System Design Answers

Basic System Design Answers

#	Question	Answer	Examples
1	What is System Design?	The process of defining the architecture, components, and interfaces of a software system	Designing a URL shortener, a social media feed, a chat application
2	What is Scalability?	The ability of a system to handle increasing load (users, data, requests)	Scaling horizontally (adding more servers) or vertically (upgrading one server)
3	What is Horizontal Scaling?	Adding more machines/servers to a system to distribute the load	Adding more web servers behind a load balancer
4	What is Vertical Scaling?	Increasing the resources (CPU, RAM) of a single server	Upgrading a server to a more powerful machine
5	What is a Load Balancer?	Distributes incoming network traffic across multiple servers	Nginx, HAProxy, AWS ELB
6	What is a Database?	A system for storing, managing, and retrieving data	Relational (MySQL, PostgreSQL), NoSQL (MongoDB, Cassandra)
7	What is a Relational Database (SQL)?	Stores data in tables with rows and columns; uses SQL for queries	Ensures data consistency, good for structured data
8	What is a NoSQL Database?	Non-relational database; uses various data models (document, key-value, graph)	Often more scalable and flexible for unstructured or semi-structured data
9	What is Caching?	Storing frequently accessed data in a faster, temporary storage location	Redis, Memcached, CDN (Content Delivery Network)
10	What is a CDN (Content Delivery Network)?	A distributed network of servers that cache content (images, CSS, JS) closer to users	Reduces latency and improves website performance
11	What is an API (Application Programming Interface)?	A set of rules and protocols that allows different software components to communicate	REST APIs, GraphQL APIs
12	What is a REST API?	An architectural style for designing networked applications; uses HTTP methods (GET, POST, PUT, DELETE)	Resource-based URLs, stateless communication
13	What is Redundancy?	Having multiple copies of data or systems running simultaneously	Prevents single points of failure, improves fault tolerance
14	What is Availability?	The degree to which a system is accessible and operational when needed	High availability (e.g., 99.9% uptime)
15	What is Latency?	The time it takes for a request to be processed and a response to be returned	Minimizing latency improves user experience

Intermediate System Design Answers

#	Question	Answer	Examples
1	What is Microservices Architecture?	Breaking down a monolithic application into smaller, independent services that communicate over a network	User Service, Order Service, Product Service communicating via APIs
2	What is Database Sharding?	Splitting a large database into smaller, more manageable pieces (shards) based on a key	Distributing user data across multiple servers based on user_id
3	What is Database Replication?	Copying data from one database (master) to another (slave) for redundancy or load balancing	Master-slave replication for read scaling.
4	What is a Message Queue?	A system for asynchronous communication between application components (e.g., RabbitMQ, Kafka)	Decoupling services, handling spikes in traffic, processing background tasks.
5	What is Asynchronous Processing?	Performing tasks in the background without blocking the main user request thread	Sending emails after user registration, processing images, generating reports.
6	What is Idempotency?	An operation that can be performed multiple times with the same effect as performing it once	Sending the same payment request multiple times should only result in one charge.
7	What is Fault Tolerance?	The ability of a system to continue operating even when some components fail	Using redundant servers, failover mechanisms, circuit breakers.
8	What is a Circuit Breaker Pattern?	A pattern to prevent cascading failures by stopping requests to a failing service	Prevents repeated requests from overwhelming downstream services.
9	What is Rate Limiting?	Restricting the number of requests a client can make to an API within a specific time frame	Preventing denial-of-service attacks, ensuring fair usage.
10	What is an API Gateway?	A single entry point for all client requests, handling routing, authentication, rate limiting, etc.	Centralizes API management for microservices.
11	How do you design a URL Shortener?	Typically uses hashing and a database to map short URLs to long URLs	Generating unique short codes, storing mappings, redirecting requests.
12	How do you design a Social Media Feed?	Involves handling user profiles, posts, followers, and generating personalized feeds efficiently	Fan-out on write (pushing posts to followers) vs. Fan-out on read (fetching posts from followed users).
13	What is the difference between stateless and statefull APIs?	REST APIs are typically stateless (server doesn't store client state); Statefull APIs maintain client state	Stateless APIs are easier to scale horizontally.
14	What is the concept of Distributed Transactions?	Transactions that are executed across multiple services (e.g., using 2PC or avoided in modern distributed systems)	Ensuring consistency across multiple databases or microservices.
15	What is the purpose of Distributed Locking?	Ensuring exclusive access to a shared resource in a distributed system (e.g., using Redis, ZooKeeper)	Prevents race conditions when multiple services try to modify the same data.

Advanced System Design Answers

#	Question	Answer	Examples
1	What is the CAP Theorem?	A distributed system can only guarantee two out of three: Consistency, Availability, Partition Tolerance	Understanding trade-offs when designing distributed systems.
2	What is Eventual Consistency?	Data will eventually become consistent across all nodes, but there might be temporary inconsistencies	Common in systems prioritizing high availability over immediate consistency (e.g., NoSQL databases, CDNs).
3	What is a Distributed Consensus Algorithm (e.g., Paxos, Raft)?	Algorithms that allow nodes in a distributed system to agree on a single value or state	Used for leader election, distributed configuration management, distributed transactions.
4	What is Two-Phase Commit (2PC)?	A protocol for coordinating distributed transactions, ensuring all participants either commit or abort	Simple but blocking protocol for ensuring atomicity across multiple resources.
5	What is Saga Pattern?	A sequence of local transactions where each transaction triggers a compensating transaction in case of failure	Used to manage distributed transactions in microservices when 2PC is unsuitable.
6	What is CQRS (Command Query Responsibility Segregation)?	Separating the model for reading data (queries) from the model for writing data (commands)	Allows using separate models for read and write operations (e.g., using relational DB for writes, document for reads).
7	What is Event Sourcing?	Storing the state of an application as a sequence of immutable events, rather than just the current state	Allows auditing, time travel, and rebuilding state (e.g., using Kafka or event store).
8	What is the purpose of Distributed Tracing?	Tracking a request as it flows through multiple services in a distributed system	Tools like Jaeger, Zipkin, OpenTelemetry.
9	What is the purpose of Centralized Logging?	Collecting logs from all distributed services into a central location for analysis	ELK Stack (Elasticsearch, Logstash, Kibana), Splunk.
10	What is the purpose of Monitoring and Alerting?	Tracking the health, performance, and availability of a system; notifying operators of issues	Prometheus, Grafana, Datadog, PagerDuty.
11	How do you design a Real-time Chat System?	Involves handling WebSocket connections, message queues, user presence, message history	Using Socket.IO, Kafka/RabbitMQ, Redis for presence, Cassandra/MongoDB for message history.
12	How do you design a Rate Limiter?	Implementing mechanisms to control the number of requests a client can make within a time period	Token Bucket, Leaky Bucket, Fixed Window, Sliding Window Counter.
13	How do you design a Search Engine?	Involves indexing data, ranking results, and handling large volumes of queries	Using Elasticsearch, Solr, or custom solutions (e.g., based on Lucene).
14	What is the concept of A/B Testing?	Randomly dividing users into groups to test different versions of a feature or UI	Used to measure the impact of changes on user behavior.
15	What is Feature Flags (Toggles)?	A technique used to turn features on or off remotely without deploying new code	Enables gradual rollout, canary deployments, rollback during incidents.