Re: A Few Questions

[James Bourne <jbourne@MtRoyal.AB.CA>]

On Fri, 5 Apr 2002, Geoff Silver wrote:

> > I think you need to look for some load-balanceing or clustering solution
> > (Turbo Linux?) to do this.  slapd as far as I know does not have a "fail
> > over" method,  which is what it sound like you are actually looking for.
> 
> Wow, I'm surprised there isn't the ability to do this.  So slaves are only
> really good for load balancing, not really redundancy (except manual
> failover).
> 
> Hmmm.  I wonder if libnss-ldap, libpam-ldap, etc contain (or could
> contain) code to fail over to a backup if the master is down.  Not quite
> as efficient, since the list of backups would have to be given to every
> application, but would still provide for some redundancy.
> 
> Has anyone considered adding this sort of functionality (is it even in the
> protocol specs?)  Since the master knows what slaves exist, it would seem
> to make sense that a client could cache a list of slaves from the master.
> This sort of redundancy would seem to be a killer in a large scale
> corporate environment.  Just a thought.

Take a look at the lvs project (www.linuxvirtualserver.org).

You can use this in two different modes, first using it as a redirector
service (using piranha) and second as a fail over service (lvs on a slave
would monitor the primary, then if the primary fails, the slave picks
up the virtual IP of the primary and acts as primary).

Configuration shouldn't be too difficult, just use a multimaster
configuration.  The only thing that may be a problem
is arp timeouts, but this can be covered by piranha as
it has a sendarp program with it.  

BTW, this can be used for almost any service which requires high
availability.  

Another project which may also work or might be good for
additional information is linux-ha.org. lvs actually uses parts from the
linux-ha project.

Regards
James Bourne

> > No such document exists, AFAIK.  Sad.  I cover some of this in my LDAP
> > presentation, and I hope to add more,  but it is FAR from exhaustive.
> > ftp://kalamazoolinux.org/pub/pdf/ldapv3.pdf
> 
> Cool.  Thanks!
> 
> 

-- 
James Bourne, Supervisor Data Centre Operations
Mount Royal College, Calgary, AB, CA
www.mtroyal.ab.ca

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