[mapme]

The front end apps are not all the same. If you built an app that handles 3 users well do you think it would easily handle 3 billion with no tweaks at any layer (app, framework, OS, network, hardware, edge traffic routing, internal dc network fabric, caching layer, storage for binary/ graph/ KV/ relational, cluster scheduler, security )? Another example, ML backed products (eg. Search, any RecSys) requires tuning features based on product specific needs.

You also end up leaving massive efficiencies on the floor by not hiring more specialists as you scale. This is a good read which explains it in detail https://danluu.com/in-house/

I would also suggest reading their published papers on in house systems to understand the challenges that come with operating at a large scale.

https://news.ycombinator.com/item?id=30940595

I’m sure FB could operate with a range of employees 40k-100k(?), but that number scaling with users is far from surprising.

[milosmns]

You've mostly explained backend-related issues, no?

[mapme]

Yeah, most of that is backend issues. Part of them dictated by product requirements eg. We require serving 5 year old, <4MB photos with 99th percentile latency of 1 second.

Product and UI has its own complexities, but it seems clear each product is unique and would require different logic.

[MichaelZuo]

Then at most 3 people per product frontend would be enough? But the real number is more like 300+, so I can see the parent's point.