Wait... is @1111Resolver serving the new CNAME I created at @DreamHost faster than the authoritative name server at DreamHost?
Or am I seeing a side effect of caching?pic.twitter.com/JPpJJAL7m4
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It's super obnoxious for certificate issuance. GitHub might resolve via ns2 or ns3 and think that the CNAME is provisioned and request a certificate, but when Let's Encrypt checks they use ns1 and consequentially reject the request.
Yeah, I'm partially trying this out to get a feel for issues like that. This one seems to have worked, though! 
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