System design interview question
Design a Distributed Session Store
A distributed session store keeps per-user session state for a stateless web tier so that any server can handle any request. The design must answer common authentication questions in under 5 ms, scale to hundreds of millions of active sessions, replicate across data centers for fail-over without exposing stale-session bugs, and support revocation (force-logout on password change, on a stolen device, on suspicious activity). The hardest part is the architecture trade-off itself: stateful Redis-backed sessions vs stateless JWTs, with deep implications for security, latency, and operational complexity.
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