System Design: Scalable Architecture for High-Traffic Govt Portals & CAP Theorem
Senior technical roles in NIC, C-DAC, and PSUs increasingly assess architectural design principles for national-scale digital public infrastructure (like Aadhaar, UPI, and Sarkari result portals).
In-Depth Interview Questions & Model Solutions
Q1How would you architect a Government Result Checking Portal that must handle 5 million concurrent requests upon result release?
Architecture strategy: (1) Static Asset Decoupling: Offload HTML/CSS/JS to a CDN (Cloudflare/Akamai/NIC CDN). (2) Multi-Tier Caching: Pre-generate student result payloads and cache them in an in-memory Redis cluster with Read Replicas (sub-millisecond lookups). (3) Rate Limiting & Queue: Implement token bucket rate limiting at NGINX API Gateway with Kafka queue to throttle surge queries. (4) Read-Only Database Replicas: Separate write OLTP database from sharded read replicas. (5) Static PDF Offloading: Host bulk result merit PDFs on distributed object storage with signed CDN links.
- CDN edge caching prevents 80% traffic from hitting backend servers.
- Redis cluster with key sharding handles millions of Read QPS.
- Graceful degradation with fallback static mirror servers.
Q2Explain the CAP Theorem and PACELC extension with practical examples.
CAP states that in a distributed data store experiencing a Network Partition (P), you can guarantee either Consistency (C - every read receives the most recent write) or Availability (A - every request receives a non-error response without guarantee of latest write). PACELC extends this: if there is a Partition (P), how does system trade Availability (A) vs Consistency (C); Else (E), how does it trade Latency (L) vs Consistency (C)? Example: MongoDB is PC/EC; Cassandra is PA/EL; DynamoDB is configurable PA/EL.
- RDBMS (Postgres/MySQL master-slave): CP or CA without partitions.
- Cassandra / DynamoDB: AP prioritizing high availability and eventual consistency.
- PACELC addresses normal operating conditions when no network fault exists.
Technical Panel Interview Strategy Tips
- Mention horizontal scaling over vertical scaling and explain stateless application server clusters.