> 1. I would get a proper SSL cert signed
Uh, how? Are you assuming that a single BGP leak would be enough to cause e.g. a letsencrypt misissuance for the domain? It sounds like (from other comments) they have a global round-robin resolver setup for their DNS challenges.
> 2. Only hijack one of the ranges, and do not respond to other domains (causing SERVFAIL), so other domains will resolve unaffected
I think exactly that's what they did. I saw people posting SERVFAILs during the outage.
They do, and they don't. They have a round robin setup, for which resolver that validates the DNS challenge - however, they do not validate the DNS challenges from several resolvers[1]. So, if that particular resolver got caught in the BGP leak while doing a challenge verification you could get a valid cert.
Lots of ifs and buts - but it is certainly possible.
> I think exactly that's what they did. I saw people posting SERVFAILs during the outage.
Author is suggesting they should be properly resolving the rest of the domains so they wouldn't cause SERVFAILs.
1. I would get a proper SSL cert signed
2. Only hijack one of the ranges, and do not respond to other domains (causing SERVFAIL), so other domains will resolve unaffected, instead of causing a scene (see: https://www.reddit.com/r/sysadmin/comments/8ejrkk/google_dns...)