Key Challenges in Designing a Billion-User Chat System Explained

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Designing a messaging service like WhatsApp presents complex distributed systems challenges beyond simple message exchange. The core design problem requires managing persistent connections, routing messages between stateful servers, and ensuring delivery for offline users. A typical technical interview for this prompt lasts about 45 minutes, focusing on high-level architecture and deep dives into critical components. Candidates are evaluated on their problem-solving approach and understanding of trade-offs, not on a single correct design. The process tests a candidate's ability to explain and justify technical decisions under time pressure.

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Guide to diagnosing systemd timers that fail to execute as expected

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