System design interview questionEasyBasic System Component
Design a Distributed Session Store
Design a distributed session store: many app servers must read/write user sessions fast and consistently enough after login.
Interview scope
Client → LB/Gateway → App → Cache (sessions). Optional DB for durable session backup. No Client → Cache.
Functional requirements
- Create a session after login.
- Validate/read session on subsequent requests.
- Expire or invalidate sessions (logout).
Scale and quality goals
- Very low latency reads on every authenticated request.
- Sessions must be shared across multiple app instances.
- Don’t store the only copy of sessions only in one app’s local memory.
Capacity assumption
Design for this scale
Assume ~50M session reads/day (~580 RPS average) and far fewer creates/updates.
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