I'm getting ready to implement a new Nagios monitoring system at our soon-to-be-production server, and I'm using Nagios v3 this time. Because I sort of figured out the configuration on my own last time, and it grew in a very organic (read: unplanned) way, the config is a mess. That is going to be different this time, thanks to Nagios 3 Enterprise Monitoring. It's not an intro guide to Nagios, that's for sure. The first chapter deals with what's new. The 2nd chapter deals with streamlining the configuration for large installations. It's been very educational in teaching me how various hostgroups and service groups can work together to really make life easier for configuring monitoring.
After reading this book pretty much cover to cover, I decided that I needed to logically map out the various relationships of my services, to figure out the inheritance policies (Nagios supports multiple inheritance in configuration objects).
I started looking for a good free diagramming tool, first on Windows then on Linux. Windows was hopeless. I found lots that looked promising, but ended up being shareware. I don't have MS Office Pro on my personal laptop, so I didn't have Visio handy, and I wasn't going to buy a piece of software when I was sure that something good and free existed.
Giving up, I booted into Linux to see if anything I didn't know about was in synaptic. Of course not. The best diagramming solution in Linux is Dia, and I'm sorry to say it, but it's ugly. Really ugly. I'll use it if that's the only thing available and I'm just looking for something quick, but I won't like it.
I kept looking, and finally out of desperation I did a search for online applications, and I hit the jackpot. I found Gliffy. It's a flash diagramming application with built in stencils for all sorts of things, and the ability to add your own clipart. It'll even export to Visio.
I was impressed. It's free for personal use up to 5 public diagrams. You can pay $5/month for unlimited drawings and removing the ads, and there are corporate versions that have built in collaboration. It's easy to use, and it helped me a lot. Here's a drawing of some of my nagios groups:
If you're in the market for a cross-platform diagramming solution, you could do a lot worse than Gliffy.