This question evaluates skills in designing scalable real-time distributed systems, covering API design, message ordering and idempotency, fan-out strategies, storage tiers, indexing, sharding and replication, consistency vs.
Design a mobile-first, globally available real-time chat system that supports both 1:1 and group messaging at large scale (target: 100M daily active users). Assume multi-region deployment, clients are primarily mobile apps with intermittent connectivity, and the system must prioritize low latency and high availability.
Cover the following areas explicitly:
Make reasonable assumptions where needed and call them out explicitly.
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