What should you do if you’re asked to design a system you’re not familiar with during an interview?

Facing a system design interview question about a product or system you’ve never heard of can be intimidating. You might be thinking, “How can I design something I know nothing about?” The good news is that interviewers don’t expect a perfect solution or encyclopedic knowledge of every system. Instead, they care about your approach and problem-solving process. In this beginner-friendly guide, we’ll walk through exactly how to handle an unfamiliar system design prompt with confidence. You’ll learn practical strategies (think technical interview tips and system design interview preparation tactics) to stay calm, clarify what’s needed, apply solid software design principles, and design a high-level architecture on the fly. Let’s break it down step by step.

Understand the Interviewer’s Goal

First, remember why companies ask system design questions. It’s not to see if you memorized the architecture of “Some Obscure Service 101.” They want to see how you think through problems and handle ambiguity. In a real job, you often have to design features or systems you’ve never built before. Interviewers simulate that scenario to evaluate your problem-solving framework and communication skills, not just your recall of facts. In fact, even if the system is totally unfamiliar, a strong candidate can still demonstrate good engineering thinking. For example, one experienced engineer notes that you should still be able to gather requirements, break the problem into components, and discuss relevant concepts for virtually any system design question. So, take heart: you’re not expected to produce a fully-fledged solution on the spot. Your interviewer is assessing how you approach an open-ended challenge. With that mindset, let’s move on to the strategy.

Stay Calm and Plan Your Approach

When you get a design prompt you’ve never seen, the first step is to stay calm. It’s natural to feel a jolt of panic, but taking a deep breath will help you think clearly. Remember, composure is key. Instead of blurting out the first idea that comes to mind, let the interviewer know you’d like to work through the problem with a structured game plan. This shows confidence and organization.

Outline a framework before diving in: Explain that you’ll start by clarifying the requirements, then sketch out a high-level design, discuss components, consider trade-offs, etc. Interviewers appreciate a methodical approach over someone jumping straight into the weeds. It’s perfectly fine to take a minute to jot down a quick plan or just collect your thoughts.

Here are some initial steps to set the right tone when facing an unfamiliar design problem:

• Restate the problem in your own words: Begin by summarizing what you understand the system needs to do. For example, “Okay, so we need to design a video streaming service for X scenario…” This ensures you and the interviewer are on the same page and gives you a moment to think.
• Outline your approach upfront: Signal that you have a plan. You might say, “First, I’ll clarify the requirements and constraints. Then I’ll identify the core components of the system and sketch a high-level architecture. Finally, I’ll discuss some key design decisions and their trade-offs.” This “framework talk” demonstrates you’re approaching it systematically.
• Stay positive and curious: Instead of silently freaking out “I have no idea what to do,” treat it like a collaborative brainstorming session. Adopting a confident, curious mindset (e.g. “This is interesting — let’s figure it out”) will make you come across as composed and solution-oriented. Remember, there’s often no single “right” answer in system design interviews – what matters is that you show thought, planning, and consideration of alternatives.

By starting off calm and structured, you set a great foundation. Interviewers will see that you can handle pressure and think logically, even when the problem is unfamiliar.

Ask Clarifying Questions to Define the Scope

Once you’ve outlined a general approach, begin with clarifying questions. Unfamiliar or not, every system design problem has requirements and constraints you need to nail down. Don’t assume anything that hasn’t been stated – instead, ask questions to fill in the blanks. This step is crucial to avoid solving the wrong problem or going off on an irrelevant tangent.

Start by figuring out the core purpose and scope of the system:

• What are the goals of the system? Identify what the system needs to accomplish. For example, is the interviewer asking for a high-level architecture overview or a deep dive into one component? The way the question is phrased might hint at this, but it’s wise to confirm.
• Who are the users and use cases? Ask about the primary users or actors and what they need to do with this system. Knowing the typical actions or features (e.g. “Users can upload and share photos” or “Devices send sensor data every minute”) will focus your design on the right functionality.
• What are the functional requirements? Pin down the key features or operations the system must support. For instance, if it’s a chat application, does it need search capability or just basic send/receive? If it’s a ride-sharing system, do we need real-time driver tracking, payments, ratings, etc.? Getting these details helps prevent unpleasant surprises later.
• What are the expected scale and constraints? Always ask about scale: How many users or requests are we talking about? Designing for 1,000 daily users vs. 100 million monthly users can be very different! Clarify any numbers like “transactions per second” or data size that the system should handle. Also, ask about performance targets (latency requirements) or uptime needs. For example, is 99.9% availability (minimal downtime) a goal? Any specific response time needed (like “every request should be under 200ms”)? These constraints will guide your design choices.
• Any technology preferences or other constraints? Sometimes the interviewer might mention, “Assume we must use a NoSQL database,” or “Cost is not a concern,” or “Security is very important.” If they haven’t stated such things, it’s okay to ask if there are any constraints or assumptions you should be aware of (for instance, regulatory compliance for a healthcare system, or budget limits, etc.). This shows you’re thorough.

