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
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>