On Mon, 24 Aug 2015, Page, Jeremy wrote:
I think the problem is looking at it as a binary up/down issue when in fact
you should be able to determine the problem is occurring when the check takes
longer than a specific threshold. A page taking a second or two to load is
going to cause close to the havoc a 404 does.
The problem is when you don't have a site-wide problem, but rather an
intermitten problem, your external test may or may no see it.
If you have 10 systems behind a load balancer, and one of those 10 systems has a
problem, at best your external test is going to get an error 1 out of 10 times
(at worst, your load balancer is going to tend to put your external test to one
server instead of rotating it across all 10, in which case you may never see the
problem)
looking at logs is 100% accurate at detecting logged problems :-)
logs won't detect problems that aren't logged (which is why I think you should
log how long it took to service the request), so you need the external test as
well. But there is a LOT of stuff the extenal test won't detect.
David Lang
As far as false positives go the same is true for the failed attempt. This is
why Nagios and most other monitoring systems offer the ability to confirm a
failed check. Personally I like to check at moderately long intervals but
recheck quickly if I discover a possible failure.
Finally, as Adam pointed out, just because the page returns does not determine
that it's functional. Acceptable user experience is (should) be the thing you
are trying to verify.
________________________________________
From: tech-boun...@lists.lopsa.org [tech-boun...@lists.lopsa.org] on behalf of
Edward Ned Harvey (lopser) [lop...@nedharvey.com]
Sent: Monday, August 24, 2015 6:51 AM
To: Adam Moskowitz; tech@lists.lopsa.org
Subject: Re: [lopsa-tech] Server Overload and Log Processing
From: tech-boun...@lists.lopsa.org [mailto:tech-boun...@lists.lopsa.org]
On Behalf Of Adam Moskowitz
I don't see how that can be true: If "a bunch of users" will get errors,
I believe your page download tester will also see those same errors. If
it's not seeing those errors, what good is it?
If you server can handle 100,000 requests per minute, and you get 101,000 requests a minute, then
1% of your users will get "Page cannot be displayed" or something similar. You have a 99%
chance that your download tester will fail to detect the problem. If it's sustained, you'll
probably detect the problem after 100 minutes, but you really should have detected it sooner, and
if you detect the problem only as "page failed to download" by your download test, then
you don't know why it failed, and the problem doesn't persist, and you'll probably brush it off as
a false alarm.
Yes, you should still be looking at your logs, but I believe that what's
more critical is that you monitor the service *from the user's point of
view*, and that monitoring should reflect the users' experiences as
closely as possible.
Agreed.
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