Setting up 2 physical redundant servers

[rado]

Wow, Bob, this is awesome...first thing I did was copied this to a file 
/home/rado/bobsHAsetup as to keep it's entirety. Thx for this. 

I have been looking around the web at HA stuff and really hard to see
the forest because of the trees and it seems that you already have setup
what I want to do!
Reading thru this I keep asking myself why this couldn't apply to what I
am doing. Can you see why this wouldn't do it?
I want to try your config here if you don't mind.
gotta pick thru it first tho...
> John,
> 
> HA info:
> 
>         http://www.linux-ha.org/
>         
> You might want to look into this before trying to roll your own.
>         
> What I did:
>         
> I am at the Kennedy Space Center, and what we did was a somewhat dumbed
> down version of HA and heartbeat.
> 
> I have two machines, essentially web servers for MRTG.
You use the term MRTG and the definition I get is Multi Router Traffic
Grapher, a tool to monitor the traffic load on network-links. Is this
what you mean is this instance?
>   Each machine has
> two ethernet interfaces.  The eth0 interfaces are connected to a common
> switch, the eth1 interfaces are connected together via a crossover
> cable.  

I understand this and think I have the hardware on hand...nope gotta
hustle up a crossover

> At any given time, only one machine is active.  It remains active as
> long as it can ping the upstream router.  If it fails to ping the
...upstream router...in my case the zoom???

> upstream router (tries every 10 seconds) it will send a command via rsh
> or ssh thru the dedicated link to the slave telling him to become the
> master.  Both machines also ping each other via eth0 and eth1 and if the
> slave determines that the master is not responding (loses both paths) it
> will automatically assume the master's role.
> 
> All interfaces have unique IP addresses.  The eth0 interfaces are
> visible to the world, but the eth1 interfaces are only visible to each
> other.  The eth1 channel is used to issue remote commands between the
> two boxes.  The master will also have an aliased IP address on eth0 that
> is DNS registered and used by the rest of the world to access the server
> (that was the key!).  When a switch-over occurs, that aliased address is
> removed from the master and added to the slave.  This is where ARP
> caching becomes a problem.  We have Cisco routers upstream and the ARP
> caches need to be cleared before traffic will pass to/from the aliased
> IP address.
> 
> The router's ARP cache can be cleared with:
> 
>         ping -q -c 1 -b -I $COMMONIP $NETWORK > /dev/null 2>&1
> 
> Where $COMMONIP is the aliased IP address and $NETWORK is the network
> mask.  I don't how to do this for any other network gear (i.e your
> modem).  That was the other key!

I will have to check into this and my equip.
> 
> The master-to-slave and slave-to-master decision tree is pretty
> convoluted and more than likely will be different than yours.
> Essentially, whichever machine can see the most (via ping) is the
> master.  If both see everything, then the one designated as the master
> is the master and the other is the slave.  As long as the dedicated link
> is up, the one becoming the master can tell the other, via rsh, ssh,
> etc.  A background script runs on each machine every 10 seconds that
> does all of the pinging.
later on I will need to talk over the scripts w/you please
> 
> Somewhat confusing, but I hope it helps.
> 
> Bob...

rather than look and scour the web and go blind trying to decide which
way to go I think I would like to try your config if you don't mind. 

Bob, how are you achieving redundancy between the 2 boxes??

btw, a very confusing issue and you really presented it like it was kids
stuff!


thx,
john rose

-- 
rado <rado at rivers-bend.com>