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<P><FONT SIZE=2>Since latency appears to be a problem,<BR>
Are all devices configured to use NTP?<BR>
I had an apche server in the dame boat last week, was drifting often, then would be corrected on next round of ntp syncs. Whoops, 'dame' should be "same"<BR>
In the above sentence.<BR>
Adjusting the sync time to be more frequent, and replacing the MBs CMOS battery did the trick.<BR>
<BR>
I also ended up discovering a new enchanement to the server that was topping out resources, and made it slow to respond to requests.<BR>
<BR>
Your mileage may very.<BR>
<BR>
Best,<BR>
<BR>
<BR>
Paul Krash, system administrator, Exegy, Inc.; 314-218-3602 x 666<BR>
<BR>
----- Original Message -----<BR>
From: Alan Sparks <asparks@doublesparks.net><BR>
To: hobbit@hswn.dk <hobbit@hswn.dk><BR>
Sent: Sun Jun 15 23:42:46 2008<BR>
Subject: Re: [hobbit] Debugging help: bbtest-net gets http test timing wrong<BR>
<BR>
On the Apache servers, they are configured with HostNameLookups Off. My<BR>
own measurements using "conventional" tools (like a loop of curls and<BR>
wgets) consistently show responses <0.2s. The Hobbit problem is that a)<BR>
the problem randomly affects the servers in the list (I have about 64<BR>
servers in the test server), and b) no server that Hobbit suddenly<BR>
reports as "slow" ever appears to be slow from other external tests.<BR>
<BR>
Configurations are matched as close as possibly, accounting for module<BR>
and other differences between Apache 2.0 and 2.2. I'm very sure DNS<BR>
lookups on the Web server end cannot account for this, as it /should/<BR>
show in logs, and affect non-Hobbit probes as well.<BR>
<BR>
It appears that Hobbit implements HTTP testing itself, in the bbtest-net<BR>
codebase. No external tools are used. Yes, resolver and NSS configs<BR>
are the same. And the HTTP tests are specifically targeted at IP<BR>
addresses, not host names, so there /should/ not be a DNS lookup<BR>
involved in the test connection, as far as I can tell from the code...<BR>
<BR>
And yeah, the tcpdump on both ends is planned for Monday. I want to<BR>
somehow prove the response is actually showing up sooner than the test<BR>
says...<BR>
-Alan<BR>
<BR>
Tim McCloskey wrote:<BR>
> I'll take a stab at this but you may have already looked at the things<BR>
> I wonder about or they may not help in any way. I've only thought<BR>
> about this for a couple of minutes so I could be way off.<BR>
><BR>
> You have stated there are a couple servers that seem to respond<BR>
> differently. Can you, 100% consistently, recreate the proper|improper<BR>
> response from the web boxes? If so, look at the changelog between<BR>
> apache 2.2 and 2.0 (assuming that those servers - 2.0, 2.2 - are on<BR>
> the same network and that all of the media setting match ie. 100Fdx<BR>
> 100Fdx, etc.).<BR>
><BR>
> Are you _sure_ you are not using DNS in some fashion, perhaps reverse<BR>
> lookups or perhaps the newer apache config file contains some lookup<BR>
> setting. (can you get away with using the same httpd.conf on the 2.0<BR>
> and 2.2 boxes?)<BR>
><BR>
> What does the network traffic and connections look like on each of the<BR>
> servers? Have you tried running tcpdump on one of the web boxes to<BR>
> see if there are any clues there?<BR>
><BR>
> I don't recall if hobbit uses wget for his http gets. Are all the<BR>
> servers using the same settings in resolv.conf and nsswitch.conf?<BR>
><BR>
> There are probably other things to check but start with making sure<BR>
> DNS is not involved, even if you think it is not.<BR>
><BR>
><BR>
><BR>
> Alan Sparks wrote:<BR>
>> Continuing to try to debug this problem, have tried about everything<BR>
>> I can to resolve the issues with http probes. Including:<BR>
>> * Complete rebuild of the server with CentOS 4.6 and recompile of<BR>
>> Hobbit. Same issues.<BR>
>> * Removing everything from /etc/sysctl.conf, rebooting. Same issues.<BR>
>> * Manipulating the httpd.conf configs on remote servers, forcing<BR>
>> HTTP/1.0, removing ETags, creating a very simple index page to test<BR>
>> against. Same issues.<BR>
>> * Upgrading Apache on sample remote server to Apache 2.2.8 (most are<BR>
>> 2.2.4). Same issue.<BR>
>> * Recompiling Hobbit with debugging flags, to make sure the optimizer<BR>
