Video Calls (Zoom / Google Meet: SFUs, Simulcast, Bad Networks)
Design a video calling system like Zoom or Google Meet: SFU media servers, simulcast, WebRTC, TURN, bad networks, cascading regions and large webinars.
The Engineering Career Operating System
More than interview prep. Your path forks at Senior, into building (IC) or leading (management). Pick a goal, see the real bar, and follow the exact path to get there.
Built by Staff Engineers, Principal Engineers, and Engineering Leaders who've built systems, led teams, and hired engineers.
The bar for each level is the real one, not generic advice.
You add one Redis node to a 10-node cache. Your app picks a node with hash(key) % N. Hit rate drops from 95% to 9% and Postgres is overloaded, though no key was deleted.
Why did adding one node empty the cache?
Pick one. If it is wrong, you will see why, and you can try again.
Pick a level and be honest. Could you actually answer each of these out loud, right now? If several are shaky, that is the gap, and that is exactly what the path is for.
The bar: Design across services, make and defend trade-offs, and lead a design review.
If several are shaky, you are probably not there yet. Here is the path.
See the Senior Engineer pathWhether you are building LLM systems or getting grilled on them, go deep: the foundations, the engineering, the security, and the AI system design round. Read a full lesson free before you decide.
Now we also crack a few walnuts out loud, on video. Everything here stays right where it is.