At my company (getstream.io) we've been having issues when resolving our domains randomly. After some more investigation it seems some .io nameservers are returning bad results. Specifically ns-a2.io and ns-a4.io. A correct result for crates.io looks like this:

  $ dig crates.io @ns-a1.io +norecurse

  ; <<>> DiG 9.11.2 <<>> crates.io @ns-a1.io +norecurse
  ;; global options: +cmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18874
  ;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 3, 
  ADDITIONAL: 1

  ;; OPT PSEUDOSECTION:
  ; EDNS: version: 0, flags:; udp: 4096
  ;; QUESTION SECTION:
  ;crates.io.			IN	A

  ;; AUTHORITY SECTION:
  crates.io.		86400	IN	NS	dns3.easydns.ca.
  crates.io.		86400	IN	NS	dns1.easydns.com.
  crates.io.		86400	IN	NS	dns2.easydns.net.

  ;; Query time: 83 msec
  ;; SERVER: 194.0.1.1#53(194.0.1.1)
  ;; WHEN: Wed Sep 20 15:33:13 CEST 2017
  ;; MSG SIZE  rcvd: 127

A bad one looks like the following:

  dig crates.io @ns-a4.io +norecurse

  ; <<>> DiG 9.11.2 <<>> crates.io @ns-a4.io +norecurse
  ;; global options: +cmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 43223
  ;; flags: qr aa; QUERY: 1, ANSWER: 0, AUTHORITY: 1, 
  ADDITIONAL: 1

  ;; OPT PSEUDOSECTION:
  ; EDNS: version: 0, flags:; udp: 4096
  ;; QUESTION SECTION:
  ;crates.io.			IN	A

  ;; AUTHORITY SECTION:
  io.			900	IN	SOA	a0.nic.io. noc.afilias-nst.info. 1497256201 10800 3600 2764800 900

  ;; Query time: 10 msec
  ;; SERVER: 74.116.179.1#53(74.116.179.1)
  ;; WHEN: Wed Sep 20 15:34:59 CEST 2017
  ;; MSG SIZE  rcvd: 105

This has happened last year as well, so I wouldn't recommend running something important on a .io domain: https://news.ycombinator.com/item?id=12813065

user:	wjkohnen
created:	August 25, 2017
karma:	8