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failover software

Posted on 1999-07-28
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Last Modified: 2010-04-21
I will have to work on developing a failover software which
identifies that a active system is down and statdby should
become active.  
I think of a tcp/ip connection and send messages at a regular interval and  if missed at one
system, it could be either system down/ connection broke because of interface down.  how do we make sure that the interface is down in the local system or in other standby system.?

Is there any algorithm to acheive this failover?  Is there any other way for finding out other that TCP/IP messaging?

I would really appreciate if any one suggest me some ideas.
thanks
ramalaks@peri.com
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Question by:ramalaks
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by:ramalaks
ID: 2011727
OS: solaris 2.6
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marpon earned 300 total points
ID: 2011728
The failover subject is nothing trivial, but here are some conclusions I can give you after beeing working with comercial software that achieves this:

- you must have redundant ways to comunicate between master and slave. Suppose you can determine wheter you 're local interface is ok. If communication between both servers is broken (for example, the hub fails), both servers will believe the other one is to blame, the slave with wake up and you 'll have two servers doing the job.

- Having redundancy (I mean, two interfaces in each host, two cables, etc)., you can always check connection by the other interface. In addition, in case of network interface failure, you can decide wheter you 'll switch to the slave server
or just switch to the backup interface.

- You can always have other ways of telling the other server "I 'm alive" if you have something beeing shared by both servers. For example, I can tell you the case of software from HP, where you have two servers that are both connected to an external disk array where they share information. In case the "heart bit" stops, they  look into a portion of the disk to see if the the other one is still alive.
 
 This is mine, I think you can do something similiar with a database server to which both have access, etc.

I think this is all there is to say about "heart bits" and detecting failures of the master, but I can share some experiences about general failover, if you whish.

Regards
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by:ramalaks
ID: 2011729
I have decided something similar to your concept. we have on active and more that one standby.  when active dies, any one of the standby becomes active. we have to have a common place to share the info for which we have DB server.  

I am not very much experienced in this area. so I just want to make sure that This idea is ok.

I am definitely intested in knowing experiences about general failover and heart beats.  You can email me or post here as comment.

thank you for your answer.

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