Re: Ideas on Failover/Load Balancing

[rader]

 > >> I'm planning on deploying a server soon that will be a mirror of my
 > >> masterhost.   Would anyone be willing to provide some details on
 > >> how they've gone about the process of deploying a server for
 > >> failover/load balancing?

Keep in mind that there's really no such thing as "masterhosts".
There's "policyhosts" and there's systems listed on the RHS of
server= blocks in copy: actions (which I call "file servers".)
Policyhosts are just file servers that serve up /var/cfengine/inputs
via update.conf.


 > > You have a couple of options.
 > > 
 > > 1: Use some sort of network appliance to do the load balancing.
 > > This means you'll have to have the same private key on each host
 > > or clients will be confused. Also keep in mind that connections
 > > coming in from the master server to the clients may come from a
 > > different address then the virtual ip. I think the applicance
 > > would have to be transparent, otherwise the server will get
 > > confused as to the clients ppkey.
 
 > Are ppkeys hardware dependent?  That is, if I have a system failover (move)
 > to another box (ie. new hardware box, but everything else the same), is it's
 > ppkey going to be different?  

The ppkey is just a file--and you certainly don't want it to be
different!  Restore /var/cfengine (including the policyhost's ppkey)
and cfengine will pick up right where it left off.  I did that just
last week (new OS, but the same hardware.)


 > I've been thinking about this issue with
 > respect to moving virtual machines around to different hardware boxes.

It seems to me that manual failover of the policyhost would be
super easy: 

 - configure the backup-policyhost to get a complete 
   mirror of /var/cfengine/masterfiles.  

 - make the ppkeys on the primary-policyhost and 
   backup-policyhost the same.

 - when the primary-policyhost dies, renumber the 
   backup-policyhost to the primary-policy 

(This is a strategy I've successfully used for master/primary name
server failover for about 18 years now.)

I would think the same idea goes for file servers--except replace
/var/cfengine/masterfiles with the source part of all your copy:
blocks statements.

There's OSS software out there that'll automatically reconfigure a
backup host to take over (e.g. change it's IP address) for a primary
host when a primary host dies, right?  Anybody have recommendations?

steve 
- - - 
systems & network manager
high energy physics
university of wisconsin