[Wylug-help] The recent Xen talk - a question...

[Chris Myers]

Cheers Guys,

Curiosity is likely to get the best of me. I'm probably going to have to 
build two webservers & try this out :-)



James Holden wrote:
> On Thu, Sep 20, 2007 at 08:11:46PM +0100, Chris Myers wrote:
>> Hi Guys,
> 
> Hi Chris,
> 
>> Something that was mentioned in the recent Xen talk.
>>
>> He mentioned that he had a number of Xen servers using the same IP 
>> address & that Windows machine were not capable of this. Assuming that I 
>> heard correctly, I have a few questions:
> 
> Yes... fire away.
> 
>> 1. This doesn't appear to be possible. How is this achieved?
> 
> By having only one of them respond to ARP requests at a time, and a
> mechanism to ensure that the privilege is passed over to another machine
> in the event of a failure.
> 
> The machine wearing the hat then distributes requests off to other
> machines.
> 
> IP failover is usually achieved with 'heartbeat'.
> Load balancing is done with LVS.
> Back-end service monitoring is often done with ldirectord.
> 
>> 2. There must be a benefit. What advantage is there for having multiple 
>> machines on one IP address?
> 
> Load balancing and redundancy mainly. Our web stuff at work does this -
> boxes can fail and stuff keeps ticking along.
> 
>> 3. Why can't Windows do this?
> 
> Good question ;-) Ask Bill.
> 
>> I'd love to know. :-)
> 
> It's quite hard to get your head around how it works if you've not seen
> it before. Judging by most of the MCSEs I've met, it'd make their heads
> explode way before they grasped it (/ducks).
> 
> Also.... there are hardware solutions to failover and load balancing
> (that, in my experience, aren't very good). I suspect Windows shops are
> more likely to purchase this sort of thing instead due to the shiny
> factor, presumed ease of use and commercial support, as well as PHB
> management appeal.
> 
> james
> 
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