It's a few years old, but Facebook has talked a little bit about their
DNS infrastructure before. Here's a little clip that talks about
Cartographer: https://youtu.be/bxhYNfFeVF4?t=2073
From their outage report, it sounds like their authoritative DNS
servers withdraw their anycast announcements when they're unhealthy.
The health check from those servers must have relied on something
upstream. Maybe they couldn't talk to Cartographer for a few minutes so
they thought they might be isolated from the rest of the network and
they decided to withdraw their routes instead of serving stale data.
Makes sense when a single node does it, not so much when the entire
fleet thinks that they're out on their own.
A performance issue in Cartographer (or whatever manages this fleet
these days) could have been the ticking time bomb that set the whole
thing in motion.
On 10/5/21 3:39 PM, Michael Thomas wrote:
This bit posted by Randy might get lost in the other thread, but it
appears that their DNS withdraws BGP routes for prefixes that they
can't reach or are flaky it seems. Apparently that goes for the
prefixes that the name servers are on too. This caused internal
outages too as it seems they use their front facing DNS just like
everybody else.
Sounds like they might consider having at least one split horizon
server internally. Lots of fodder here.
Mike
On 10/5/21 11:11 AM, Randy Monroe wrote:
Updated:
https://engineering.fb.com/2021/10/05/networking-traffic/outage-details/
On Tue, Oct 5, 2021 at 1:26 PM Michael Thomas <m...@mtcc.com
<mailto:m...@mtcc.com>> wrote:
On 10/5/21 12:17 AM, Carsten Bormann wrote:
> On 5. Oct 2021, at 07:42, William Herrin <b...@herrin.us
<mailto:b...@herrin.us>> wrote:
>> On Mon, Oct 4, 2021 at 6:15 PM Michael Thomas <m...@mtcc.com
<mailto:m...@mtcc.com>> wrote:
>>> They have a monkey patch subsystem. Lol.
>> Yes, actually, they do. They use Chef extensively to configure
>> operating systems. Chef is written in Ruby. Ruby has something
called
>> Monkey Patches.
> While Ruby indeed has a chain-saw (read: powerful, dangerous,
still the tool of choice in certain cases) in its toolkit that is
generally called “monkey-patching”, I think Michael was actually
thinking about the “chaos monkey”,
> https://en.wikipedia.org/wiki/Chaos_engineering#Chaos_Monkey
> https://netflix.github.io/chaosmonkey/
No, chaos monkey is a purposeful thing to induce corner case
errors so
they can be fixed. The earlier outage involved a config sanitizer
that
screwed up and then pushed it out. I can't get my head around why
anybody thought that was a good idea vs rejecting it and making
somebody
fix the config.
Mike
--
Randy Monroe
Network Engineering
Uber <https://uber.com/>
