Re: recommendations for external montioring services?

[Robert Brockway <robert () timetraveller org>]

On Mon, 12 Dec 2011, Eric J Esslinger wrote:

> I'm not looking to monitor a massive infrastructure: 3 web sites, 2 mail 
> servers (pop,imap,submission port, https webmail), 4 dns servers 
> (including lookups to ensure they're not listening but not talking), and 
> one inbound mx. A few network points to ping to ensure connectivity 
> throughout my system. Scheduled notification windows (for example, 
> during work hours I don't want my phone pinged unless it's everything 
> going offline. Off hours I do. Secondary notifications if problem 
> persists to other users, or in the event of many triggers. That sort of 
> thing). Sensitivity settings (If web server 1 shows down for 5 min, 
> that's not a big deal. Another one if it doesn't respond to repeated 
> queries within 1 minute is a big deal) A Weekly summary of issues would 
> be nice. (especially the 'well it was down for a short bit but we didn't 
> notify as per settings') I don't have a lot of money to throw at this. I

Hi Eric.  The feature set you are describing should be in any monitoring 
system worthy of the name.  I've used Nagios to good effect for the best 
part of the last 12 years or so.  Before that I used Big Brother, which 
sucked in various ways.

I did an evaluation on a wide variety of FOSS monitoring systems 2-3 years 
ago and Nagios won at the time (again).  Generally I found the 
alternatives had problems that I considered to be quite serious (such as 
being overly complicated or doing checks so frequently that they loaded 
the systems they were supposed to be monitoring[1]).

I'm currently trialing Icinga, a fork of Nagios.

Puppet can be set up to manage Nagios/Icinga config which cuts down on the 
admin overhead.

Nagios/Icinga can be hooked up to Collectd to provide performance data as 
well as alert monitoring.

One concern about external monitoring services is the level of visibility 
they need to have in to your network to adequately monitor them.

My recommendation is to do a proper risk assessment on the available 
options.

> DO have detailed internal monitoring of our systems but sometimes that 
> is not entirely useful, due to the fact that there are a few 'single 
> points of failure' within our network/notification system, not to 
> mention if the monitor itself goes offline it's not exactly going to be 
> able to tell me about it. (and that happened once, right before the mail 
> server decided to stop receiving mail).

There are a couple of ways to deal with this.  Some monitoring 
applications can fail-over to a standby server if the primary fails.  But 
this isn't even really necessary.  You will arguably gain higher 
reliability by running multiple _independent_ monitors and have them 
monitor each other[2].  I have often used this approach.

The principal aim here is to guarantee that you are alerted to any single 
failure (a production service, system or a monitor).  Multiple 
simultaneous failures could still produce a blackspot.  It is possible to 
design a system that will discover multiple simultaneous failures, but it 
takes more effort and resources.


[1] Sometimes I wonder if the people developing certain systems have any 
operational experience at all.

[2] A system designed to fail-over on certain conditions may fail to 
fail-over, ah, so to speak.

Cheers,

Rob

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