled with data.
• Lambda to initialize the database, and query data
• SecretsManager to store the credentials and configuration of the RDS database.

Prerequisites

• LocalStack Pro with the localstack CLI.
• AWS CLI with the awslocal wrapper.
• CDK with the cdklocal wrapper.
• Node.js

Instructions

You can build and deploy the sample application on LocalStack by running our Makefile commands: build, bootstrap, and deploy. Alternatively, here are instructions to deploy it manually step-by-step.

Run LocalStack

Start LocalStack Pro with the LOCALSTACK_API_KEY pre-configured:

export LOCALSTACK_API_KEY=<your-api-key>
localstack start

The sample application uses RDS with a MySQL Engine. Currently, by default LocalStack will use a MariaDB engine instead (check details in our RDS documentation). You can enable the use of real MySQL engine, which will start a MySQL instance in a separate docker container, by setting the env RDS_MYSQL_DOCKER=1. Run the following command to start LocalStack with MySQL engine:

export LOCALSTACK_API_KEY=<your-api-key>
RDS_MYSQL_DOCKER=1 localstack start

Installation

Install the project dependencies by running the following command:

npm install

Additionally, there is a Node.js Lambda located in demos/rds-query-fn-code that also requires external dependencies. Install these dependencies by navigating to the demos/rds-query-fn-code directory and running:

npm install && cd demos/rds-query-fn-code && npm install && cd ../../

Deploying the application

Once the dependencies are installed, run the following commands in the project's root directory:

cdklocal bootstrap
cdklocal deploy --require-approval never

This command deploys the application to LocalStack without requiring manual approval for each deployment step. Wait for the deployment to complete. Once finished, you will see some Outputs similar to the following:

RdsInitExample.RdsInitFnResponse = {"status":"OK","results":[{"fieldCount":0,"affectedRows":0,"insertId":0,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":0,"insertId":0,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":0,"insertId":0,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":0,"insertId":0,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":1,"insertId":1,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":1,"insertId":2,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":1,"insertId":3,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":1,"insertId":1,"info":"","serverStatus":10,"warningStatus":0},{"fieldCount":0,"affectedRows":1,"insertId":2,"info":"","serverStatus":2,"warningStatus":0}]}
RdsInitExample.functionName = my-lambda-rds-query-helper
RdsInitExample.secretName = /rdsinitexample/rds/creds/mysql-01

• RdsInitExample.RdsInitFnResponse shows the execution result of the SQL script (demos/rds-init-fn-code/script.sql).
• RdsInitExample.functionName is the name of the function that can be used to run test queries against RDS.
• RdsInitExample.secretName is the name of the secret that contains information about the database. This name is required as input for the Lambda to run queries.

Test the Sample

The sample application initializes the database with tables and dummy data. Additionally, we have included a Lambda function called my-lambda-rds-query-helper, which allows you to run queries against the RDS database.

The Lambda function expects two parameters: sqlQuery for the query itself, and secretName for the secret containing the database connection details.

For example, you query the authors of books like this for AWS CLI v1:

awslocal lambda invoke --function-name my-lambda-rds-query-helper --payload '{"sqlQuery": "select Author from books", "secretName":"/rdsinitexample/rds/creds/mysql-01"}' output

If you are using AWS CLI v2, please use the following:

awslocal lambda invoke --cli-binary-format raw-in-base64-out --function-name my-lambda-rds-query-helper --payload '{"sqlQuery": "select Author from books", "secretName":"/rdsinitexample/rds/creds/mysql-01"}' output

This command invokes the my-lambda-rds-query-helper function with the specified query and secret.

To view the result, use the following command:

cat output

The result will be displayed in the output, similar to the following:

{"status":"SUCCESS","results":[{"Author":"Jane Doe"},{"Author":"Jane Doe"},{"Author":"LocalStack"}]}

Use Cases

In the sample, we set up the database by creating tables and adding dummy data using the demos/rds-init-fn-code/scripts.sql script.

The setup process can be enhanced to cover various use cases, including:

• Initializing databases.
• Initializing and maintaining users and their permissions.
• Initializing and maintaining stored procedures, views, or other database resources.
• Executing custom logic as part of a resource initialization process. Improving segregation of duties and least privilege by providing a flexible hook in the Infrastructure-as-Code (IaC) to manage RDS instance initialization.
• Initializing database tables (see note below).
• Seeding database tables with initial datasets (see note below).

NOTE: Please note that application-specific initialization logic, such as defining the structure of database tables and seeding them with initial data, is typically managed on the application side. It is generally recommended to keep infrastructure initialization/management separate from application-specific initialization.

Technical Implementation Details

In order to achieve custom logic execution during the deployment flow of a CDK stack, we make use of CloudFormation Custom Resources. In the context of CDK, we use the AwsCustomResource construct to invoke a deployed Lambda containing the RDS initialization logic (execute SQL scripts).

Optionally you can read more about making custom AWS API calls using the AwsCustomResource construct.

Client implementation based on Node.js

To execute SQL scripts on the provisioned Amazon RDS instance we make use of the mysql NPM module, it allow us to easily execute custom SQL scripts or any other support client -> server command:

const mysql = require('mysql2')
const connection = mysql.createConnection({
  host,
  user,
  password,
  multipleStatements: true
})
connection.connect()

connection.query("SELECT 'Hello World!';", (err, res) => {
  // ...
})

Full Node.js implementation example for MySQL is available at ./demos/rds-init-fn-code/index.js

Docker container images for Lambda functions

To avoid unnecessary overhead dealing with software dependencies, we promote the usage of Docker container images to package the RDS initialization Lambda function code.

Docker container images are automatically managed by CDK and there is no need to interact with ECR repositories, simply use:

const fnCode = DockerImageCode.fromImageAsset(`${__dirname}/your-fn-code-directory`, {})

You can see a Lambda function code example inside the ./demos/rds-init-fn-code directory.

Lambda function for querying RDS

An additional Lambda function to show case querying of RDS database, uses code from assets. This requires to run npm install in the directory first, so that the node-modules are available.

// create a new Lambda to run queries against the database for testing purpose after init
const lambdaQuery = new lambda.Function(this, 'MyLambdaRDSQueryHelper', {
  code: new lambda.AssetCode(`${__dirname}/rds-query-fn-code`),
  handler: 'index.handler',
  runtime: lambda.Runtime.NODEJS_16_X,
  memorySize: 1024,
  timeout: cdk.Duration.seconds(300),
  functionName: "my-lambda-rds-query-helper"
})

The CdkResourceInitializer construct

The CDKResourceInitializer CDK construct generalizes the proposed solution, it encapsulates the integration requirements behind CloudFormation Custom Resources and CDK, to support the execution of AWS Lambda functions with custom initialization logic. The implementation can be found in lib/resource-initializer.ts.

Learn More

More details about the original sample can be found in the AWS blog post — Use AWS CDK to initialize Amazon RDS instances.

Contributing

We appreciate your interest in contributing to our project and are always looking for new ways to improve the developer experience. We welcome feedback, bug reports, and even feature ideas from the community. Please refer to the contributing file for more details on how to get started.