[users@httpd] mod_proxy_balancer - no way to name pool members by IP.

[df...@white.u-net.com]

I've hit a vexing impasse with mod_proxy_balancer.

I have a pool of backend boxes. They vhost many domains, so
need the specific Host: header in requests to them (the *same*
Host: header for all of them)

I proxy reqeusts to them potentially thousands of times a second,   
and their IP's are not going to be changing, so I name the
BalancerMembers by IP address, as the DNS lookup overhead is 
a fatal waste of CPU, especially if your DNS servers melt
and your site dies unnecessarily. (No, /etc/hosts is not possible.
The sitename has multiple A records, and I make the backends choose
individualiseable vhosts. Besides, my hosts file is vast!)

Unfortunately, when I try and use mod_headers to set the Host: header
for these backend connections, the balancer layer destroys the
result and replaces it with the IP.

Apparently, if I switch ProxyPreserveHost on, I may get further,
but since that's a site-wide setting a side effect would mean all
of my other proxied directories would now get the wrong Host: header.
All the RewriteRule [P]'s would break and I would have to catch and
replace the Host in every single one of them in individual <Proxy> blocks.
That deluge of perpetual kludgery does not appeal.

What I need is a way to tell a ProxyPass or BalancerMember, that
they should use a certain Host: header in its communications
with this backend. e.g.
BalancerMember http://10.0.0.1/foo/ host=foobar.com

The logical alternative would have been to be able to specify a
certain target IP to connect to instead of a certain Host name
to use e.g.
BalancerMember http://foobar.com/foo/ address=10.0.0.1

but I suspect apache would then be unable to set <Proxy> block
rules for individual balancer members since they'd all declare
the same URL and you'd be unable to match them individually

So, I currently can't use my backends in mod_proxy_balancer

Does anyone have any suggestions?

DFW


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