#serverdensity

I recently stumbled upon the site Server Density while upgrading all my servers and signed up for the service. It as a great pretty interface, a customizable dashboard, and pretty extensive alert capabilities. They also have a free trial so I suggest signing up. The one thing I did not like was the inability to scan for a specific string on the website to confirm if the website is still operational, like with host-tracker.com.

The good news is Server Density allows you to create python plugins to run at the update interval on any/all of your servers. This gives you free reign over your reports. Using this tutorial, I will explain how to manually create and install this and any other plugin. Or you can just download or install it from the below links.

GitHub - https://github.com/arzynik/sd-webcheck

Server Density Plugin - http://plugins.serverdensity.com/webcheck

Create your plugin

First, log into your SD account and go to Plugins. Then add a new plugin and name it WebCheck.

Add your plugin to your server

Next you will need to ssh into your server and create the directory

mkdir /usr/bin/sd-agent/plugins/

In that directory, create a new file called WebCheck.py. This will be the main and only file for the plugin. Grab the code from https://github.com/arzynik/sd-webcheck/blob/master/WebCheck.py and paste it into the file.

Configure your plugin

If this is your first plugin, you will need to add your plugin directory to your plugin config file. Open up /etc/sd-agent/config.cfg and replace the plugin_directory line with

plugin_directory: /usr/bin/sd-agent/plugins

WebCheck allows you to check the status of as many sites as you want. In order to check they you will need to enter a new config entry for each site, using the below fields:

name - The name and key you want to use on the SD interface. Remember that all "." will be replaced with "_" due to api limitations.

url -

find - The regex or string to search for. I typically just use an html tag but you can search for anything.

result - The result is the regex quantifier. Lets say you want to search from </html>, you would keep this True. Or lets say you want to search for Parse Error, you would then make this False.

Here is an example config entry

[WebCheck 1] name: devin.la url: http://devin.la/ find: </html> result: True

Restart the agent service to load the changes. Once it is restart it will begin sending data to SD

/etc/init.d/sd-agent restart

Settings up alerts

Because WebCheck only returns a boolean result, you probably wont be using it with graphs much. The alerts, however, are extremely useful. I personally recommend the iPhone push notifications, as they are uber fast.

In your Server Density account, go to Alerts and click add new alert.

Select your server that you installed it on, who is going to get it, and the alert type.

For Check, select WebCheck.

For Key, enter the name of your config entry. For me it is devin_la.

For Trigger threshold, set it to Less than 1.

Add it and you now know when your server is messed!

I love it!

Over the past 2 weeks I've been fortunate enough to talk about D3, Rickshaw and Backbone at 5 events in Dundee, Dublin, Basel, Vienna and Hannover. This has been a great experience and I am very gratefull that Server Density values this sort of activity.

Over the last two weeks I've learnt alot:

Knowing a presentations audience is key. Subtle changes in content or audience can have a massive impact on how a talk is recieved

In every major city in Europe there are tech meetups full of smart, open and enthusiastic designers and developers that are crying out for people to share their experiences.

There is huge value in presenting the same topic multiple times to different audiences. It allows you to iterate, respond to feedback and test theories.

Travelling for work is not glamourous, it's tiring and can be lonely. But the conversations with like minded individuals make it worthwhile, as does the opportunity to show a product that you are very proud of to a new audience.

I've learnt that Data Visulisation is a topic that every designer, developer or business person can get alot out of and thoroughly enjoy.

You would be excused for thinking that people who do monitoring software for a living would know how to do a datacenter migration, but then maybe the Boxed Ice guys running Server Density are just amateurs.

https://twitter.com/#!/serverdensity/status/190436930071183360