httpd-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Rainer Jung <>
Subject Re: OS Keep-alive on forward proxy
Date Thu, 05 Aug 2010 07:56:46 GMT
On 05.08.2010 05:45, Ryujiro Shibuya wrote:
> Hi,
> Can you tell if the OS Keep-alive feature should be expected to work on
> forward proxy?
> The mod_proxy of latest httpd 2.2 and trunk (2.3) has OS Keep-alive
> (Keep-alive connection to origin server) feature, but it seems not working
> when we configure the httpd as the forward proxy server.
> If the client connection is kept alive, the proxy sends indeed "Connection:
> Keep-alive" to the origin server but the proxy doesn't actually try to keep
> the OS connection alive; it closes the OS connection immediately after
> receiving the response.
> The inconsistency between sending "Connection: Keep-alive" and immediate
> connection closing looks like a defect (and I've just posted a bug report
> 49699). But apart from the inconsistency, I wonder if the OS Keep-alive of
> mod_proxy is designed to work for the forward proxy in the first place.

OS Keepalive and HTTP Keepalive are two totally different things.

OS Keepalive: if a connection is open but idle for a long time 
(configurable), then the OS automatically sends empty TCP packets over 
the connection in OS dependent intervals.

HTTP Keepalive: Signalling via HTTP "Connection" header, whether the 
connections is supposed to be kept open and eventually reused for 
another HTTP request/response.

OS Keepalive does not imply HTTP Keepalive. For all reasonable 
configurations (except possible server to server communication), HTTP 
Keepalive timeout will be much shorter than the minimum idle time, 
before OS Keepalive packets are send. So OS Keepalive for most HTTP 
communications is not relevant.

And yes: the forward proxy does *not* do HTTP Keepalive. Technical 
reason: the connections to the origin server are pooled and retrieved 
from and returned to the pool for each request. A forward proxy usually 
talks to many diferent origin servers. Keeping those connections open in 
a naive way would lead to a lot of not well used pools. Assuming that 
during one client connection the origin server often is used for 
multiple requests this could be improved, but would bloat the already 
complicated proxy code even more.



View raw message