We handle our development and production apache servers as follows (on Sparc Solaris 8, E250, 1 GB ram) using a single box. While we have enabled mod_perl on some of them for prototyping we haven't deployed any operational mod_perl code yet. YMMV though I have proven the concept.

Our single server has multiple IP addresses configured, say 122.133.99.10, 122.133.99.11, 122.133.99.12, 122.133.99.13, 122.133.99.14, etc. These all happen to be on the same subnet.

We install apache 1.3.xx and with --enable-shared=max then add several apache modules (including mod_perl) by building outside the source tree with APXS.

Then we have apache installed at /opt/apache-1.3.xx/(...) but I don't run it from that location. I create directories (one per plane ... plane is our term for an instance of apache: the conceptual equivalent of a vhost but planes each have independent pools of children) named: /opt/planes/dev_server1 , /opt/planes/dev_server2, /opt/planes/production , /opt/planes/beta, etc, etc.

Each directory in /opt/planes consists of

|_
  dev_server1 - (apachectl)
  |_ 
    conf - (httpd.conf)
  |_
    logs - (httpd.pid will be created here)
[download]

Each plane's httpd.conf file uses the BindAddress directive to limit it to a single IP address. Each Plane has its own document root, script alias, and enabled set of modules. Each plane has its own user directive. Each plane is started/stopped independently via its own apachectl. Some of our planes load mod_perl, some don't.

Advantages: Fully independent instances of apache each running unique sets of modules. Each can be started/sopped independently. This technique also avoids the suexec limitations of vhosting: Any developer in the dev group can place code in our integration plane using his or her own account(not production though)

Disadvantages: Memory usage, although using separate hosts for apache servers uses even more :)
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"That is the best engineering, not which makes the most splendid, or even the most perfect, work, but that which makes a work that answers the purpose well, at the least cost"
--Ashbel Welch, President ASCE 1882