You can send bulk SMS messages by creating a NestJS application that integrates with AWS SNS. The application uses the AWS SDK to interact with the SNS service, sending messages to specified phone numbers. You'll need an AWS account and configure credentials within your NestJS project.

AWS SNS (Simple Notification Service) is used as the messaging platform to deliver SMS messages to recipients. It handles the complexities of sending messages reliably at scale. The NestJS application acts as an interface to interact with SNS.

NestJS provides a structured and scalable architecture based on TypeScript and Node.js. This makes it well-suited for building robust applications capable of handling the demands of bulk SMS messaging.

Create an IAM user in your AWS account with permissions to use SNS, generate access keys, and store them securely in a `.env` file in your project's root directory. Never commit this file to version control.

A Data Transfer Object (DTO) defines the structure of incoming requests. In this case, the `SendBulkSmsDto` ensures that the API receives valid phone numbers and message content, using validation decorators from `class-validator`.

The provided code uses `Promise.allSettled` to handle individual SMS failures without stopping the entire batch. Logging is implemented using NestJS's built-in `Logger`, and the code includes a detailed explanation of how to implement retry mechanisms for transient errors.

The `SnsService` encapsulates the logic for interacting with AWS SNS. It initializes the SNS client, sets default message attributes, and provides methods to send single and bulk SMS messages. It also handles errors and provides a summary of sent messages.

Create a controller with a POST route that accepts a `SendBulkSmsDto` object. This DTO should contain an array of phone numbers and the message content. The controller then uses the `SnsService` to send the messages.

Use HTTP status code 202 (Accepted), as the actual SMS delivery is asynchronous. This acknowledges that the request has been received and is being processed, even if individual messages fail later.

Use the `class-validator` library. The `SendBulkSmsDto` demonstrates how to validate phone numbers using decorators like `@IsArray`, `@ArrayNotEmpty`, `@IsString`, and a regex `@Matches` to enforce E.164 format.

You'll need an AWS account with SNS permissions, AWS access keys, Node.js and npm/yarn, a basic understanding of NestJS and TypeScript, and optionally, a database for logging.

Use 'Transactional' for critical messages requiring high reliability, like one-time passwords. 'Promotional' is suitable for marketing messages where lower cost is preferred. This is configurable in the '.env' file and used by the `SnsService`.

Yes, you can set `SNS_DEFAULT_SENDER_ID` in your `.env` file. However, support for custom sender IDs varies by country and may require registration with AWS. See AWS documentation for details.

The article suggests using a database to log sent messages, including details like phone number, message content, status, SNS message ID, and errors. It outlines a TypeORM setup with SQLite as an example.