Question 1

What defines a distributed system, and what are its main challenges?

Accepted Answer

A distributed system is a collection of independent computers that appear to users as a single coherent system. These machines communicate and coordinate their actions by passing messages over a network.

Key characteristics include multiple autonomous components working together. No single machine has complete information about the entire system state. Components can fail independently without bringing down the whole system. The system continues operating despite partial failures.

Distributed systems are everywhere in modern computing. Cloud services, microservices architectures, content

Question 2

What are the main data replication strategies in distributed systems?

Accepted Answer

Data replication maintains copies of data on multiple nodes to improve availability, durability, and read performance. Different strategies offer different trade-offs between consistency, latency, and fault tolerance.

Single-leader replication, also called master-slave or primary-secondary, designates one node as the leader that handles all writes. Followers replicate from the leader and can serve reads. This is simple to understand and implement. Writes are consistent because they go through one node. However, the leader is a single point of failure for writes, and replication lag can caus

Question 3

Explain the SOLID principles and why they matter for maintainable software.

Accepted Answer

SOLID is an acronym for five design principles that help create maintainable, flexible, and understandable object-oriented software.

The Single Responsibility Principle states that a class should have only one reason to change. Each class should focus on one concern. A UserService that handles authentication, sends emails, and generates reports violates this principle. Instead, separate these into AuthenticationService, EmailService, and ReportService.

The Open-Closed Principle states that software entities should be open for extension but closed for modification. You should add new func

Question 4

What is dependency injection, and what benefits does it provide?

Accepted Answer

Dependency injection is a design pattern where objects receive their dependencies from external sources rather than creating them internally.

Constructor injection is the most common approach. The dependency is required at object creation, making dependencies explicit. This is preferred for required dependencies.

Setter injection provides dependencies through setter methods after construction. Useful for optional dependencies but can leave objects partially initialized.

Method injection passes dependencies as method parameters when the dependency varies between calls.

Benefits incl

Question 5

What is the difference between authentication and authorization, and how do they work together?

Accepted Answer

Authentication and authorization are two distinct security concepts that work together to protect systems.

Authentication, often abbreviated AuthN, verifies identity. It answers the question: who are you? The user proves their identity through credentials like passwords, biometrics, or security tokens. After successful authentication, the system knows who is making requests.

Authorization, often abbreviated AuthZ, determines permissions. It answers the question: what are you allowed to do? Once identity is established, authorization decides which resources and actions the authenticated u

Question 6

How should passwords be stored securely, and why should you never store them in plain text?

Accepted Answer

Passwords must never be stored in plain text because database breaches happen. If attackers obtain your database and passwords are plain text, every account is immediately compromised. Users often reuse passwords, so the breach extends to their accounts on other services.

The correct approach is using password hashing with algorithms specifically designed for this purpose. These algorithms are intentionally slow and include salting.

Bcrypt is the most widely recommended algorithm. It incorporates a salt automatically and has a configurable work factor that can be increased as hardware ge

Question 7

What is your approach to solving a system design interview problem?

Accepted Answer

A structured approach to system design interviews ensures you cover all important aspects while demonstrating clear thinking.

Start by clarifying requirements. Spend the first few minutes asking questions to understand the scope. What are the core features? Who are the users? What scale are we designing for? Are there specific constraints like latency requirements or budget limits? This shows you do not make assumptions and think like a senior engineer.

Next, establish the scale with back-of-envelope calculations. Estimate daily active users, requests per second, storage requirements, an

Question 8

How do you perform back-of-envelope calculations for system design?

Accepted Answer

Back-of-envelope calculations help estimate system requirements and validate design decisions. They do not need to be precise, just reasonable approximations.

Start with useful reference numbers to memorize. One million seconds is roughly eleven days. One billion seconds is roughly thirty-two years. One kilobyte is one thousand bytes. One megabyte is one million bytes. One gigabyte is one billion bytes. Read latency from memory is about one hundred nanoseconds. Read from SSD is about one hundred microseconds. Read from disk is about ten milliseconds. Network round trip within a data center

Question 9

How would you describe your leadership style as a senior engineer?

Accepted Answer

My leadership style blends servant leadership with situational coaching. I focus on enabling others to do their best work rather than directing every detail.

At its core, servant leadership means my primary job is removing obstacles and creating conditions for success. I ask the team what they need, not just what they should do. When someone is blocked by an unclear requirement, I work with stakeholders to clarify it. When tooling slows development, I advocate for improvements.

The situational aspect means adapting my approach based on individual needs and circumstances. A new team membe

Question 10

What are your best practices for conducting effective code reviews?

Accepted Answer

Effective code reviews balance quality assurance with team development and psychological safety.

Review for the right things. Focus on logic correctness, security issues, performance concerns, and maintainability. Automated tools should catch formatting and style issues. Do not nitpick stylistic preferences that are not in the team's standards.

Be timely. Long-pending reviews block progress and frustrate authors. Aim to provide initial feedback within a few hours for small changes, within a day for larger ones. If you cannot review promptly, let the author know so they can find another r

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Topics

Distributed Systems

Architecture & Patterns

Security Deep Dive

System Design Advanced

Team Leadership

Mock Interview

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