[Pacemaker] Is possible to configure Pacemaker Active / Passive failover without hardware?

[Digimer]

It is possible in the same way that it is possible to drive on the 
highway without your seatbelt. First time something goes wrong though, 
you are in deep trouble. The biggest risk is a node that locks up but 
doesn't die. Any network based "detection" will not be able to tell the 
difference between a locked up node that may recover from a truly dead 
node. The only way to be sure is to fence it.

So practically speaking, no, you must have fencing and the fence 
mechanism must be external to the node to be of use. The most common 
method is using a server's out of band management (IPMI, iLO, DRAC, 
etc). If you don't have this, then the APC brand AP7900 (or your 
country's version of) is an excellent switched PDU that works as a 
fantastic fence device. I frequently see these used for ~$200 (canadian).

The 'fence_pcmk' is meant to hook cman's fencing into pacemaker's. It 
still requires a real fence device be setup in pacemaker.

hth

digimer

On 06/07/2013 10:34 AM, Michael Furman wrote:
> Dear Pacemaker community!
> I want to install 2 Centos machines and to configure HA using one
> virtual IP.
> I do not want to use power card or something like this.
> I want to use communication to determine the failing of nodes: broadcast
> / mulicast UDP / TCP.
>
>
> But I am confused if it possible. From one side I see here that the
> failover is configured without any hardware:
> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-plugin/html-single/Clusters_from_Scratch/index.html#_perform_a_failover
> On the second side I see that on quickstart and FAQ required a fencing
> device (that is hardware):
>
> 1.On quickstart http://clusterlabs.org/quickstart-redhat.html you can
> find the followowing commands: |ccs -f /etc/cluster/cluster.conf
> --addfencedev pcmk agent=fence_pcmk|
>
> |2.|Similar here: http://clusterlabs.org/quickstart-ubuntu.html
> |<fencedevice name="pcmk" agent="fence_pcmk"/>|||
>
> 3.http://clusterlabs.org/faq.html
> Q: Do I need a fencing device?
> A: Yes. Fencing is the only 100% reliable way to ensure the integrity of
> your data and that applications are only active on one host. Although
> Pacemaker is technically able to function without Fencing, there are a
> good reasons SUSE and Red Hat will not support such a configuration.
>
> Please help!
> Will be great if you provide the link to the appropriate documentation.
>
> Best regards,
>
> Michael
>
>
>
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-- 
Digimer
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