Some time ago, I was building a chat application using AWS Websocket API gateway. Things were going smoothly. I created a WebSocket API Gateway, added $connect, $disconnect, and sendMessage/addGroup routes. From the frontend (React) side, everything was fire-and-forget. You send a message, and the onMessageHandler takes care of it 💪🏼 But then a new requirement of uploading files using S3 signed
Imagine you run a bustling coffee shop. In the beginning, you take orders, make the coffee, and serve pastries all by yourself. It works perfectly when you have a handful of customers. But as the crowd grows, you become the single point of failure. If you are stuck making a complex latte, the simple drip coffee line grinds to a halt. In software engineering, this "one-person shop" represents a mon
ID generation looks like a small backend decision. In many systems, we simply add an id column, make it the primary key, and move on. But once the table grows, this decision can affect database performance, indexing, pagination, debugging, and how easily the system scales across services. The common choices are: UUIDv4 UUIDv7 Snowflake ID Each one solves the uniqueness problem, but they behave dif
Java LLD: Designing a High-Concurrency Elevator System Designing an elevator system is a classic "Machine Coding" round favorite because it tests concurrency, state management, and algorithmic efficiency simultaneously. At companies like Apple or Amazon, interviewers aren't just looking for a working loop; they are looking for thread safety and optimal scheduling. Using a simple Queue<Integer>
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