Service linked to hostgroup / notifications

[Neu, Timothy]

As I understand it, running NTP on a VM is a complete waste of
resources, as there is no real per-VM clock to keep in sync. (i.e.,
you're updating ether)  VMWare "fakes" a clock whenever a process tries
to access one.

I know there are some kernel boot parameters that can be added to
improve time accuracy inside a VM.  Not sure if I found them on Redhat's
site or VMWare's...   That and VMWare tools time synchronization is the
best I've been able to come up with.


Tim Neu
Tel +1 651 756 6383
Fax +1 651 490 4310
Mobile +1 651 238 8816
tneu at sjm.com
-----Original Message-----
From: Kevin Keane [mailto:subscription at kkeane.com] 
Sent: Friday, February 27, 2009 3:25 AM
Cc: Nagios-users at lists.sourceforge.net
Subject: Re: [Nagios-users] Service linked to hostgroup / notifications

This isn't really a Nagios issue any more - but here is my experience 
with this issue:

I used to have the same problem with VMWare Server 1.x. Haven't seen it 
happen in version 2.x, so upgrading might be a good idea if there is no 
reason for you not to do it. In 1.x, the problem of clock 
desynchronization really was quite dramatic.

The real problem was that the clock drifts so fast that it exceeds ntp's

threshold for how much it will adjust. IOW, ntp just plain can't keep up

with the extreme clock drift by VMWare. My workaround: create a cron job

that as much as every ten minutes restarted the ntp daemon. On restart, 
ntp will synchronize the time regardless of what the differential is. Of

course, the ten minute interval would sometimes be substantially 
different from actual ten minutes, but that doesn't really matter much 
here. During these ten minutes, the clock may still drift quite a bit, 
but at least it will get corrected fairly quickly.

David Fontaine wrote:
> NTP is configured for every server, except for some virtual machines 
> synchronizing their clocks with the host on which they are running.
>
> It happened once or twice that the clock got desynchronized, even 
> using NTP so I just want to make sure everything is in sync by 
> monitoring the servers with nagios.
>
> On Thu, Feb 26, 2009 at 7:48 PM, Lee Azzarello <lee at dropio.com 
> <mailto:lee at dropio.com>> wrote:
>
>     On Thu, Feb 26, 2009 at 1:17 PM, David Fontaine
>     <dav.fontaine at gmail.com <mailto:dav.fontaine at gmail.com>> wrote:
>     > Hello,
>     >
>     > I am monitoring a few dozen of servers and I'm really satisfied
>     with nagios.
>     > This is a great tool.
>     >
>     > However, there's one (actually more than one) thing that I can't
>     figure out
>     > :
>     >
>     > I define a service :
>     >
>     > define service{
>     >         use                     generic-service
>     >         hostgroup_name          linux-servers
>     >         service_description     Time
>     >         check_command           check_time!public
>     >         }
>     >
>     > This service applies to a host group so that I don't have to
>     define the
>     > service for each server. The command doesn't matter but for
>     completeness
>     > here's what it does : it compares the time on a remote server
>     (snmp) to the
>     > local time and report the difference.
>
>     Going out on a limb here...have you considered using the Network
Time
>     Protocol to keep all your host's clocks in sync with an Internet
scale
>     network of federated time servers available to you for free?
>
>     I'm using NTP on a network of 40 hosts and I never have worried
about
>     their clocks getting out of sync.
>
>     -lee
>

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-OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise
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