@ttoss/lambda-postgres-query

This package creates an AWS Lambda function that can query an RDS Postgres database inside a private subnet of a VPC.

The goal of this package is to provide a way to query a Postgres database from a Lambda function without exposing the database to the internet. If your project needs to query a Postgres database and access to the internet, you can follow two approaches:

1. Create a Lambda function inside a VPC and use a NAT Gateway to access the internet. This approach is expensive because you need to pay for the NAT Gateway.

2. Decompose your architecture into multiple Lambdas—some inside the VPC and some outside the VPC. The Lambda inside the VPC can query the database, and the Lambda outside the VPC can query the Lambda inside the VPC. On this approach, Lambdas outside the VPC invoke Lambdas inside the VPC using the AWS SDK to query the database. This approach is complex and requires more effort to maintain.

Check this StackOverflow question for more information: Why can't an AWS lambda function inside a public subnet in a VPC connect to the internet?

Installation

To install this package, you need to run the following command:

pnpm install @ttoss/lambda-postgres-query

Usage

CloudFormation

Create a src/cloudformation.ts file with the following content:

import { createLambdaPostgresQueryTemplate } from '@ttoss/lambda-postgres-query/cloudformation';

const template = createLambdaPostgresQueryTemplate();

export default template;

Create a src/handler.ts file with the following content:

export { handler } from '@ttoss/lambda-postgres-query';

Provide the following environment variables in the .env file:

DATABASE_NAME=
DATABASE_USERNAME=
DATABASE_PASSWORD=
DATABASE_HOST=
DATABASE_HOST_READ_ONLY=
DATABASE_PORT=
SECURITY_GROUP_IDS=
SUBNET_IDS=

Add the deploy script to the package.json file:

{
  "scripts": {
    "deploy": "carlin deploy"
  }
}

Deploy them using the following command:

pnpm deploy

Note: When deploying using carlin, you need to set lambdaFormat: 'cjs' because pg package doesn't support ESM format.

It'll create the necessary resources to query the Postgres database and display the name of the Lambda function created.

Querying the database

To query the database from Lambdas outside the VPC, do the following:

import { query } from '@ttoss/lambda-postgres-query';
import type { Handler } from 'aws-lambda';

export const handler: Handler = async (event) => {
  const text = 'SELECT * FROM table_name';
  const result = await query({ text });
  return result.rows;
};

API

createLambdaQueryTemplate

This function creates a CloudFormation template to deploy the Lambda function that queries the Postgres database.

query

This function queries the Postgres database using the environment variables provided. It uses the pg package to connect to the database.

Parameters

It accepts all the QueryConfig object from the pg package with the following additional properties:

• readOnly: A boolean that indicates if the query should be executed on the read-only database, in case you provided the DATABASE_HOST_READ_ONLY value. Default is true.
• lambdaPostgresQueryFunction: The name of the Lambda function that queries the database. Default is the value of the LAMBDA_POSTGRES_QUERY_FUNCTION environment variable.