IIRC that was a DNS issue, which is why it took down all the Meta services. In other words, the WhatApps Erlang servers were probably happily humming away.
Although, actually, in this case, it was BGP. The haiku works for both. Now, because (Facebook's) BGP was broken, the DNS servers were unavailable, but WhatsApp will work without DNS (I used to work there, and helped make sure this feature continued during the move to Facebook's infrastructure). Usually, it's your network's DNS that's failing, but sometimes it's WhatsApp's DNS that's failing; either way, having IPs to connect to is sure handy.
It's not DNS
There's no way it's DNS
It was DNS
Although, actually, in this case, it was BGP. The haiku works for both. Now, because (Facebook's) BGP was broken, the DNS servers were unavailable, but WhatsApp will work without DNS (I used to work there, and helped make sure this feature continued during the move to Facebook's infrastructure). Usually, it's your network's DNS that's failing, but sometimes it's WhatsApp's DNS that's failing; either way, having IPs to connect to is sure handy.