The sys admin's daily grind: iWatch
In a Minute
Recently, sys admin Charly was faced with the task of synchronizing a directory on a server with two NFS-mounted clients. He wanted the whole thing to happen quickly and to be easily manageable, which ruled out DRBD and GlusterFS.
My sync setup looks roughly like this: An application server cyclically reads values from a database, generates HTML files and some images, and dumps everything in the /source directory. I use NFS 4 to mount the /dest1 and /dest2 directories. When any new data arrives in /source, I want it to reach the two target directories /dest1 and /dest2.
Simple and Been Here for Years
Because complex solutions are out of the question, actually the only option left is to dump the task on inotify subsystem's plate. Inotify has been part of the kernel since 2.6.13 and provides an interface to filesystem events for userspace programs.
Apart from incron [1], I've hardly found a use for it so far, but it should be ideal for quick syncing of directories – or at least, these were my ideas on the matter. What was missing was the right tool for the task. Some quick research brought to light two candidates: lsyncd [2] and iWatch [3], but I'll focus on iWatch here.
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