[mgraczyk]

I ask a lot of system design interviews based on Facebook's products. What I look for is the ability to propose something simple, proposing the right metrics and data collection to understand scaling needs, then making reasonable guesses about which parts of the system need to scale. PHP + MySQL + Memcache is great until you also need to do ML inference (high CPU/GPU load), need to store user-uploaded video, or want to stream new content to users in near realtime (live comments).

They key is to add the minimum amount of "stuff" to a simple design to convincingly scale for some new hypothetical need.