> And what I’m getting to is that yes, they had 50 engineers in their pay roll, but many more supporting various SaaS products and infrastructure they use and pay for.
I was at WhatsApp from 2011 to 2019.
Hardware was outsourced to SoftLayer, of course. I think they had a sizable operation, but if you move that in house, you've got a team of 4ish for 24x7 colo work (we were only in one location for an embarassing amount of time), plus a networking person, and maybe a manager. We certainly got better service with SoftLayer's larger team including ease of getting more servers, but we would have had better visibility in house, so it's a tradeoff. Softlayer's staff was probably smaller than the combined staff if all of their major customers in-sourced, anyway.
Other than that, we used multiple providers for SMS and voice verification; some of whom have a lot of staff. You need more staff for this, IMHO, because in addition to 24x7 coverage, you also need to arrange connectivity with carriers in all timezones and all languages. But some of the companies we used seemed pretty small, so I dunno.
We were using Zendesk in our customer service system after growing out of Gmail and before in-sourcing it after aquisition, and Dyn for DNS (which doesn't take much staff to insource).
What other SaaS do you think we used? Do you want to count the OS app stores and push services? Maybe payments while that lasted? G Suite for corporate email when forwarding to personal mail became too silly?
We self-hosted our code repository and bug tracker.