I'd like to start using Cloudflare's Anycast DNS for my website, which also includes their CDN. However, I see they've had outages. I looked into Akamai Edge DNS, and it too has gone down. I'm wondering, then, if it's possible to have multiple authoritative name server providers. On my registrar's site, I can enter up to 6 authoritative name servers. What would happen if I entered 2 from one provider, and 2 from another? I realize I'd need to maintain the DNS records at both providers, which isn't a problem. Do authoritative name servers get selected at random from the TLD's list for a name, or does the first authoritative name server get tried, and if it fails, the second would be tried, etc.? Does anything stop this approach from working?
Thanks in advance.
1 Answer
Authoritative servers are selected at random. DNS records are unordered, unless they explicitly have a priority field (e.g. like in MX or SRV records).
There should be no problems as long as all nameservers answer with the correct data. (This means you probably won't be able to use Cloudflare CDN easily, as it relies on replacing your A/AAAA records with its own – deploying the same records to another provider will bypass the CDN.)
The zone must be configured for DNSSEC in the same way (e.g. either all providers serving signed zoned or all unsigned).
superuser.com uses AWS and Google Domains at the same time. I think they had a blog post at StackOverflow about doing this for redundancy.
Before worldwide anycast cloud CDNs became the norm, it used to be quite common to use someone else's nameservers as backup, e.g. configuring Linode DNS to replicate from your own master authoritative server. This might still be possible if both sides support the standard "zone transfer" replication mechanism (AXFR), without having to manually keep them in sync.
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