[CentOS] Two Instances of Apache; Primary IP / Secondary IP

[mouss]

Al Sparks wrote:
> Tried the apache group, and no response.  Thought I'd try here.
>
> I have set up a development environment so that it mimics a production
> environment.
>
> The production environment has a proxy server (apache 2.x) that sends
> requests onto another back-end apache server, and of course the proxy
> server serves up pages sent by the back-end.
>
> All that works fine.
>
> However, in my development environment, I thought that I'd set up a
> separate instance of apache on the same server, and add a secondary IP
> address on the same interface.
>
> The proxy apache instance listens on the secondary IP, and the
> back-end instance listens on the primary IP.
>
> When I send a client request to the proxy, I get a blank page.  When I
> check the logs, the back-end shows requests coming from the primary
> IP, and not the secondary IP.
>
> My conclusion is that the proxy is sending its outbound traffic on the
> primary IP address, not the secondary IP address it's listening on.
> That in turn means that back-end is sending its pages back on the
> primary IP instead of the secondary, and that means the proxy instance
> isn't receiving answers to its request.
>
> I know that BIND can be configured to send requests on secondary IP
> addresses.  Can Apache?
>   

do you mean making apache use a specific IP when it proxies the request? 
(you really lost me, so I may be misunderstanding). why do need that at 
all? whatever IP is used should not matter since the backend will reply 
over the socket that was opened by the proxy (be it a production proxy 
or the test proxy).

otherwise, the IP is selected by the kernel depending on the 
destination. so if you use something like
ProxyPass / http://10.1.2.3:8080/
in one proxy and
ProxyPass / http://10.4.5.6:8080/

each will use the "selected" IP.

> Is there something I can do with routing tables that can help?
>   
That would require "advanced" routing. standard routing is based on 
destination and the source IP is selected by the kernel after the route 
has been computed (this allows setting the right IP should you have 
multiple network interfaces...).

but you should not need this.