Re: Re: endb 101

"Also sprach [email protected]:"
> Quoting "Peter T. Breuer" <[email protected]>:
> > The whole idea of fallover is that you have a "floating IP address"
> > that moves between two machines, according to which of them is acting
> > as the server at that moment. That "primary" (A), when it breaks, passes the
> > IP over to the "secondary" (B), which has an up-to-date mirror copy of
> > the data to serve from.
> 
> ah, i guess i forgot to mention: There Is No Such Thing as "floating IP
> addresses" - at least in my case :-\

Sure there is ...

> machine A and B are located in different hosting centers with static IP
> adresses which i am not allowed/able to change,

That's fine.  It's normal.  In ADDITION to that there is usally a
floating IP address which acts as the front end for all accesses. Or it
could be a dns entry instead of an IP address, but it usually is an IP
address.

You should be able to locate the floating IP on the machines themselves
- it will just be an alias. If you can't locate it on them, locate it
on a third frontend machine which formards to one or the other of them.


> but try to work around this
> issue by using names instead of ip-adresses for my services and have to update
> the DNS records quickly...

OK. DNS will also work.

> > It's also normal to have TWO floating IPs, and TWO resources on each
> > of TWO servers. One resource on each server acts as a remote mirror
> > for a resource on the other server.
> 
> yes, that's the thing that confused me:
> 
>      "One resource on each server (hda3) acts as a
>       remote mirror (nda0) for a resource (md0) on the other server."
> 
> but now i see, that only A will have md0, B will serve from hda3 only.

The situation being described in that passage is a symmetrical setup
where there are TWO resources on each machine and ONE resource on each
machine is a mirror of ONE resource on the other machine.  You can have
that too.  Again, it is "normal".  What you are describing on machine A
and B is one half of such a setup.  If you had another resurce, hda4 on
each machine, you could set up the symmetrical other half too.

> 
> >> i *thought* all machines could
> >> carry an md0. i was wrong. hm.
> >
> > They can, and you are not wrong. There is no reason for B to use a
> > mirror (in degraded mode) while A is running, but it can. It would
> > make things a little easier for when A comes back up again.
> 
> yes, ok.
> 
> i'll look over your other comments with my co-pilot, as there are still some
> requirements we need to sort out on our side. eventually he'll even write to
> the list too ;)

OK.

Peter