The webcam image at webcam.idefix.net
is getting popular at the moment due to the use by nedWeer.nl
peaking at 0.5 requests/second.
Since the image is imported from a different server in a proxying setup this
was causing quite some traffic on my adsl line. The image doesn't update every
second, so I had a look into caching possibilities with apache 2.2. I wanted
to use the memory cache for just this one object but I started with the disk
cache because it's easier to debug and see the files on disk.
work, and I could not figure out why. I followed the instructions found in
apache2 - Apache Reverse Caching Proxy - why isn't it caching? - stackoverflow.com
but still no caching happening.
I set up a separate virtual server with the logging set to level 'debug'
and found the following interesting line in the log:
[Thu Feb 06 16:24:59 2014] [debug] mod_cache.c(370): (12)Cannot allocate memory: cache: Cache provider's store_body failed!
This looked more like a memory cache problem than a disk cache problem. But
the memory cache wasn't configured at all. I decided to remove the memory
cache support completely and that fixed things with the disk cache. The
debug log suddenly had the right messages:
[Thu Feb 06 16:25:59 2014] [debug] mod_cache.c(633): cache: Caching url: /camwindow.jpg
Now the webcam image is cached for 120 seconds. Which saves some traffic on
the ADSL line.
Requests still going at about 0.5 requests/second at busier times. The proxy
reduces the impact on ADSL traffic and ping delays.