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From Mark Montague <m...@catseye.org>
Subject Re: [users@httpd] What is %D in access log meassuring?
Date Thu, 31 Mar 2011 13:51:47 GMT
  On March 31, 2011 9:36 , Janne H <jannehson51@yahoo.com>  wrote:
>> What does 'much "closer"' mean?
> The server is in Amazon EC2 cloud, and ipA is another EC2 instance.
> ipB is from the office, and ab reports a noticeble difference in latency, about 43 ms
when accessing from ipB.

Does "ping" report the same round-trip time when you ping your web 
server from ipA as compared to when you ping your web server from ipB?  
If the answer is "no", then this isn't a problem with Apache.

Also, what does traceroute show beween ipA and your web server, as 
compared to between ipB and your web server?  Again, if it takes longer 
to do a traceroute from ipB, the problem is not with Apache.  And 
traceroute can help you find any significant differences in network 
topology between the two network paths.


>> There is almost zero load on the machines. The EC2 machines are small instances (1
core each) and the office machine a common PC with two cores.
>> They are all running Ubuntu Linux (LTS 10.04 in EC2) and 10.10 in office PC.
>>
>> I'm not sure how to answer about the kernel and networking stacks.

Basically, are there any differences between how the two machines are 
configured?

Since these are Amazon EC2 instances:  are you absolutely positive that 
Amazon is hosting both of them on physically identical hardware?  If ipB 
is on much older / slower physical hardware, that may account for the 
difference you are seeing.   Also, do you have any way of knowing what 
instances from other customers are sharing the same hardware as you?  
For example, if there are more instances sharing the hardware that ipB 
is hosted on, or if the instances for other customers on the hardware 
for ipB are putting the hardware over heavier CPU or IO load, then that 
also could account for the difference you are seeing.

--
   Mark Montague
   mark@catseye.org


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