DNSMASQ to the rescue⌗

This post will endeavour to describe a problem I encountered at work a while ago, and ended up fixing by deploying dnsmasq.

The problem⌗

One of the legacy pieces of code I used to look after was a monolithic java application, deployed onto a web application server platform. In order for end users to engage its functionality, their accounts had to be authenticated with the company’s central identity and access management solution - which in this case was Windows Active Directory. The application used a library called JCIFS to integrate with the Windows AD infrastructure, but unfortunately this integration was rather näive, in that it used a DNS A record to discover which AD servers to connect to. If you’ve worked with AD at all, you probably already know that it uses a plethora of DNS SRV records in addition to basic A records, but at the time this application was originally written, JCIFS didn’t appear to support using SRV records to determine the right domain controllers to connect to.

AD and SRV records⌗

If you aren’t familiar with AD and SRV records, then perhaps a short explanation is in order. Most people are somewhat familiar with a DNS A record, even if they don’t know that’s what it’s actually called. It’s nearly always the address they type in the address bar of their web browser (although sometimes it might be a CNAME - but let’s not digress too far). In simple terms an A record is a mapping of a human readable address like “www.google.com” to an actual IP address.

SRV records