INTERVIEW QUESTIONS

System Design Interview Questions

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SYSTEM DESIGN

What is the difference between horizontal and vertical scaling?

Vertical scaling (scaling up) involves adding more compute power, RAM, or storage to an existing server, which is simple but has a hard hardware ceiling and creates a single point of failure. Horizontal scaling (scaling out) involves adding more machine nodes to the pool behind a load balancer, providing virtually unlimited scalability, fault tolerance, and elasticity, but introducing distributed system complexities like network latency and data consistency.

CompanyGoogle◦ Scalability

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SYSTEM DESIGN

What is the role and importance of a Load Balancer in distributed systems?

A load balancer distributes incoming network traffic across multiple backend servers to prevent any single server from becoming a bottleneck and to ensure high availability. It performs continuous health checks, offloads SSL/TLS termination, and uses algorithms like Round Robin, Least Connections, and IP Hash to route requests efficiently.

CompanyAmazon◦ Architecture

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SYSTEM DESIGN

What is the difference between a Reverse Proxy and a Forward Proxy?

A forward proxy sits in front of clients and mediates outgoing requests to the internet, commonly used for anonymity, enterprise policy enforcement, and client-side caching. A reverse proxy sits in front of backend web servers, intercepting incoming public traffic to provide load balancing, caching, SSL termination, rate limiting, and DDoS mitigation.

CompanyCloudflare◦ Networking

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SYSTEM DESIGN

What is the CAP Theorem and how does it influence database selection?

The CAP theorem states that a distributed data store can guarantee at most two out of three guarantees: Consistency (every read gets the most recent write), Availability (every non-failing node returns a response), and Partition Tolerance (the system functions despite arbitrary network message drops). Because network partitions are inevitable in distributed systems, architects must choose between CP (e.g., HBase, MongoDB in strict mode) and AP (e.g., Cassandra, DynamoDB).

CompanyMeta◦ Distributed Systems

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SYSTEM DESIGN

What is a Content Delivery Network (CDN) and how does it reduce latency?

A CDN is a geographically distributed network of proxy servers and data centers (Edge Locations) that caches static assets like images, videos, HTML, and CSS near end users. By serving content from the nearest Point of Presence (PoP), CDNs minimize round-trip network hops, absorb sudden traffic spikes, and offload significant bandwidth from origin servers.

CompanyNetflix◦ Performance

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