[hobbit] Debugging help: bbtest-net gets http test timing wrong

Tim McCloskey devzero at cox.net
Mon Jun 16 06:13:43 CEST 2008

I'll take a stab at this but you may have already looked at the things I wonder about or they may not help in any way. 
I've only thought about this for a couple of minutes so I could be way off.

You have stated there are a couple servers that seem to respond differently.  Can you, 100% consistently, recreate the 
proper|improper response from the web boxes?  If so, look at the changelog between apache 2.2 and 2.0 (assuming that 
those servers - 2.0, 2.2 - are on the same network and that all of the media setting match ie. 100Fdx 100Fdx, etc.).

Are you _sure_ you are not using DNS in some fashion, perhaps reverse lookups or perhaps the newer apache config file 
contains some lookup setting.  (can you get away with using the same httpd.conf on the 2.0 and 2.2 boxes?)

What does the network traffic and connections look like on each of the servers?   Have you tried running tcpdump on one 
of the web boxes to see if there are any clues there?

I don't recall if hobbit uses wget for his http gets.  Are all the servers using the same settings in resolv.conf and 

There are probably other things to check but start with making sure DNS is not involved, even if you think it is not.

Alan Sparks wrote:
> Continuing to try to debug this problem, have tried about everything I 
> can to resolve the issues with http probes.  Including:
> * Complete rebuild of the server with CentOS 4.6 and recompile of 
> Hobbit.  Same issues.
> * Removing everything from /etc/sysctl.conf, rebooting.  Same issues.
> * Manipulating the httpd.conf configs on remote servers, forcing 
> HTTP/1.0, removing ETags, creating a very simple index page to test 
> against.  Same issues.
> * Upgrading Apache on sample remote server to Apache 2.2.8 (most are 
> 2.2.4).  Same issue.
> * Recompiling Hobbit with debugging flags, to make sure the optimizer is 
> not applied.  Same issue.
> The only two servers I have that seem to work consistently well are a 
> pair of Apache 2.0.52 servers.  The 2.2.4+ servers all seem to give 
> Hobbit issues.  Although, again, repeated curl or wget probe cycles 
> against the servers from the Hobbit server never show more than a 0.2s 
> response time.
> But, Hobbit continues to report things like:
> - OK
> HTTP/1.1 200 OK
> Date: Mon, 16 Jun 2008 00:54:03 GMT
> Server: Apache/2.2.8 (EL)
> Last-Modified: Sun, 15 Jun 2008 00:37:00 GMT
> ETag: "7c809f-9b-44fa9b5806300"
> Accept-Ranges: bytes
> Content-Length: 155
> Connection: close
> Content-Type: text/html; charset=UTF-8
> I can't come up with anything other than Hobbit as a cause. But is there 
> anything I can do to trace what is happening internally to get past this 
> problem?  Any ideas at all would really be appreciated.  Thanks in advance.
> -Alan
> Seconds:     3.00
> Alan Sparks wrote:
>> Have a new install of Hobbit (4.2, tried 4.3 snap as well) on a fresh 
>> install of CentOS 4.6 x86_64, up to date on patches.  I have a problem 
>> with HTTP tests on "random" web servers that I just can't figure out.
>> I have about 64 of my hosts in the bb-hosts on this server, and have 
>> http tests defined for these servers.  On most of these servers, 
>> Hobbit is reporting the "Seconds:" for the response at 3 seconds.  It 
>> seems that it is inconsistent -- one cycle to the next, the 3-second 
>> response may move to a different set of servers.
>> The http: tests are defined using the IP address of the server - no 
>> server name (so no DNS lookup).
>> I've run a loop of tests on the same URL using wget and with curl, and 
>> used my browser and Telnet to connect to the same URL.  I consistently 
>> get a response time of about 0.2 seconds maximum from the servers.
>> The bbnet entry in hobbitlaunch.cfg looks like:
>> CMD bbtest-net --report --ping --checkresponse --debug
>> With the debugging turned on, I see the following entries periodically 
>> in the network test log:
>> Address=, open=1, res=0, err=0, connecttime=0.002965, 
>> totaltime=3.006810,
>> Address=, open=1, res=0, err=0, connecttime=0.002956, 
>> totaltime=3.007413,
>> Address=, open=1, res=0, err=0, connecttime=0.002860, 
>> totaltime=3.007120,
>> The problem does not affect the same hosts each time.  The problem 
>> will show a different number of hosts usually each cycle, sometimes on 
>> same servers, but often on different ones.
>> I've tried the following to see if anything will help:
>> * Reducing the number of hosts.  If I only have a couple or three in 
>> the bb-hosts, the problem doesn't manifest.
>> * Recompiling.  Doesn't help.
>> * Changing the test URL.  Doesn't help.
>> * Adding a --concurrency= option to the launch.  If I use a 
>> concurrency of 1, the problem does not manifest.
>> Setting the concurrency to 1 to fix the problem isn't an option, but 
>> makes me think something is getting really mixed up in the select() 
>> processing in bbnet.
>> Does anyone have any ideas how to diagnose where Hobbit is coming up 
>> with a 3-second latency, when none of my test tools running off the 
>> same server can duplicate the same timing?
>> Thanks for any ideas, this is really baffling me.
>> -Alan
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