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From Fabien Duranti <>
Subject Reverse proxy and large HTTP requests
Date Fri, 05 Sep 2014 22:51:33 GMT

I am running a proof of concept with ATS 4.2.2 in reverse proxy mode to 
improve user experience when accessing a web application over an high 
latency link ( 255ms RTT )

The setup is the following :

client -> ATS1 --- High latency link --- > ATS2 -> origin_server

all connections have SSL.

Everything behaves as expected when client requests are small, response 
times when connections are established pretty much correspond to RTT + 
origin response time + the negligible ATS processing time.
However, when requests are bigger than something around 3000bytes (POSTs 
typically), reponse times are  looking more like 2x RTT + origin 
response time.
Running a network capture showed that when ATS1 sends a big request, 
there are on the wire 2x 1500bytes packets sent, then wait for ATS2's 
ACK, then another small packet to send the remaining of the request. 
That wait for the ACK pretty much makes response times mutltipled by 2.
I immediately thought about the TCP tunning of the operating system 
(RHEL6) could be wrong but running the exact same request with curl on 
ATS1 wouldn't show that. on the wire we would rather see two fragmented 
packets of 2650bytes + 800bytes and the response from ATS 2 comming 
shortly after the RTT.

Is there any misconfiguration in ATS that would explain this ?I tried 
proxy.config.ssl.max_record_size  = 0 then 1000, then 4000 but didn't 
see any difference

Thanks !

Fabien Duranti

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