alt Hacker NewsI am reminded of the warning that zonemaster gives about putting your domain name servers on a single AS, as is common practice for many larger providers. A lot of people do not want others to see this as a problem since a single AS is a convenient configuration for routing, but it has the downside of being a single point of failure.
Building redundant infrastructure that can withstand BGP and DNS configuration mistakes are not that simple but it can be done.
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As the CPU/RAM resources to run an authoritative-only slave nameserver for a few domains are extremely minimal (mine run at a unix load of 0.01), it's a very wise idea to put your ns3 or something at a totally different service provider on another continent. It costs less than a cup of coffee per month.
On Google cloud it's always four nameservers like
ns-cloud-c1.googledomains.com
ns-cloud-c2.googledomains.com
ns-cloud-c3.googledomains.com
ns-cloud-c4.googledomains.com
It's simple enough to get a secondary DNS server somewhere and put it on $5/month VPS. I use BIND and DNS replication (AXFR/IXFR) handles it.