I'm a former WhatsApp server engineer[1]. WhatsApp primarily moved from bare metal hosting running FreeBSD to Facebook's owned and operating containerized management system which incidentally runs Linux.
We did not make a technical choice to abandon FreeBSD in favor or something else, we made an organizational choice to abandon external hosting in favor of owned and operated hosting which required a lot of technical changes, one of which was switching operating systems.
About half of the server engineering team pre-acquisition was former Yahoo employees, and we had seen what happens when an acquired company does not assimilate the acquirer's basic tech stack --- every issue with hardware or software first has to go through the triage step of is it broken because you're not running the company's OS and the company's package manager and the company's monitoring service and whatever else. That's not a great position to be in when you're trying to run a reliable service, so we decided it would be better to accept Facebook's foundational tech stack and hope the benefits outweighed the costs.
[1] As such, I usually recuse myself from discussions of WhatsApp and Facebook, I'm certainly not authorized to speak on behalf of either; my opinions are my own, etc.
I'm a former WhatsApp server engineer[1]. WhatsApp primarily moved from bare metal hosting running FreeBSD to Facebook's owned and operating containerized management system which incidentally runs Linux.
We did not make a technical choice to abandon FreeBSD in favor or something else, we made an organizational choice to abandon external hosting in favor of owned and operated hosting which required a lot of technical changes, one of which was switching operating systems.
About half of the server engineering team pre-acquisition was former Yahoo employees, and we had seen what happens when an acquired company does not assimilate the acquirer's basic tech stack --- every issue with hardware or software first has to go through the triage step of is it broken because you're not running the company's OS and the company's package manager and the company's monitoring service and whatever else. That's not a great position to be in when you're trying to run a reliable service, so we decided it would be better to accept Facebook's foundational tech stack and hope the benefits outweighed the costs.
[1] As such, I usually recuse myself from discussions of WhatsApp and Facebook, I'm certainly not authorized to speak on behalf of either; my opinions are my own, etc.