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> The VIP is the address which you want to load balance i.e. the address of
> your website, this is not the IP of any of the boxes normally it's the
> 'Virtual IP (VIP)' and as such is just put onto the back of another LAN card
> as eth0:1 or whatever, the main reason I see for this is so that it (the
> VIP) can be swapped between two directors if a fault is detected on one.
>
> Just how I see it.
This is correct. VIP stands for "virtual IP", and it is the IP address
of the "service", not the IP address of any of the particular systems
used in providing the service (ie the director and the realservers).
Not only can the "service IP" (the VIP) be moved from one director
to another if a fault is directed (typically this is done by using
mon and heartbeat, or something similar), but a director can also
host/balance more than one virtual service. You could have HTTP/HTTPS
balanced using one VIP, and FTP service (or whatever) balanced using
another VIP, and these VIPs can be be on the same system, or different
systems, at different times.
The realservers also have to know about any VIPs they are involved
with, so they will accept any IP packets they receive with that
destination address. So, you have to put the VIP on any realservers
that will be used, as well as configuring the director to use. This
brings up some ARP issues that are addressed on the LVS home page:
http://www.linuxvirtualserver.org/Joseph.Mack/HOWTO/LVS-HOWTO-3.html
Also, there can be persistence issues, if you are using cookies or
https, or anything else that expects the realserver fulfilling the
requests to have some connection state information. This is addressed
here:
http://www.linuxvirtualserver.org/persistence.html
Here are some links you may find helpful:
http://www.linuxvirtualserver.org/Joseph.Mack/HOWTO/LVS-HOWTO.html
I had hoped to find a link explaining how VIPs work, but I didn't
find any with a Linux context. I could point you to some Veritas
Cluster Server 1.3 or Sun Cluster 3.0 documentation, but the links
are to the whole PDF file for a large manual, and thus the links
would probably be more distracting than useful.
--
John Cronin
mailto: `echo NjsOc3@xxxxxxxxxxx | sed 's/[NOSPAM]//g'`
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