Monitoring Apple Time Capsule with Nagios
Backups of desktop systems should be a standard feature for all IT environments. For users of OS X on Apple Systems, this requirement is addressed through Time Machine, a built-in backup system that runs transparently in the background. For home users and small businesses (or even larger businesses with few Apple Desktops), Apple offers an archiving system (which also doubles as a wireless access point when needed) called Time Capsule
Nagios organizes monitoring in to two categories: host and services. Host availability is monitored by configuring a host object. For the services to the monitored on the host, a service object is created for those services of interest. Generally, the host object once installed and activated will using ping to determine the availability of the host. Service objects will generally use a plug-in, sometimes a custom plug-in, to determine the availability of services on that host. For the purposes of this posting, I am using a widely available plug-in called check_ifstatus which can be installed a part of the FreeBSD ports nagios-plugins package. If installed from the FreeBSD ports collection, the plug-in will automatically be configured for use by Nagios and can be used in a service object or template directly.
When adding a new device type to Nagios, it’s important to consider how that device will be represented on Nagios’ web pages. This means selecting an appropriate icon, vrml image and statusmap image to represent the device. The FreeBSD ports collection comes with a set of logos that cover most common devices called nagios-base-logos. For the Time Capsule, I want to use an icon that looked like the device. I found a satisfactory one at deviantArt by ElevatorHappyFun. Nagios uses logos that are 40×40 pixels, so I use Photoshop to resize the icon of the Time Capsule to that size (this is in the Image menu in Photoshop) and then (based on guidance from the Nagios Wiki ) I change the image mode to Indexed from RGB format (also in the Image menu). Because the Time Capsule is a long short box, there is a lot of blank space above the box. That’s ok. The image needs to be square to work properly with Nagios. This work is now saved as a PNG file (I call it time-capsule40.png), transferred to the Nagios server and installed in the Nagios image file location (which on FreeBSD is /usr/local/www/nagios/images/logos by default). The final step is to create another version of the icon in GD2 format. When the gd FreeBSD port is installed (as part of installing Nagios), pngtogd2 is also installed. I do the conversion by entering the command line pngtogd2 time-capsule40.png time-capsule.gd2 0 1 to create an uncompressed GD2 formatted icon file (The Nagios FAQ suggests it be uncompressed).
To add the host to Nagios, I create a template for Time Capsule devices (I have three in my network) and then create a host object for each Time Capsule referencing that template. Here is the template entry:
define host{
name apple-time-capsule
icon_image time-capsule40.png
statusmap_image time-capsule.gd2
vrml_image time-capsule40.png
use generic-switch
register 0
}
Because I am using Nagios 3.2.1, I can take advantage of a new feature in Nagios 3 by putting the information on the images directly in the host template. The old approach of using a hostextinfo object still works as well, but is deprecated in Nagios 3 and will likely no longer work when Nagios 4 comes out.
With the host template in place, I now add the three Time Capsules in my network using these objects:
define host{
use apple-time-capsule
host_name red-tc
alias Red Time Campsule
address 192.0.2.2
hostgroups wireless-ap
parents blue-tc
}
define host{
use apple-time-capsule
host_name blue-tc
alias Blue Time Campsule
address 192.0.2.3
hostgroups wireless-ap
parents switch
}
define host{
use apple-time-capsule
host_name green-tc
alias Green Time Campsule
address 192.0.2.4
hostgroups wireless-ap
parents blue-tc
}
Besides host availability, I want to know that all the interfaces in the Time Capsule are operational. To do that, I am using the check_ifstatus plug-in. Here is the service object to activate this checking:
define service {
service_description Network Interface Status
check_command check_ifstatus!public
use network-service
host_name red-tc,green-tc,blue-tc
}
Now, with a restart of Nagios, these three Time Capsules will be checked for availability with ping and have the status of the interfaces checked using check_ifstatus using SNMP version 1 and a community of public.
Logging data for service testing results (when everything is working properly) should look like this:
[05-11-2010 00:00:00] CURRENT SERVICE STATE: red-tc;Network Interface Status;OK;HARD;1;OK: host '192.0.2.2', interfaces up: 6, down: 0, dormant: 0, excluded: 0, unused: 0
[05-11-2010 00:00:00] CURRENT SERVICE STATE: green-tc;Network Interface Status;OK;HARD;1;OK: host '192.0.2.4', interfaces up: 6, down: 0, dormant: 0, excluded: 0, unused: 0
[05-11-2010 00:00:00] CURRENT SERVICE STATE: blue-tc;Network Interface Status;OK;HARD;1;OK: host '192.0.2.3', interfaces up: 7, down: 0, dormant: 0, excluded: 0, unused: 0
blue-tc shows 7 interfaces because its wan interface is in use. This port is not used on the other two since they are being used to extend an existing wireless network. Two other configuration notes:
- The Time Capsules are configured with static IP addresses. While not strictly required, I don’t want to have to depend on DNS resolution in order to monitor devices on my network, so I choose to statically configure devices that are not portable.
- The Time Capsules are configured to respond to SNMP queries (version 1 or 2c only) using the community public.
Now, I am able to see the Time Capsules in my status map as well as get notices from Nagios should any interface go down any of the Time Capsules become unavailable.
