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Daniel Emod Kovacs for Superbet Engineering

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7 Tips to Crush Your Next System Design Interview

It is no secret that the tech industry is blooming right now. Many big tech companies are expanding at a mind-boggling pace, which of course means a rapid influx of applicants. This leads to a need for optimising and streamlining the interview experience.

We at Superbet invest a lot into making our interviews concise, comprehensive and reproducible, to ensure all applicants get a fair and equal chance.

One of the essential parts of our interview process is the System Design Interview. It is not something we invented, but I think we're pretty good at giving candidates fair, yet challenging problems to think about for this ~1 hour section of our hiring flow. In my first 6 months of working at Superbet as a tech lead, I've conducted more than 20 interviews - the majority of which had been focusing on system design. With that experience in my bag, I'll spoil you with the best 7 pieces of advice I could come up with to help you ace your next system design interview.

During a system design interview you're presented with a technical problem, e.g.: "how would you design an application, like DEV.to?" and your task is to talk the interviewers through your solution while covering a couple of different topic, e.g.: data modelling, services, scaling, frontend, logging and error handling, just to name a few.

1. Understand the Problem

This may sound clichΓ©, but understanding the problem you're presented is going to give you a great advantage. So many candidates rush into trying to pump out a solution as quickly as they humanly can, without taking the time to really try to understand the question or problem in the first place.

Let's examine why system design interviews exist and what we're trying to measure. Contrary to popular belief, after the interview concludes, we don't actually take the plan you've given us and turn it into the next unicorn startup. We're actually okay with you not giving us a full solution. What we're looking for is the way you approach a technical problem and how well you can reason about your decision making.

The skills you will showcase during the system design interview will be able to tell us how well you'll manage problems in all sort of areas of engineering and not just in the specific environment that's presented during the interview.

2. Collect all of the Requirements

A big mistake a lot of good engineers make, when tackling a system design interview is the lack of questions about the problem. We can't really score you on the assumptions you've made during the interview, although they do give us good insight into how your mind works. It's always safer to just take your time and ask all of the questions that come to your mind.

I like to say this phrase when introducing the system design interview to candidates who hadn't had a chance to take part in one yet: "your questions are just as valuable as your answers".

A good rule of thumb is, if you're about to answer a question starting with "it depends", instead, explain that you need further clarification of specific parameters of the problem that will help you inform your decision. For example, don't just assume you can use AWS for everything. Certain countries may have regulations that prohibit businesses in a couple of different sectors from relying on cloud infrastructure and therefore you'd need to take into consideration the use of on-premise solutions if this is the case.

3. Focus on Note Taking

I know I have a horrible short term memory. To help with remembering details I take notes throughout the day and review them regularly. You don't have to have a bad memory to take advantage of note taking. It will not only benefit you in an extremely stressful situation, by taking reliance on your memory out of the equation, but it also helps interviewers by showcasing what information you're focusing on.

Sometimes a system design interview will present you with a complex problem, especially as you climb higher on the engineering ladder. It's okay to lose track during the interview, however, the way you handle the situation or prevent it from happening in the first place is what's really important to us.

If you're sharing your screen during the interview or are doing the interview in person, you will have a way of showing your notes to your interviewers. I recommend making sure they're aware that you're taking notes and ask if they're interested in your notes. Chances are they will be.

4. Use a Visualisation Tool

The result of the system design interview is a snapshot of a working system with explanation of the choices you've made while coming up with the design. One of the biggest challenges for both the interviewers and the candidates is to keep track of the final solution. We always recommend our candidates to use a visualisation tool that can not only help them with an overview of what they have so far, but also to help us see the solution at a bird's eye view.

The tool I recommend using is Draw.io. The disadvantage of it is that there's no live sharing feature, so the only way for us to see your solution is for you to share your screen. Google Docs is also a viable alternative, albeit with limited options when it comes to drawing shapes.

5. Do Not Get Lost in the Details

Your solution should be comprehensive and should cover a wide array of topics of software design. It's also important to discuss edge cases and non-critical system components, e.g.: logging. The number one reason candidates fail to deliver a full solution to the system design interview on time is lack of focus on higher level issues, a.k.a.: getting lost in details.

To make sure you don't lose yourself in the little details of your solution, I recommend the following approach. Instead of picking the area you're most familiar with, and expanding on it horizontally - you should start at the highest possible level. Explain what you expect your application to be able to do and then work your way down into the specifics of each component of the system.

As an interviewer, I want to intervene as little as possible during the interview. I want to keep the candidate talking, without having to guide them. When you get lost in the details, your interviewer has to make a decision to intervene and interrupt the flow or let you talk, but risk you wasting precious time in details that are not required in your solution. The best way to make sure you provide enough detail is to ask before you give your solution.

6. Talk Through Your Process

From my experience, the most successful candidates all have one quality in common. They are vocal. You might be someone who finds it easy to talk through your thinking process, however that isn't true for everybody and I appreciate that. It's something not everyone's good at naturally, however I recommend practicing thinking out loud, while you're preparing for an interview and you'll find it easier to do during your system design interview as well.

Why is this important at all? To be an effective engineer, your communication skills are extremely important. For more junior engineers we want to make sure that you'll be able to ask your more senior teammates for advice when working on your tasks, while as a senior, we're looking for you to be able to jump in and mentor your teammates, as well as take part in discussions about tech.

7. Do Not Be Afraid to Ask for Help

When you're doing your system design interview at Superbet, we'll try to create the atmosphere of a nice open-ended discussion between tech enthusiasts. As such, we'll be open to answering any and all of the questions you may come up with during the interview.

Have you ever wanted to say during an interview: "I'd just Google x and y"?

On a system design interview it's okay not to know the exact technology or library that you'd use for a solution. In the real world you will be able to get help with all of that, whether it be reading documentation or looking the problem up on StackOverflow.

"I'd use Redis, because I don't have to worry about persistence or memory use, but I need very quick reads and a way to publish changes as they happen" scores just as well as "I'd use an in-memory database, because I don't have to worry about memory and they have quicker access speeds. If it's got built in pub/sub, it's even better. Can you suggest such a database?". Remember, we're interested in your reasoning above all and if the actual answer is just a Google search away, we'll be happy to help you out with it.


Conclusion

If you haven't been in a system design interview or are looking to improve the outcome of your next one, hopefully my tips will get you there. Remember, your mileage may vary. Not everybody does interviews the same way, so if you want to be safe, you can use all of the above in your interview at Superbet. You can find a link to our open positions page on our engineering website.

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