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Please correct me, but my understanding is that with software load balancing a service must be run on each server while there is one DS that notifies the other servers that a server has gone down and that they should consume that servers load.

With hardware load balancing what happens in a fail-over? Could someone explain? Is there advantages with using hardware load balancing when it comes to fail-over, or is there advantages with software? Or do they both have their pros and cons?

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Possible Duplicate: Hardware vs Software load balancers: Just a cost issue? –  Alex Nov 30 '12 at 3:41
    
Not a duplicate. This is asking HOW hardware loadbalancing/failover works –  FabianCook Nov 30 '12 at 3:51
    
Eh, it's pretty much a duplicate as you're both running under false pretenses. Hardware devices just run software; it's a whole stack as opposed to parts of a stack. The other Question outlines this pretty well. I'm not going to hammer this as Alex has a good answer and the community can decide. –  Chris S Nov 30 '12 at 4:46

1 Answer 1

First off, Fail-Over and Load Balancing are two different things.

Fail-over is having two devices or servers, one active and one passive. When the active fails, the passive detects it, for example using CARP or VRRP, and takes over the active role.

This is used mainly with firewalls, routers and other networking devices.

Load Balancing is having many devices that are all active and are receiving their share of a load.

That being said, software or hardware load balancer will work pretty much the same. They both have pros and both have cons.

Having hardware load balancer means adding devices to your network, that means taking time to maintain these devices, implement the devices, having spaces and electricity for the devices, so on and so forth. If you only add one load balancer, then you just added a single point of failure on your network.

But, having two robust hardware load balancer can offload your servers (with SSL acceleration for example)

Both will usually use VIPs to present the service on one IP and then distribute the load between members.

If one of the members fails, it will be temporarily taken out of the "VIP network" and stop receiving it's share.

This can be done by CPU load, RAM load, network load, network latency or simply in a round-robin mode.

But it's not limited to that.

Hope this helps.

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Yes, but how do they vary and how does a software failover work compared to a hardware? –  FabianCook Nov 30 '12 at 7:34
    
At this point I don't know what information can be added to my answer or the answers I linked to in my first comment. Sorry. –  Alex Nov 30 '12 at 14:08

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