Some customers have reported intermittent resolution issues with .io domains. We can confirm that Route 53 DNS services are operating normally at this time and these issues seem to be related to the .io top-level domain provider.
We've investigated the issue and are primarily seeing incorrect responses from two of the .io nameservers: ns-a4.io and ns-a2.io. These nameservers are returning NXDOMAIN intermittently for domains that do exist. As a result, once a resolver receives the erroneous response, it will cache the non-existence for the negative TTL, which for .io is set to 3600 seconds (1 hour).
One suggestion we have is to increase the TTLs for your domains in Route 53 so that the resolvers cache DNS answers for a longer duration.
(Customer support rep name redacted)
Amazon Web Services
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I have noticed the failures occurring moreso in Asia and Russia than in other regions.
At the same time, it looks, there is only one "ns-a3.io" nameserver working for IO domain, at now...
Edit: Looks like .io is managed in London, and their customer service off hours match the downtime.