Yi-Ju C.

🚀 Mindset shifts that get you from #SDE2 → Senior Engineer at #Amazon Most engineers get stuck because they treat growth as: “Do more. Ship more. Work harder.” But at Senior level, performance isn’t measured in lines of code. It’s measured in impact. Here’s the mindset shift I’ve seen in every engineer who made the leap 👇 🔄 From: “I finished my tasks” To: “I moved the business forward” #SDE1 / #SDE2 success = execution. Senior success = identifying the right problems and driving them end-to-end. 🚫 From: “Who can unblock me?” To: “Who can I unblock?” Your value shifts from what you deliver → to how effectively you multiply the team’s delivery. 🧱 From: “I know how it works” To: “I know why it matters” Deep technical knowledge isn’t enough. You must connect engineering choices to: ⚡ Customer experience 📈 Revenue impact 🛡️ System and business risk That’s senior thinking. 💡 Truth: The jump to Senior isn’t a harder version of your current job. It’s a different job. If you want to grow faster, ask yourself each week: ✔ What business problem did I help solve? ✔ Who is moving faster because of me? ✔ Did my work create leverage beyond myself? 👉 Engineers — what mindset shift helped you level up in your career? #Amazon #Engineering #TechCareers #CareerAdvice #Leadership #SDE2 #SeniorEngineer

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You are in a system design interview at Meta (which owns WhatsApp) for the IC4 role The interviewer leans in and asks: "Why can I log into Discord or Slack on a new laptop and instantly see my old chats, but WhatsApp needs a backup or a long 'restoring history' step? I asked you to design a chat application. How would these two approaches change your system?" Here is how you should break it down 👇 Both WhatsApp and Discord look like simple chat apps. Under the hood, they are built on two very different philosophies. Btw, we’ve recently launched our system design mock interview tool at Layrs. If you’re preparing for a switch or SD interviews, it’s free to use: http://layrs.me/interviews 1. WhatsApp – Phone is the source of truth Idea: Your device is the real database. The server is mostly a courier. What happens when you send a message: – You type the message. – It is encrypted on your phone with keys stored only on devices in that chat. – WhatsApp server receives the encrypted blob, stores it briefly, and forwards it to the receiver. – Once all devices in that chat acknowledge, the server is allowed to drop the message content. – Your long-term history lives in a local database on phone (SQLite style), plus whatever you back up to iCloud or Google Drive. What this means: – New phone, no backup = almost no history. – Multi device is hard, because every device needs keys and a copy of messages. – Server cost is lower, because they are not keeping infinite message history for every user. – Privacy is strong. Even WhatsApp cannot easily scan your chat content, because they do not keep decrypted data. In your design answer, you can mention: + Local storage on device + End to end encryption + Store and forward model + Optional cloud backup handled as a separate flow 2. Discord or Slack – Server is the source of truth Idea: Servers hold a permanent log of messages. Your device is just a window. What happens when you send a message: – You hit send. The message goes to a backend service. – Backend writes it into a big distributed database or log store (for example Cassandra or ScyllaDB). – Indexes and partitions are based on channel, user, time, workspace, so reads scale horizontally. – Any device that logs in simply fetches messages from the server and renders them. What this means: – New laptop, new browser, office desktop, phone, all show the same history instantly. – Multi device is easy, because all devices just read from the same central store. – Server cost is higher. You are paying to store years of chat history and to replicate it. – Privacy tradeoff. Company can run search, analytics, and moderation on server side data. In your design answer, you can mention: + Distributed database for messages + Append only style message log + Search indexes, pagination, and caching + Stronger focus on availability and horizontal scalability Check my 1st comment as well:

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