Hello list users.

I'm struggling with mod_proxy parameters related to amount of open connections 
to backend etc. Here is an excerpt of my configuration:

ProxyPass /exchange/ https://exchange.company.com/exchange/ min=10 max=32 
acquire=10000 keepalive=on retry=5 timeout=15
ProxyPassReverse /exchange/ https://exchange.company.com/exchange/
ProxyPass /exchweb/ https://exchange.company.com/exchweb/ min=10 max=32 
acquire=10000 keepalive=on retry=5 timeout=15
ProxyPassReverse /exchweb/ https://exchange.company.com/exchweb/
ProxyPass /public/ https://exchange.company.com/public/ min=10 max=32 
acquire=10000 keepalive=on retry=5 timeout=15
ProxyPassReverse /public/ https://exchange.company.com/public/
ProxyPass /iisadmpwd/ https://exchange.company.com/iisadmpwd/ min=10 max=32 
acquire=10000 keepalive=on retry=5 timeout=15
ProxyPassReverse /iisadmpwd/ https://exchange.company.com/iisadmpwd/

As you can see, what I'm trying to achieve is a webmail proxy for our company's 
Exchange server. This problem is not tied to Exchange however, I'm experiencing 
the problem described below no matter what server is used a a backend.

First of all, min parameter seems not have any effect. When I start Apache, 10 
connections are not opened to backend immediately. From documentation:

min: Minimum number of connections that will always be open to the backend 
server.

From that, I would conclude that it should keep 10 connections always opened, 
no matter what. However, using netstat -atpn I can see that connections are not 
opened always, but instead only during activity from the clients.

Second problem is keepalive. From documentation, I understand that this 
parameter should cause connections once opened to be kept open. This seems not 
to be case; after activity, connections are kept open for some time, but no 
keepalives are sent. I have verified this using wireshark. As a result, backend 
server soon resets the connections, and they have to be opened again upon new 
activity.

I have also notices the same behavior with both prefork and worker mpm's. 
Currently prefork mpm is in use:

   StartServers         10
   MinSpareServers      10
   MaxSpareServers      20
   MaxClients          256
   MaxRequestsPerChild   0

I'm starting to think that I have understood something completely wrong here. I 
would be thankful of any hint about what might be going on here.

Regards, Petteri Heinonen

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