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Having read through the list archives looking for a solution to my
problem, it seems as though variations of this request have been posted
a few times over the last few years without success. However the
posters expressed their problem in rather unclear terms. I will attempt
to describe it more clearly.
I am trying to load balance to two "real" servers which are actually
listening on virtual IPs on the load-balancing host. Why would I want to
do this?
To build a test environment for a web application which usually runs on
an IPVS cluster. The purpose of the test environment is to test for
database/cache contention issues before we deploy to our production
cluster. The catch is I must make the test environment (lvs director + 2
x application server instances) run on one physical host (each
developer's development machine).
The man page for ipvsadm makes specific mention of forwarding to real
servers which are in fact running on local interfaces stating that the
load balancing "forward" mechanism specified for a virtual service is
completely ignored if the kernel detects that a real server's IP is
actually a local interface. The "Local Node" page describes a
configuration in which I could load balance between a "real" server
running on the director's virtual service IP and a real server running
on another host. This does not solve my problem however as I must bind
each instance of my application to a different IP address on the same
physical box.
You may be thinking "Why not run the two instances on different ports on
the same IP (the virtual service IP)?". Sadly the application is not a
simple web-site, and source code and deployment container dependencies
on certain port numbers exist. eg RMI-IIOP listeners.
Does anyone know of some config or kernel hack, patch or whatever which
might make my ipvs present forwarded packets to the virtual interfaces
as though they had appeared on the wire so that my forward directives
are not ignored and the packets are not simply presented to the TCP
stack for the virtual service IP? I guess this is like NAT to local
destination addresses (as opposed to NAT of locally originated
connections which is supported in the kernel).
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