Deploying a full, three-tier book review web app on Azure

I designed and deployed one of my most hands-on cloud engineering projects: deploying a secure, scalable book review application using a full three-tier architecture on Microsoft Azure. But the real growth came from the challenge I hit along the way and how I solved it. The Problem I Encountered After deploying the backend (Node.js/Express) for the book review app in private subnets, the frontend couldn’t reach it. The internal load balancer was healthy, and the backend was running on port 3001, but every request from the frontend timed out. Everything looked correct: subnets, routes, health probes, VM status—yet the app simply wouldn’t connect. How I Solved It The issue turned out to be a Network Security Group (NSG) misconfiguration. The App Tier NSG wasn’t allowing inbound traffic from the Web Tier on port 3001, even though the internal load balancer was configured correctly. I fixed it by: •Updating the App Tier NSG •Allowing inbound traffic only from the Web Tier NSG •Opening port