Discord Senior Software Engineer Interview Questions

1.Walk me through a time you had to debug or optimize a system where latency was critical. What was the latency requirement, how did you approach the problem, and what was the outcome?

2.Tell me about the most complex debugging problem you've solved in the last year. What resources did you use to figure it out?

3.Tell me about a project where you had to work across multiple programming languages or runtimes. What languages were involved, why was this necessary, and what challenges did you face?

4.Describe a time you had to scale a system to handle significantly more load. What was the initial capacity, what did you scale it to, and what was your approach?

5.Walk me through a time you inherited or worked on a system that was difficult to test. What made it hard to test, and how did you improve it?

6.Describe a time you had to make real-time performance tradeoffs in a system design. What were the competing priorities, and how did you decide what to optimize for?

7.Write a function that determines if a Discord user can join a voice channel, given the channel's user limit, current occupants, and the user's permissions.

8.Design a system to track which Discord features each user has tried, so we can show personalized onboarding tips. This needs to work across web, desktop, and mobile clients.

9.A Discord bot developer reports their bot is randomly missing messages in high-traffic servers. The bot processes about 1000 messages per second and uses our Gateway WebSocket API. What could be causing this and how would you investigate?

10.You need to add a new field to user profiles that will be displayed on every message in Discord. This data needs to be available instantly when rendering messages. How would you architect this?

11.You're building a feature that needs to coordinate state across multiple Discord servers in real-time. Each server runs on a different BEAM node. How would you approach this coordination problem?

12.You're tasked with integrating a Rust-based audio processing library into Discord's Elixir voice infrastructure using Rustler NIFs. Walk me through your implementation approach.

13.Design a system that lets Discord bot developers test their bots against realistic message traffic before deploying to production servers. The system needs to simulate message patterns from servers with 100K+ active users.

14.You need to build a system that automatically moderates voice channels for harmful audio content across Discord's voice infrastructure. How would you design this to work at Discord's scale without adding perceptible latency to voice calls?

15.Design the backend system for Discord Activities - the games and apps that run inside voice channels. This needs to sync game state in real-time across all participants while handling players joining and leaving mid-session.

16.Build a system to detect and prevent Discord server raids - coordinated attacks where hundreds of accounts join a server simultaneously to spam or disrupt the community. The system needs to work in real-time as users are joining.

17.Design a system that automatically generates suggested Discord server rules based on the community's conversation patterns, member behavior, and moderation actions. The suggestions should help new communities establish healthy norms before problems arise.

18.You're building a feature that lets Discord server owners create custom slash commands that can read and write to external APIs. Design the execution environment and security model to safely run untrusted code at Discord's scale.

19.Tell me about a time you had to convince a skeptical engineer or team to adopt a new technology or approach. What was your strategy and how did it play out?

20.Describe a time you had to support a teammate through a significant technical or professional challenge. What was your approach and what did you learn?

21.Describe a situation where you had to coordinate work across multiple teams to ship a feature. What made the coordination challenging and how did you handle it?

22.Walk me through a time when you had to make a significant architectural decision that other engineers disagreed with. How did you build consensus and what was the outcome?

23.Tell me about a time you identified that your team was working on the wrong thing. How did you redirect the effort and what resistance did you face?

24.Tell me about a time you had to influence a product or design decision based on technical constraints that weren't obvious to non-engineers. How did you communicate the issue?

25.Estimate how many messages per second Discord needs to handle globally during peak hours. Walk me through your assumptions about user behavior and message patterns.

26.A Discord server with 500K members is seeing 60% of new users leave within their first week. The server owner asks for help analyzing why. Walk me through how you'd investigate this retention problem.

27.A gaming community reports that their Discord bot stops responding during tournament streams when viewership spikes. The bot handles tournament brackets and live score updates. How would you investigate this?

28.Discord wants to add a feature that suggests optimal server categories and channels when users create new servers. Estimate how much compute this recommendation engine would need and what data it should analyze.

29.You're investigating why Discord's message search is returning stale results for some users. Active messages aren't appearing in search for up to 30 minutes. How would you approach this systematically?

30.Discord is considering adding end-to-end encryption for voice calls. Estimate the additional bandwidth and compute costs this would add globally. What are your key assumptions?