By asking these clarifying questions, you’ll transform a fuzzy problem into a clearer picture. Plus, it turns the interview into a two-way conversation rather than a one-sided interrogation, which can help calm your nerves. Interviewers actually appreciate this – it shows you think like an engineer who gathers requirements before jumping to solutions. Be sure to listen carefully to the answers, as they will heavily influence the direction of your design. Jot down the key requirements and constraints as the interviewer answers; these become your checklist for the next steps.

Define the Requirements and Constraints Out Loud

After you’ve gathered enough information, take a moment to summarize the system’s requirements and constraints out loud. This serves two purposes: it confirms to the interviewer that you understand the problem, and it creates a roadmap for your solution. It’s often helpful to categorize the requirements into functional and non-functional:

• Functional Requirements: These describe what the system should do – the features and behaviors. List the core features the interviewer mentioned or you inferred. For example, if you need to design a URL shortener, your functional requirements might be: the system should generate short URLs, redirect users to the original URL when they hit the short link, and possibly track click analytics. If any features are explicitly out-of-scope, state those too (e.g. “We won’t worry about user accounts or login, we’ll assume it’s a public service”). This demonstrates focus on the core problem.
• Non-Functional Requirements (Constraints): These are the quality attributes and limitations of the system – essentially how the system should perform. They often include scale (e.g. “must handle 10 million requests per day”), performance (e.g. “responses should be under 200ms”), availability/reliability targets (e.g. “99.99% uptime, no single point of failure”), data storage needs (e.g. how much data and retention period), and consistency requirements (e.g. “is eventual consistency okay, or do we need strict consistency?”). Mention any such constraints the interviewer gave you. For instance, “Since we expect up to 50k concurrent users, I’ll need to design with scalability in mind” or “Because this is a banking system, consistency and security will be top priorities.” Align your upcoming design with these points.

By clearly stating requirements, you not only prove your understanding but also set yourself up to design in a structured way. It’s like writing down the problem statement and design criteria before trying to solve it – a sign of a thoughtful engineer. Interviewers often nod along or correct you if you missed something at this stage. Once you get the nod, you’re ready for the fun part: designing the system!

Outline a High-Level System Architecture

Now it’s time to map out the high-level architecture of your solution. Even if the domain is unfamiliar, many systems share common building blocks. Start by identifying the core components or subsystems you’ll need. Think of how information will flow through the system from the user’s action to the result. This is where you decide what pieces make up your design.

A useful approach is to talk through the request lifecycle. For example, describe: “The user’s request comes in through X, then goes to Y, which processes it and interacts with Z to store/retrieve data.” By doing so, you can naturally enumerate components along the way. Here are some common components to consider (you’ll tailor this list to the specific question, of course):

• Client Interface: How do users interact with the system? It could be a mobile app, web browser, or perhaps IoT devices. Mentioning the client helps set the context (e.g. “Users will use a mobile app that hits our backend APIs”).
• Application Server / API Layer: Most systems have a backend service that handles requests, executes business logic, and orchestrates between other components. Often, you’ll propose a layer of web or application servers to handle incoming user requests. For instance, “We’ll have an application server (or multiple, behind a load balancer) that receives API calls from the client, processes them, and issues database queries or calls other services.”
• Database / Storage: Almost every system needs to store data. Choose an appropriate storage based on the requirements. If we expect complex relational queries or transactions, mention a SQL database; if we need to scale massively or store unstructured data, a NoSQL or distributed database might be better. E.g., “User info and posts will be stored in a relational database for consistency, while images will go to a blob storage (like AWS S3)”.
• Load Balancer: If high traffic or high availability is a concern, propose a load balancer to distribute traffic across multiple servers. For example, “A load balancer in front of the app servers will help us handle more users and avoid any single server becoming a bottleneck.” This is a quick way to address scalability and reliability.
• Cache: Caching frequently accessed data in memory (using something like Redis or Memcached) can drastically improve performance. If the problem hints at heavy read load or low-latency needs, mention a cache. E.g., “We can use a cache to store popular items or results so we don’t hit the database for every request, keeping response times under 200ms as required.”
• Asynchronous Workers / Queue (if relevant): Many large systems use background workers or message queues for tasks that don’t need to happen during the user request, such as sending emails, processing images, or heavy computations. If applicable, you can suggest, “I’d add a message queue and a worker service for handling tasks like X, so the user request isn’t delayed by that processing.”

