dns – Made by Mikal

Amazon Linux 2023, DNS, and systemd-resolved — a story of no caching

Post author:mikal
Post published:November 11, 2024
Post category:AmazonLinux AWS

I’ve learned a few things on an adventure this week, and I figure I should probably write them down.

First off, AWS throttles the number of DNS queries you can perform on a VPC. Apparently you’re limited to 1,024 packets for Elastic Network Interface (ENI). I am a little unclear on if the limit is per instance ENI, or the ENI on the VPC that is the DNS server. I am also unsure if that’s 1,024 request packets, or 1,024 total packets, but either way there is definitely a limit after which you will be throttled.

Secondly, AL2023 disables the systemd-resolved DNS caching behaviour, which means its pretty easy to hit that throttling limit. When you google for solutions you’ll find re:Post posts recommending dnsmasq, which is a perfectly fine piece of software but not really necessary if you already have systemd-resolved installed on your instance (as you do with AL2023). (more…)

Python DNS modules

Post author:mikal
Post published:December 31, 2005
Post category:Python

My first python script involves doing some DNS lookups (for TXT records if that matters), and I am currently working through using the pydns module for this. Is this really the best DNS module to use for python though? For a start, it was last released in May 2002, and the documentation is somewhat sparse...

What’s happening with frozenchicken.com?

Post author:mikal
Post published:November 4, 2005
Post category:Google

Gordon at work asks me what is happening with www.frozenchicken.com. If you hit the site, then you get the Google search interface. This is because of the DNS configuration for the domain: challenger:~# host www.frozenchicken.com www.frozenchicken.com is an alias for www.google.com. www.google.com is an alias for www.l.google.com. www.l.google.com has address 66.102.7.147 www.l.google.com has address 66.102.7.99 www.l.google.com has address 66.102.7.104 www.frozenchicken.com is an alias for www.google.com. www.google.com is an alias for www.l.google.com. www.frozenchicken.com is an alias for www.google.com. www.google.com is an alias for www.l.google.com. You can see that www.frozenchicken.com is an alias for www.google.com, which in turn points to what is presumably my local cluster. So why do all the links of the Google page then point via www.frozenchicken.com? Well, because they're relative URLs, they use the hostname from the browser.