Apr 252015

So for ages I've been having these mysterious slow downs in connecting to some of my internal servers. A few seconds, but once connected things are working normally.

And of course I kept putting off having a look into the problem, because firstly I'm lazy, secondly there are other more interesting things to look at, and thirdly I'd already discounted the obvious (actually I'd "fixed" it but made certain assumptions). But it's finally time to have a look.

Now I said I'd earlier discounted the obvious but decided to have a look any way. The thing to remember is that when you connect to a server it almost always performs a DNS lookup on your network address, so a mysterious slow down could well indicate that DNS resolution is to blame. You could perform diagnostics to determine what the problem is, but in all the decades I've been solving issues with computers whenever a mysterious slow down has occurred when connecting over the network, then the problem has almost always been the DNS resolver.

Taking a look at /etc/resolv.conf on the relevant server (a Linux container), and I find the file has a nameserver within it that was retired several weeks ago! Fixing that solved the issue.

Lessons learnt :-

  1. Just because you have a centrally distributed /etc/resolv.conf that is automatically installed on all your home network doesn't mean to say that it is always automatically installed. My Linux containers don't get that centrally distributed file (which had been corrected!).
  2. Don't assume that it's not the obvious even if you have reasons for thinking it couldn't possibly be the obvious (see #1).