How to test the uptime of a webserver?

[Matthew Seaman]

Redd Vinylene wrote:
> On Sun, Aug 31, 2008 at 2:22 AM, Moises Castellanos <m2o7i1 at gmail.com> wrote:
>>
>> On Sun, Aug 31, 2008 at 7:05 PM, Redd Vinylene <reddvinylene at gmail.com>
>> wrote:

>>> I got this dedicated server which is exposed to DDoS attacks quite
>>> frequently. Say I need to host a website on it, is there any way of
>>> telling how often it is actually online (to the rest of the world)?
>>>
>>> Maybe make some sort of ping script from a remote server?

>>     You can install nagios and monitor the web server. It will send you an
>> email when
>> the server is down and when is up again. With this information you can know
>> the uptime
>> of the web server.

> I'd have to install Nagios on a different server then, right? I doubt
> the actual server knows when its ISP's link drops (or just slows down)
> due to an attack.

Not necessarily.  You can install nagios on your web server and use it
to monitor a server at the other end of your wan link -- usually a
machine in your ISPs infrastructure[*] -- on the basis that if you can get 
packets out, then other people can get packets in.  The trick is to monitor 
something that isn't too far away, or you'll end up monitoring the 
availability of other people's networks, rather than your own.

There's a lot more can be done than just monitoring connectivity by
sending ICMP ping packets every so often.  There are any number of
ways a web server can go wrong -- processes can crash, critical disk partitions can fill up, load spikes can overwhelm the machine's capacity.
You can develop a range of different nagios tests that should tell you
pretty much at a glance just what has gone wrong.  Takes all the fun out
of diagnosing the problems perhaps, but it does mean you'll be back to
bed sooner when the pager goes off in the small hours.

	Cheers,

	Matthew

[*] Some ISPs provide machines specifically for this purpose.

-- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW

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