Not every design interview question will need all of these components, but these are building blocks to think about. The key is to break the system into manageable pieces instead of one big black box. For an unfamiliar system, this strategy is a lifesaver: it lets you tackle one piece at a time using familiar concepts (like databases, caches, etc.), rather than feeling overwhelmed by the system as a whole. As one Stack Exchange user advises, even with a totally unknown system, you should demonstrate the ability to gather requirements and divide the problem into front-end, back-end, database, etc., as needed.

While outlining your architecture, briefly mention the role of each component and why it’s there. For example, you might say: “We’ll use a REST API server to handle client requests, a load balancer to spread traffic, a primary database for persistent storage of user and transaction data, and an in-memory cache (like Redis) to cache hot data and reduce latency.” This paints a clear picture of your design. You’re effectively sketching a mental diagram for the interviewer.

Don’t worry about drawing actual diagrams unless you’re using a virtual whiteboard or the interviewer asks – describing it in words is usually enough in a conversational setting. As you lay out the pieces, the interviewer may ask questions or give feedback. This is normal and can even guide you toward what aspect they care about most (for instance, they might zoom in on the database choice or how to handle a specific bottleneck).

By the end of this step, you should have described a high-level solution: the major components and how data flows between them. You’ve turned that scary unknown problem into a set of familiar parts: perhaps a client, some servers, a database, etc., working together. That’s a huge win! Now it’s time to show off your decision-making and trade-off analysis.

Discuss Design Decisions and Trade-Offs

A great way to stand out in a system design interview is to explain the rationale behind your choices and consider alternatives. There is rarely one “correct” architecture; every choice has pros and cons. Showing that you’re aware of these trade-offs indicates maturity and depth of knowledge. In fact, strong candidates will often bring up a couple of possible approaches and then pick one, explaining why. You can do this even if you’re not fully confident – it demonstrates critical thinking.

Here are some areas where you might discuss trade-offs or alternatives in your design:

• Database Selection (SQL vs NoSQL): If data storage is a part of the design, mention why you prefer one over the other based on requirements. For example, “For a social network feed system, a NoSQL database might make sense to easily scale horizontally and handle a high volume of simple reads/writes. However, if we needed complex transactions (say for a banking system), an SQL database would be better for consistency.” This shows you understand how the choice aligns with system needs.
• Consistency vs Availability: In distributed systems, there’s often a trade-off between ensuring data is always consistent and keeping the system highly available (think of the CAP theorem). If relevant, mention which is more important for this system. “Since this is a messaging system, a little delay (eventual consistency) is okay if it means the system stays up during network partitions. We’d prioritize availability and performance over strict consistency for, say, showing ‘likes’ on a post.” On the other hand, if it’s something like a bank account balance, you’d explain consistency is critical.
• Use of Caching/CDNs: You might note the benefit of caching versus the complexity it adds. “We could introduce a CDN or cache layer for faster content delivery. The upside is speed, but the trade-off is cache invalidation complexity – we have to ensure users don’t see stale data. Given the requirement for low latency on a global scale, this trade-off is worth it.” This kind of reasoning highlights that you’re thinking about performance optimizations and their implications.
• Monolithic vs Microservices Architecture: If it comes up, you can talk about structuring the system as a single service vs splitting into multiple specialized services. “To keep it simple initially, I’d design it as a well-organized monolithic application. Since our time is limited (in the interview and likely in a real scenario MVP), this avoids the complexity of managing multiple services. However, I’d mention that as the system grows, we could later break out critical components into microservices for independent scaling (for example, a separate service just for the search functionality if that becomes a bottleneck).” This shows you are mindful of evolution and scalability without over-engineering from the start.

As you discuss each major decision, be sure to tie it back to the requirements. For instance, if the requirement is “handle 1 million users,” you’d justify using a load balancer and multiple servers for scalability. If the requirement is “99.99% uptime,” you’d mention redundancy and avoiding single points of failure (like having replicas of the database, using multiple availability zones, etc.). This assures the interviewer that your design isn’t random but is grounded in the problem’s needs.

