Use NestJS's @nestjs/schedule module along with the Vonage Messages API. Create a scheduled task (cron job) that queries your database for upcoming appointments and sends SMS reminders via the Vonage API at the designated time before the appointment. This guide provides a complete walkthrough using PostgreSQL, Prisma, and other key technologies.

NestJS provides a structured, scalable backend framework. It facilitates API endpoint creation for scheduling, database integration with PostgreSQL via Prisma, and scheduled task management for sending SMS reminders through the Vonage Messages API. Its modular architecture and dependency injection simplify development and maintenance.

The Vonage Messages API allows you to programmatically send SMS messages. This is ideal for appointment reminders as it enables automation and ensures timely notifications to reduce no-shows and improve communication with users.

This guide uses PostgreSQL, a robust and open-source relational database, combined with Prisma, a modern database toolkit and ORM. Prisma simplifies database interactions and data modeling within the NestJS application.

These packages are crucial for request data validation. class-validator provides decorators for defining validation rules (e.g., required fields, data types, string length). class-transformer facilitates transforming request payloads into data transfer objects (DTOs), enforcing data integrity and security.

Obtain your API Key and API Secret from your Vonage API Dashboard. Store these securely in a .env file (never commit this to version control) and access them within your NestJS application using @nestjs/config for secure configuration management.

Use the Vonage CLI to create a new application with the Messages capability. The command vonage apps:create "My SMS Scheduler App" --capabilities=messages --messages_version=v1 --keyfile=private.key sets up an application and generates a private key file (ensure this key is stored securely).

A Vonage virtual number is required to send SMS messages via the Vonage API. After purchasing and linking a Vonage number to your application, add it to your .env file (VONAGE_SMS_FROM_NUMBER) as the sender ID for your reminders. Ensure the number is in E.164 format (+12015550123).

Never commit the private.key file to version control. Instead, manage it through a secure method such as environment variables, a dedicated secrets manager, or mounting it as a volume in containerized environments (e.g. Kubernetes secrets).

Prisma is a modern database toolkit that includes an ORM (Object-Relational Mapper). It simplifies database interactions, schema management, and data modeling in your Node.js and TypeScript applications, making it easier to work with PostgreSQL or other supported databases.

The @nestjs/schedule module allows you to define cron jobs (scheduled tasks). A cron job runs every minute (using CronExpression.EVERY_MINUTE) to check the database for appointments whose reminder time has passed but haven't had a reminder sent. If found, the app sends an SMS using the Vonage Messages API.

The @nestjs/config module provides a way to manage environment variables and application configuration securely. It helps access sensitive data like database credentials and API keys from a .env file without exposing them directly in the codebase. Create a .env.example file to track these environment variables.