Dynamic DNS server

This software provides a cheap dynamic DNS solution for anyone with a Linux VPS (or a friend who is willing to share one).

I occasionally want to access my home PC while I’m away from home, but my ISP doesn’t offer static IP addressing.  Thanks to a resurgence in the popularity of virtualisation, servers are extremely cheap to rent nowadays (as little as £3/month).  In addition to the server hosting this website (and others), I run a DNS nameserver (using PowerDNS) on one of my other virtual servers.  With this simple BASH script and a web interface, my server gained dynamic DNS capabilities and allows me to access my home PC despite the varying IP address.

The packaged script and web interface run on the nameserver, and a separate script is run on the target machine (in my case, the home PC), which curl’s the web interface periodically to update the necessary A-record.  It is important for the A-record to have a small TTL value (e.g. 60 seconds), in order to allow updates to propagate through DNS caches at a reasonable speed.  Look at the code for the PHP web interface to understand the syntax for the CURL request.

Rather than leave the home PC on 24/7 and waste electricity, I also created a remote interface to dispatch wake-on-lan packets.

Download: Dynamic DNS scripts
Latest version (github): battlesnake/ddns

Camera habbits

I wanted to have a brief forage into three dimensional data visualisation.  The photos on this website provided me with a quick way to build a dataset: digital cameras store plenty of metadata in each photo, in addition to the image itself.

I put together a little PHP script that reads the “camera settings” data from every photo on this site and collates it into a flat database.  An R script then takes two columns from the database and produces 2D density plots, (no longer) shown below.  An initial attempt to produce full 3D animations using R was hampered by a resource leak in the RGL graphics package.  This was resolved by having the R script render only one frame rather than the whole animation.  A separate BASH script calls the R script repeatedly to render each frame of the animation, and then to coalesce the frames.

This visualisation allowed me to see what camera configurations I tend to use the most, information which has no real value to me besides curiosity at the moment.  It has also persuaded me to move away from using R for analysis, it is such a painful environment for doing anything remotely graphical…

3d-FocalLength-Aperture-ShutterSpeed-high

The faster shutter speeds are enabled by the reasonable sharpness offered by my 35mm prime at its open end, while the blob around f/4 to f/5 is due to the widest ends of my Sigma 150-500mm, Sigma 10-20mm and (now sold) Nikon 55-300mm.  The blobs centered at 3″/f10 are probably from waterfall long-exposures, jupiter and the slower shutter speeds around the f/1.8 aperture region will be from fibre-optic art.  The cluster from f5/150mm-f6.3/500mm is from using the big Sigma wide open, with the cluster around 500mm being mostly from low-budget astrophotography with the same lens.  It’s interesting how easily trends can be visualised with just a little bit of crude scripting.

The end result of all this is that I abuse the open end of my f/1.8 prime far too much, when I could probably get sharper, less hazy photos by resorting to a slightly slower shutter instead…