It’s also perfectly fine to acknowledge areas you’re unsure about or ask the interviewer if they have a preference. For example, if you’re not too familiar with a specific technology, you could say, “One option here is to use Cassandra for the time-series data – I haven’t used it in depth, but it’s known to handle large write throughput well. Alternatively, a traditional SQL database with partitioning might also work. Given our scale requirements, a NoSQL solution seems safer for scaling writes.” Being honest about your assumptions and then reasoning through them is much better than bluffing. Many interviewers appreciate honesty and will either confirm your direction or give a hint. In fact, if a candidate encounters an unfamiliar concept, being upfront about it and then demonstrating how you’d reason through it is a solid approach.

Finally, throughout your design explanation, communicate your thought process clearly. Keep talking as you think, so the interviewer isn’t left guessing. For example, as you consider a trade-off out loud, it might sound like, “We could go with Solution A for simplicity, but then we might have a single point of failure here... If we do Solution B, it’s more complex but handles failures better. Given the time, I’d lean towards A with a note on how to improve it later.” This kind of reasoning out loud lets the interviewer see your analytical skills in action. It also mirrors real-world engineering discussions, which is exactly what the interviewer wants to envision: how you’d handle designing something new on the job.

Practice and Prepare for the Unexpected

Handling an unfamiliar design question is much easier if you’ve practiced system design fundamentals ahead of time. While you can’t anticipate every question, you can build a toolkit of principles and example systems to draw from. Here are some tips to prepare (especially if you feel you have no experience):

• Learn the fundamentals of scalable systems: Make sure you understand core concepts like load balancing, sharding, caching, database indexing, message queues, etc. These are the building blocks that show up in many designs. DesignGurus offers a fantastic beginner-friendly course called Grokking System Design Fundamentals that covers these basics (caching, load balancers, data partitioning, and more) in a digestible way. Having these principles at your fingertips will let you confidently propose components even for a system you’ve never seen before.
• Study common system design examples: It’s helpful to walk through a few classic designs (like a URL shortener, a social media news feed, an online chat system, etc.) to see how engineers break them down. The Grokking the System Design Interview course is a popular resource that takes you through many real-world design case studies step-by-step. By seeing those examples, you’ll start recognizing patterns (for instance, almost every large system needs a database + cache combo, or how different systems handle spikes in traffic).
• Practice with mock interviews or scenarios: Try doing a mock interview with a friend or even by yourself. Take a random system (it could be “design a smart fridge” or “design a traffic control system”) and give yourself 30 minutes to outline a solution. The goal isn’t to become an expert in refrigerators or traffic algorithms in one go – it’s to get comfortable with the process: asking questions, defining requirements, outlining components, etc. Mock interview practice can greatly improve your confidence and reveal areas to learn more about. You can also use online platforms or forums where people discuss system design problems to refine your approach.
• Use Q&A resources for specific advice: Check out Q&A articles and forums for tips on handling unfamiliar questions. For example, we have an in-depth Q&A on how to handle unfamiliar system design interview questions (the very scenario we’re discussing) and another on the best way to prepare for a system design interview with no experience. These resources reiterate many of the strategies here – like starting broad then diving deeper, having a clear framework, and practicing incrementally. Sometimes reading others’ experiences and solutions can provide new insights or at least reassure you that you’re on the right track.

Remember, system design is a skill, and like any skill, you get better with practice. Even if you’re a newbie, by consistently learning and practicing, you’ll quickly improve your ability to think through unfamiliar design problems. One Reddit user recommended starting with fundamentals and case studies – exactly the approach we just outlined (courses + practice). Over time, you’ll find that no system design question feels truly “unfamiliar”: you’ll have seen something similar before, or you’ll at least know which questions to ask and which components to consider.

Conclusion

Walking into a system design interview without knowing the domain can feel daunting, but it’s also a chance to shine by showcasing your structured thinking and adaptability. By staying calm, asking smart questions, and breaking the problem into familiar pieces, you can navigate even the most unfamiliar scenarios. Always keep the big picture in mind – what are we trying to achieve and what constraints are we working under – and let that guide your architecture decisions. We’ve discussed how focusing on fundamentals and using a clear framework can turn a curveball question into a manageable discussion.

In the end, system design interviews are as much about communication and approach as they are about the final design. So next time you’re asked to design “The Next Big Thing” that you’ve never even imagined, take a deep breath and dive in step by step. You’ve got this! And if you want to keep improving, consider exploring more resources or signing up at DesignGurus.io for courses like Grokking the System Design Interview and System Design Fundamentals. They’ll help you practice and prepare so that even the trickiest questions feel a lot more familiar. Good luck, and happy designing!

FAQs: Handling Unfamiliar System Design Questions