Re: [PLUG] network choice from the application level

[Matt Mossholder <matt@mossholder.com>]

On Thu, Feb 16, 2012 at 10:09 PM, Eric at Lucii.org <eric@lucii.org> wrote:
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> Suppose:
>
> 1. I have two applications running on an OpenSuse server.
> 2. This OpenSuse server has one NIC and two IP addresses.
> 3. There is a database server in the same network
> Â that has a *single* IP address.
>
> Is it possible for the applications (PHP) to select which of the two
> OUTGOING IP addresses it uses to talk to the database server?
>
> The database people want the requests to come FROM a different IP
> address depending on the particular application.
>
> I think it's impossible.
> I told them to get another IP address for their database server and
> then I can do it :-)
>
> Anybody know if it's possible?
>
> Eric

A quick Google suggests that PHP always uses the IP that has the
shortest path to the destination when sending packets, so you are
going to have to do something "outside the box".

A few things come to mind, in order of preference based on my
impression of load:

     1) There might be some things you could do with cgroups and/or
Linux Containers (LXC) to mask out the IP addresses from the apps so
that the only ones available are the ones you would like them to use,
     2) iptables and NAT can be of use, as Doug suggests,
     3) run a local reverse proxy (or even something like ncat), bound
to localhost on a port for each app, and then have it establish the
connections using the correct IPs for sources.


     --Matt
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