Local DNS Resolution Mystery ... RESOLVED !!

Yo,

I know it’s been a long time since I rapped at ya. But I’m finally getting around to upgrading my ancient weak-sauce blog, And it’s got my mind all up in that long-form writing headspace, you catch my drift? And today I absolutely threw down on a simple fix for an issue that’d been stuck in my craw for about a year now.

So, here I am, droppin’ some keywords on ya and dumpin’ a log to hopefully, you know, offer some support to some other future frustrated dude as the DNS Gods harsh all over his mellow.

TL;DR

it was an IPv6 thing.

The Problem

It should come as no surprise that I need me some consistent /etc/hosts resolution coming back from:

Google Chrome
Firefox
curl
Node.js’s dns module

Chrome had never been an issue; it was bonafide. I could get around issues in curl using –resolve, but that’s a pain in the ass. The real troublemakers were Firefox and dns, the latter introducing a problem into webpack-dev-server. At least with Firefox I could do DNS Spoofing with Charles – until I needed to proxy WebSockets – but anything at the shell-level was a total no-go, bro.

My Situation

I had an entry 192.168.99.100 vbox.redacted.com – yep, redacted.com – in my /etc/hosts. Now, sometimes the name would resolve locally. And then suddenly, it wouldn’t … instead it’d resolve to an external IP. For a long periods of time. Firefox would seize up, curl would start doing it’s pain-in-the-ass dance … I mean, it was a bad scene. We’re talking beyond dogs-and-cats-living-together territory. Meanwhile, dig vbox.redacted.com would mock me by resolving properly. Every. Single. Time.

I mean, I figure mr. Foley’s gotta lay all this low-down on ya, just to clue you into how draggingly low-down it had gotten. In all desperation, I’d even gone so far as to set up dnsmasq and hack my /etc/resolv.conf with ‘nameserver 127.0.0.1’ to try and get OS X to behave. But no dice. Turns out that the hostname resolved to an external IP because our ‘*.redacted.com’ wildcard entry got applied once the query got Forwarded upstream. So, yeah - hooray for us.

And the ‘long periods of time’ thing, that was clearly a DNS caching issue … Yet one that no amount of mdnsflushcache‘ing would resolve. I could sometimes get things to work by leaving this dreadful hack running in a shell:

watch -n 1 dig local.redacted.com

… but, that was a darker time.

Today Was Different

Because today I finally watched the dnsmasq logs while I did dns.lookup-style resolution from the shell with the help of atorstling/getaddrinfo. And I saw this:

dnsmasq[47]: query[A] vbox.redacted.com from 127.0.0.1
dnsmasq[47]: /etc/hosts vbox.redacted.com is 192.168.99.100
dnsmasq[47]: query[AAAA] vbox.redacted.com from 127.0.0.1
dnsmasq[47]: forwarded vbox.redacted.com to 8.8.8.8
dnsmasq[47]: reply vbox.redacted.com is <CNAME>
dnsmasq[47]: reply sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com is NODATA-IPv6
dnsmasq[47]: query[A] sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com from 127.0.0.1
dnsmasq[47]: forwarded sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com to 8.8.8.8
dnsmasq[47]: query[AAAA] sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com from 127.0.0.1
dnsmasq[47]: forwarded sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com to 8.8.8.8
dnsmasq[47]: reply sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com is 52.55.84.99
dnsmasq[47]: reply sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com is 54.84.80.102
dnsmasq[47]: reply sw33tj35u5.0MF6.us-east-1.elasticbeanstalk.com is NODATA-IPv6

“Hey, what’s this AAAA shit?” I asked myself. The Community patted me on the back and told me, “that’s IPv6”. So, might it be that my /etc/hosts was only providing a trustworthy IPv4 mapping?

OMG, do you mean … I just have to …

Yes, You Just Have To

… fully round out the /etc/hosts entries

# provide both IPv4 and IPv6 mappings
127.0.0.1          local.redacted.com
::1                local.redacted.com
192.168.99.100     vbox.redacted.com
::ffff:c0a8:6364   vbox.redacted.com

A quick kill -HUP to dnsmasq, and … everything is suddenly right as rain. Firefox resolves like Chrome. My webpack bundle built on the backs of ten thousand JavaScript tortises suddenly proxies reliably.

Yes, today was truly different

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