Getting Ready for the System Design Interview

A System Design Interview evaluates your ability to build robust, scalable systems. Unlike coding interviews, which typically seek a single correct solution, System Design involves open-ended discussions with multiple valid approaches.

Many engineers struggle with these interviews because they haven’t worked on large-scale systems. A structured approach makes preparation much easier. After running hundreds of System Design interviews, I’ve found there are a few repeatable patterns that consistently work. With practice, you can approach most design questions methodically instead of improvising. These interviews test how you reason about tradeoffs, not just what you know. Success comes from clarifying the problem, breaking it down, and proposing a solution you can justify.

The author’s background in System Design

I’m Fahim ul Haq, co-founder of Educative and co-author of this course. In April 2008, I joined an internal Microsoft team building a distributed storage system. Amazon had launched S3 in 2006, and Google introduced App Engine the same month I joined the team. We were operating at the beginning of the cloud infrastructure race. Less than two years later, that project became Microsoft Azure.

When I moved from the Exchange team to Azure, I understood storage systems but not globally distributed architectures. I learned distributed systems in production. That experience shaped how I approach System Design. These concepts now show up regularly in System Design interviews and in day-to-day engineering decisions.

What I learned through hundreds of System Design Interviews

After running hundreds of interview loops at Facebook, Microsoft, and Educative, two skills consistently stood out:

1. Building a strong grasp of distributed systems fundamentals and applying them to real-world problems.

2. Understanding how candidates are evaluated during System Design interviews.

Counterintuitively, companies do not expect you to have built massive systems previously. Interviewers know this experience is rare. Instead, they test your ability to apply fundamental principles to new problems.

Note: The key is to prepare for the System Design interview with the intent to apply that knowledge.

This course is useful for both interview candidates and practicing engineers. It breaks down the interview format and focuses on techniques you can also apply in production systems.

How do System Design interviews differ from other interviews?

You must approach System Design Interviews strategically. Unlike coding interviews, they rarely require writing code.

System Design Interviews operate at a high level of abstraction. You must define requirements and map them to computational components and communication protocols.

How do we tackle a design question?

Design questions are intentionally vague and open-ended to mimic real-world business ambiguity.

Interviewers often ask you to design a well-known product, such as WhatsApp. WhatsApp has a large feature set, but you shouldn’t try to design everything in an interview. Trying to cover every feature is a mistake because:

1. You have limited time.

2. Designing core functionalities is sufficient to demonstrate problem-solving skills.

Inform the interviewer that you will focus on specific core features. If they object, adjust your plan accordingly.

Follow these best practices during the interview:

• Ask clarifying questions to solidify requirements.

• Scope the problem to ensure you can solve it within the 35–40 minute time frame.

• Communicate constantly. Engage the interviewer to validate your thought process; do not design in silence.

Present the high-level design

High-level components include frontends, load balancers, caches, and data processing units. Your design explains how these components fit together.

Architectural diagrams often represent components as boxes. The arrows between them represent communication protocols and data flow.

Possible questions for every System Design interview

Interviews often explore how a design evolves as traffic or data grows by orders of magnitude. A design that works for 1,000 users may fail at 1,000,000.

Scaling is rarely linear. You must anticipate bottlenecks and modify the architecture as demands increase.

Design challenges

Systems inevitably change and break. Remember:

• There is no single correct solution.

• Success depends on your assumptions.

The responsibility of the designer

Designers must ensure fault tolerance. As modern systems rely on millions of off-the-shelf components, failures are guaranteed. Your design must handle these failures gracefully without impacting the user.

Who is eligible for a System Design interview?

Mid-to-senior level candidates (2+ years of experience) typically face at least one System Design interview. Senior roles often include multiple System Design rounds. Many junior roles now include system design questions to evaluate problem-solving and architectural thinking. For example, Netflix includes System Design interviews at every level.

Theory and practice

Most of the theory of System Design comes from the domain of distributed systems. Getting a refresher on these concepts is highly recommended. Educative has an excellent course on distributed systems that we can use to refresh our knowledge of distributed systems concepts.

Distributed systems rely on mature software principles:

• Robustness (maintaining operations during a crisis)

• Scalability

• Availability

• Performance

• Extensibility

• Resiliency (returning to normal operations quickly after disruption)

These terms create a shared vocabulary between you and the interviewer.

For example, discussing the trade-off between availability and consistency during network failures (citing the CAP theorem) demonstrates both theoretical knowledge and practical application.

When does the System Design interview occur in the hiring process?

At FAANG+ companies (Facebook, Apple, Amazon, Netflix, Google, Microsoft), the System Design Interview typically follows coding rounds and precedes behavioral interviews. A typical timeline is depicted below:

Remember: Your goal is to actively demonstrate your skills to the interviewer.