Responsibilities: Maintain and enhance the backend services powering the SaaS platform ( Node.js/Express/NestJS with TypeScript ). Ensure uptime, scalability, and performance of APIs handling campaign generation, template storage, and credit-based billing. Optimize MongoDB queries , indexes, and caching strategies for high-performance APIs. Implement and manage Redis , job queues, and async workflows. Monitor and maintain AWS infrastructure: EC2, S3, CloudWatch, Lambda, SES. Implement security ?