apache 2.2 / mod_proxy / parameters

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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