manfred wrote:
> Hi everybody,
>
> What I'm wondering, are all these qmail-ldap installations without any
> 'hot-standby'? How are you maintaining your machines if you can't take them
> out of the service? What about failure of your machine? I guess I'm missing
> something here?
> Maybe someone has a 'hot standby' solution working somehow and could
> enlighten me?
> Thanks a lot!
- All of your user accounts are in an LDAP servers so that any mail server can
access that info. The LDAP database is replicated for load-balancing/HA.
- The mail servers are the middle-men. They write mail to shared storage that's
mounted from an external fileserver.
- The external file storage is something like an NFS server, or all your servers
are in a SAN, etc... You might have a clustered NFS service for HA.
- On the front, you have a Layer4/7 switch that directs the mail coming in.
Using service checks, it knows if a server is removed and directs mail away from
that server. There are many commercial solutions available (f5, Alteon, etc.),
or you might be able to roll your own using something like the linux virtual
server project. Also, this device can have a failover node for HA. Every mail
server for a particular domain shares the same IP which is made possible by the
smart switch.
If a server fails, you can pull it out without a problem. Fix it, reinsert it,
or just replace it... doesn't matter. The middle servers are all clones of each
other. Depending on your setup, you might need to replicate some info between
them, but most everything can be shoved into the LDAP server.
Heck, if everything fails, smtp servers on the rest of the Internet are designed
to deal with network outages. If you have only one mail server, you can usually
take it down for a few hours for maintenance without adverse effects. The worst
that can happen is that people will get a failure response and have to resend
their spam to you ;)
Good Luck,
--
Clint Bullock
Network Administrator
University of Georgia
Office of the Vice President for Research