>> is not applied. Same issue.<BR>
>><BR>
>> The only two servers I have that seem to work consistently well are a<BR>
>> pair of Apache 2.0.52 servers. The 2.2.4+ servers all seem to give<BR>
>> Hobbit issues. Although, again, repeated curl or wget probe cycles<BR>
>> against the servers from the Hobbit server never show more than a<BR>
>> 0.2s response time.<BR>
>><BR>
>> But, Hobbit continues to report things like:<BR>
>><BR>
>> <A HREF="http://10.1.17.251/">http://10.1.17.251/</A> - OK<BR>
>><BR>
>> HTTP/1.1 200 OK<BR>
>> Date: Mon, 16 Jun 2008 00:54:03 GMT<BR>
>> Server: Apache/2.2.8 (EL)<BR>
>> Last-Modified: Sun, 15 Jun 2008 00:37:00 GMT<BR>
>> ETag: "7c809f-9b-44fa9b5806300"<BR>
>> Accept-Ranges: bytes<BR>
>> Content-Length: 155<BR>
>> Connection: close<BR>
>> Content-Type: text/html; charset=UTF-8<BR>
>><BR>
>><BR>
>> I can't come up with anything other than Hobbit as a cause. But is<BR>
>> there anything I can do to trace what is happening internally to get<BR>
>> past this problem? Any ideas at all would really be appreciated. <BR>
>> Thanks in advance.<BR>
>> -Alan<BR>
>><BR>
>> Seconds: 3.00<BR>
>><BR>
>><BR>
>> Alan Sparks wrote:<BR>
>>> Have a new install of Hobbit (4.2, tried 4.3 snap as well) on a<BR>
>>> fresh install of CentOS 4.6 x86_64, up to date on patches. I have a<BR>
>>> problem with HTTP tests on "random" web servers that I just can't<BR>
>>> figure out.<BR>
>>><BR>
>>> I have about 64 of my hosts in the bb-hosts on this server, and have<BR>
>>> http tests defined for these servers. On most of these servers,<BR>
>>> Hobbit is reporting the "Seconds:" for the response at 3 seconds. <BR>
>>> It seems that it is inconsistent -- one cycle to the next, the<BR>
>>> 3-second response may move to a different set of servers.<BR>
>>><BR>
>>> The http: tests are defined using the IP address of the server - no<BR>
>>> server name (so no DNS lookup).<BR>
>>><BR>
>>> I've run a loop of tests on the same URL using wget and with curl,<BR>
>>> and used my browser and Telnet to connect to the same URL. I<BR>
>>> consistently get a response time of about 0.2 seconds maximum from<BR>
>>> the servers.<BR>
>>><BR>
>>> The bbnet entry in hobbitlaunch.cfg looks like:<BR>
>>> CMD bbtest-net --report --ping --checkresponse --debug<BR>
>>><BR>
>>> With the debugging turned on, I see the following entries<BR>
>>> periodically in the network test log:<BR>
>>> Address=10.1.5.17:80, open=1, res=0, err=0, connecttime=0.002965,<BR>
>>> totaltime=3.006810,<BR>
>>> Address=10.1.5.18:80, open=1, res=0, err=0, connecttime=0.002956,<BR>
>>> totaltime=3.007413,<BR>
>>> Address=10.1.24.67:80, open=1, res=0, err=0, connecttime=0.002860,<BR>
>>> totaltime=3.007120,<BR>
>>><BR>
>>> The problem does not affect the same hosts each time. The problem<BR>
>>> will show a different number of hosts usually each cycle, sometimes<BR>
>>> on same servers, but often on different ones.<BR>
>>><BR>
>>> I've tried the following to see if anything will help:<BR>
>>> * Reducing the number of hosts. If I only have a couple or three in<BR>
>>> the bb-hosts, the problem doesn't manifest.<BR>
>>> * Recompiling. Doesn't help.<BR>
>>> * Changing the test URL. Doesn't help.<BR>
>>> * Adding a --concurrency= option to the launch. If I use a<BR>
>>> concurrency of 1, the problem does not manifest.<BR>
>>><BR>
>>> Setting the concurrency to 1 to fix the problem isn't an option, but<BR>
>>> makes me think something is getting really mixed up in the select()<BR>
>>> processing in bbnet.<BR>
>>><BR>
>>> Does anyone have any ideas how to diagnose where Hobbit is coming up<BR>
>>> with a 3-second latency, when none of my test tools running off the<BR>
>>> same server can duplicate the same timing?<BR>
>>><BR>
>>> Thanks for any ideas, this is really baffling me.<BR>
>>> -Alan<BR>
>>><BR>
>>><BR>
>>><BR>
>>> To unsubscribe from the hobbit list, send an e-mail to<BR>
>>> hobbit-unsubscribe@hswn.dk<BR>
>>><BR>
>>><BR>
>>><BR>
>><BR>
>><BR>
>><BR>
>> To unsubscribe from the hobbit list, send an e-mail to<BR>
>> hobbit-unsubscribe@hswn.dk<BR>
>><BR>
>><BR>
>><BR>
><BR>
><BR>
> To unsubscribe from the hobbit list, send an e-mail to<BR>
> hobbit-unsubscribe@hswn.dk<BR>
><BR>
><BR>
><BR>
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