I would be very very wary of running Nagios on a VM (we use VMware here). The
reason for this is Clock Skew.
Clock Skew causes the virtual clock on the guest OS to lag behind then skip
forward depending on the loading and sleep times of the guest. Note that this
will not affect 'Para-virtualised' guests as they share the hardware clock, but
these are only possible in some Xen guests at the moment AFAIK and are not
common. VMWare can't do them.
On a lightly loaded physical machine your clock skew will be negligible but as
load goes up you can get the guest clock lagging as much as 10sec or even more.
This can screw up latencies, scheduling, rate calculations (such as CPU use
and net use) and so on. In addition any monitoring of virtualised resource
(CPU, Memory) will be completely wrong unless you obtain the values from a
source which is aware of the virtualiasation (eg VMWare tools API or
VirtualCentre API for vmware)
Clock skew and virtualised resource monitoring has caused too many problems in
our tests and we now only use physical servers for Nagios (and MRTG).
I have a Nagios plugin check_vmware at
www.steveshipway.org/forum<http://www.steveshipway.org/forum> for monitoring
VMware virtualised resources via the API to get meaningful values - previous
used check_esx3 but this has been superceeded by the use of the VC API in
check_vmware
Steve
________________________________
From: Juki [juki.e...@gmail.com]
Sent: Friday, 13 November 2009 12:42 a.m.
To: Nagios Users Mail-list
Subject: [Nagios-users] Installing Nagios Server on a Virtual Machine
Hello people,
I would like to know if it is advisable (or best practice) to install and run a
Nagios monitoring server on a virtual machine (in this case, with OpenSuSE as
the OS) with
the intention of monitoring physical hardware client machines on the same LAN.
If so, what known issues should I look out for in this case?
Thanks,
Juki
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