Forward from one LVS instance to another?

[Robin Bowes]

Hi,

I'm running pulse/LVS to balance http/https traffic.

I have identical setups in two DCs (with different IPs, of course).

DC A looks like this:

TCP  $IP_A:http
  -> a048:http
  -> a046:http
  -> a044:http

And DC B is the same, with a different IP:

TCP  $IP_B:http
  -> b048:http
  -> b046:http
  -> b044:http

I'm using Direct Routing, and have an iptables REDIRECT in the *nat
chain on each of the real servers.

In DC A:

-A PREROUTING -p tcp --dst $IP_A -m multiport --dports 80 -j REDIRECT

In DC B:

-A PREROUTING -p tcp --dst $IP_B -m multiport --dports 80 -j REDIRECT

This all works just fine.

Now, DC B is currently the "live" DC but we are planning a cutover to DC
A. One of the things that this will involve is changing DNS records to
point at $IP_A instead of $IP_B.

The DNS change will take a while to propagate so I want to forward
traffic that hits $IP_B after the cutover to $IP_A.

What I thought I'd do is to simply specify $IP_A as the only real server
of the LBs in DC B, ie:

TCP  $IP_B:http
  -> $IP_A:http

However, this doesn't seem to work. So, I thought about it some more and
figured I'd have to add a REDIRECT with the address of the original IP,
eg. in DC A

-A PREROUTING -p tcp --dst $IP_B -m multiport --dports 80 -j REDIRECT

This didn't seem to work either.

So, at this point I'm stumped. Anyone got any ideas how to make this
work? Is this sort of thing possible with Direct Routing?

R.