Question 1

What is the CAP theorem in system design?

Accepted Answer

The CAP theorem states that a distributed system can only guarantee two of three properties: Consistency, Availability, and Partition Tolerance. In practice, since network partitions are unavoidable, you must choose between CP (consistency + partition tolerance) or AP (availability + partition tolerance).

Question 2

What are the SOLID principles?

Accepted Answer

SOLID stands for: Single Responsibility (one class, one job), Open/Closed (open to extend, closed to modify), Liskov Substitution (subtypes must behave like parents), Interface Segregation (don't force unused implementations), and Dependency Inversion (depend on abstractions, not concretions).

Question 3

Sự khác biệt giữa var, let và const trong JavaScript là gì?

Accepted Answer

var có function scope và bị hoisting, let có block scope và không thể re-declare, const có block scope và không thể re-assign. Nên dùng const mặc định, let khi cần thay đổi giá trị, tránh dùng var.

Question 4

What is Apache Kafka and when should you use it?

Accepted Answer

Apache Kafka is a distributed event streaming platform designed for high-throughput, fault-tolerant real-time data pipelines. Use Kafka when you need to process millions of events per second with message replay capability, event sourcing, or decouple microservices.

Question 5

Redis là gì và tại sao nó nhanh?

Accepted Answer

Redis là in-memory data store sử dụng single-threaded event loop để xử lý commands, loại bỏ overhead của locking. Tất cả data lưu trong RAM nên latency cực thấp (sub-millisecond). Redis hỗ trợ nhiều data structures: String, Hash, List, Set, Sorted Set, Stream.