Hi.
Heartbeat is usually a private network between the nodes, used to send data 
about which nodes are alive. You'll want a low latency network for this. Google 
for clusters and heartbeat and you'll find lots of information I'm sure.
 
Clusters can be used as High-Availiblity where server B is indeed just a 
backup, but it can also be used as High-Performance where two or more servers 
share the requests between them. Obviously the performance will degrade if 
parts of that cluster goes down. So yes, B can both be a backup and an equally 
performing server, depending on your setup.
 
I'm a bit out of my compentence area here as I haven't done webserver 
clustering, but I do believe the general principle is about right. I'm sure 
someone on this list will correct me where I'm wrong.
 
Cheers,
 
Oscar

________________________________

Från: Ch Praveena [mailto:[EMAIL PROTECTED]
Skickat: ti 2008-04-08 10:47
Till: users@httpd.apache.org
Ämne: Re: [EMAIL PROTECTED] Split-brain problem.


Thank you Oscar,

  As I am new to clustering Tomcat, Let me  know some information about 
Heartbeat too.. 

And according to your information, Is that Server B a backup for Server A(So 
that when A fails, B attain its responsibilites) or an equally performing 
server with A.




2008/4/8 Oscar Haeger <[EMAIL PROTECTED]>:


        From my experience with clustering that is when the connection between 
parts of the clusters are lost and they can't agree on which one is supposed to 
keep serving the data. The most common way around it afaik is to have a 
priority and heartbeat between the nodes and allow them to kill each other off 
(something like STONITH = Shoot The Other Node In The Head) or similar.
        
        So, if we have two servers A and B and a heartbeat (with STONITH) 
between them and node A misses a few heartbeats (perhaps a lockup, perhaps 
something else), then node B will reset node A and take over that nodes 
capabilities.
        
        This is without reading about Terracotta so things might be different 
there, but that's the split-brain problem from my experience.
        
        Hope this helps
        
        Cheers
        
        Oscar
        
        ________________________________
        
        Från: Ch Praveena [mailto:[EMAIL PROTECTED]
        Skickat: ti 2008-04-08 09:30
        Till: users@httpd.apache.org
        Ämne: [EMAIL PROTECTED] Split-brain problem.
        



        Hi all,
        
          While going on with Terracotta article,
        -- 
http://www.terracotta.org/confluence/display/explore/How+Terracotta+Works,
        For implementing application server clustering, I found this phrase, 
"Split-brain problem."..
        
        Please let me know about this in detail..
        
        
        
        Regards,
        
        Praveena Chalamcharla,
        Securview....
        

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-- 
Regards,

Praveena Chalamcharla,
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