🏗️ System Design & Architecture Interview Questions & Answers (2025)
Basic Level Questions
What is system design?▶
System design is the process of defining the architecture, components, modules, and data for a system to satisfy specified requirements.
What are the key components of system architecture?▶
Key components typically include clients, servers, databases, APIs, caching layers, load balancers, and network infrastructure.
What is a monolithic architecture?▶
Monolithic architecture is a software design where all components are tightly integrated and run as a single service.
What is microservices architecture?▶
An architectural style that structures an application as a collection of loosely coupled, independently deployable services.
What is load balancing?▶
Load balancing distributes incoming network or application traffic across multiple servers to ensure reliability and performance.
What is caching in system design?▶
Caching stores frequently accessed data temporarily to reduce latency and improve system performance.
What is a database?▶
A database is a structured collection of data, managed by a database management system for storage, retrieval, and manipulation.
What is the difference between horizontal and vertical scaling?▶
Horizontal scaling adds more machines to handle load; vertical scaling adds more resources (CPU, RAM) to existing machines.
What is an API?▶
An API (Application Programming Interface) is a set of rules and protocols that allows different software components to communicate.
What is latency?▶
Latency is the time delay experienced in a system, typically how long it takes a request to be processed end-to-end.
Intermediate Level Questions
What is a message queue and why is it used?▶
Message queues facilitate asynchronous communication between services or components by buffering messages, improving scalability and fault tolerance.
Explain the CAP theorem.▶
In distributed systems, CAP theorem states that a system can simultaneously provide only two of Consistency, Availability, and Partition tolerance.
What is database sharding?▶
Sharding partitions a database into smaller, faster, and more manageable parts called shards that can be distributed across servers.
What is eventual consistency?▶
A consistency model where updates to a distributed system will propagate eventually, and all replicas will converge to the same state.
Difference between SQL and NoSQL databases?▶
SQL databases are relational and use structured query language; NoSQL databases are non-relational and designed for flexible schema and horizontal scaling.
What is a CDN?▶
Content Delivery Network (CDN) distributes content geographically closer to users to reduce latency and improve load times.
Explain data replication.▶
Data replication involves copying data across multiple machines to ensure fault tolerance and high availability.
What are the techniques for ensuring system reliability?▶
Techniques include redundancy, failover mechanisms, health checks, graceful degradation, and circuit breakers.
What is containerization?▶
Packaging an application and its dependencies into a container for consistent deployment across different environments.
What is the role of an API Gateway?▶
API Gateway manages, routes, and secures API traffic between clients and backend services, often handling authentication, rate limiting, and monitoring.
Explain different types of load balancers.▶
Types include Layer 4 (Transport level) and Layer 7 (Application level) load balancers, handling traffic differently based on OSI model layers.
What is horizontal scaling?▶
Adding more instances or machines to a system to distribute load and improve capacity.
How do you secure REST APIs?▶
Use authentication, authorization, HTTPS, input validation, rate limiting, and API keys or OAuth tokens.
What is circuit breaker pattern?▶
A pattern to prevent cascading failures by stopping requests to failing services and allowing recovery time.
Explain rate limiting.▶
Controlling the number of requests a client can make to a system within a given time to prevent abuse and overload.
What are RESTful APIs?▶
APIs following REST architectural principles, stateless communication, and standard HTTP methods for CRUD operations.
What is eventual consistency and where is it used?▶
Consistency model where system guarantees data will be consistent eventually; often used in distributed databases.
Explain database indexing.▶
A data structure improving query performance by allowing faster data retrieval.
What is CDN and CDN caching?▶
CDN caches static content at edge locations near users to reduce latency and load on origin servers.
What are WebSockets?▶
A communication protocol providing full-duplex communication channels over a single TCP connection for real-time applications.
What is the difference between synchronous and asynchronous communication in system design?▶
Synchronous communication waits for a response before continuing; asynchronous communication proceeds without waiting.
Advanced Level Questions
What is event-driven architecture?▶
An architecture where components communicate via events, allowing decoupled systems and improved scalability.
Explain CQRS (Command Query Responsibility Segregation).▶
A pattern separating read and write operations into different models to optimize performance, scalability, and security.
What are microservices communication patterns?▶
Includes synchronous HTTP/REST, asynchronous messaging, event streaming, and gRPC based on requirements and latency.
What is the trade-off between consistency, availability, and partition tolerance?▶
In the CAP theorem, distributed systems can guarantee only two of these three simultaneously, forcing trade-offs based on use case.
How do you ensure data security in distributed systems?▶
Through encryption at rest and transit, access controls, secure protocols, auditing, and regular vulnerability assessments.
What is backpressure in system design?▶
A mechanism to handle overwhelming incoming requests by controlling or slowing input to prevent system overload.
Describe the concept of consistency models in distributed systems.▶
Models like strong, eventual, causal, and read-your-writes consistency define how data visibility and updates propagate.
Explain the design considerations for high availability.▶
Use redundancy, failover, replication, load balancing, health checks, and disaster recovery plans.
What is the role of a service mesh?▶
A service mesh manages service-to-service communication, providing features like load balancing, security, and observability transparently.
How do you design a scalable notification system?▶
Use message queues, fan-out mechanisms, push notifications, and ensure persistence with retries and monitoring.
Explain database partitioning strategies.▶
Horizontal partitioning (sharding), vertical partitioning, and functional partitioning to improve performance and manageability.
How do you implement fault tolerance?▶
Through replication, failover, retries, idempotent operations, and monitoring to detect and recover from failures quickly.
What is load shedding?▶
Dropping excess traffic or requests when the system is overloaded to maintain overall system stability.
What is eventual consistency and how do you handle conflicts?▶
Eventual consistency means data updates eventually propagate; conflicts are resolved via timestamps, version vectors, or application logic.
What is data lake and how does it differ from data warehouse?▶
Data lakes store raw, unstructured data at scale; data warehouses store structured, processed data optimized for analysis.
What is throttling?▶
Throttling controls the usage of resources by limiting client request rates to prevent abuse or overload.
Explain how to design a URL shortening service.▶
Use hashing or unique ID generation, database for mapping, caching, and a redirection mechanism with scalability considerations.
What are bloom filters and their use-cases?▶
A space-efficient probabilistic data structure used to test membership with false positives, used in caching and databases.
What is backpressure and how do you handle it?▶
Backpressure manages data flow to prevent resource exhaustion by signaling producers to slow down or buffer data.
How do you design a recommendation system?▶
Use collaborative filtering, content-based filtering, or hybrid approaches with data storage, ranking, and personalization.