[Linux-cluster] Cluster Planning

[Rainer Duffner]

Scott Kellogg wrote:

>
>>
>> Also to use an active-active (same service active on both servers) 
>> configuration + loadbalancing you will need more than 2 servers; at 
>> least 4 servers, 2 for loadbalancing (1 active/1 backup) and 2 for 
>> the critical service active concurently on both servers (no high 
>> availability, no failover).
>
> You seem to be referring to LVS.  Right, I can't implement that since 
> I don't have enough hardware.  I think that active-passive will be the 
> way to go.  When the active node dies, the passive node will take 
> over.  The data will only be as fresh as the last synchronization.  
>
> That begs the question of what happens when the active node comes back 
> up ... will the passive node (now active) sync its data to the new 
> active node?  This is where picking a synchronization method becomes 
> vital.


That's where GFS comes in.

I don't want to sound rude, but either you (or your customer) have the 
budget for a cluster or not.
If you don't have the budget, it's better to just use the 2nd server as 
hot-spare and rsync the data over to the 2nd one and do the failover by 
hand (and even more so the re-activation of the primary server)
Or you should have bought a more expensive, more reliable server instead 
of two low-end ones.
You *can* have low-end servers, but you need a reliable 
storage-infrastructure (which will be a SAN in 7 out of 10 cases and 
iSCSI in the other), which has a big upfront-cost.

This always reminds me of people who want to drive cars they cannot 
really afford.
It's better to acknowledge that and accommodate to a cheaper car than 
sitting there one day without the money to have it repaired....



cheers,
Rainer