[ClusterLabs] 2 node clusters - ipmi fencing

[Ondrej]

Hello Ricardo,

On 2/21/20 9:59 AM, Dan Swartzendruber wrote:
> I believe you in fact want each fence agent to run on the other node, yes.
> 
> On February 20, 2020, at 6:23 PM, Ricardo Esteves <mvrk at sapo.pt> wrote:
> 
> Hi,
> 
> I have a question regarding fencing, i have 2 physical servers: node01,
> node02, each one has an ipmi card
> 
> so i create 2 fence devices:
> 
> fence_ipmi_node01 (with ip of ipmi card of server node01) - with
> constraint to prefer to run on node01
> fence_ipmi_node02 (with ip of ipmi card of server node02) - with
> constraint to prefer to run on node02 - configured also a 20s delay on
> this one

with 20s delay: make sure to test that this behaves well with your 
cluster. This value heavily depends on the hardware (IPMI device 
responsiveness) so proper testing is essential.

> Is this the best practice?
> Like this node01 can only fence itself right? and node02 also can only
> fence itself right?
Not exactly:
- node2 will use node1 IPMI device to fence node1
- node1 will use node2 IPMI device to fence node2
Both above should happen regardless of constraints.
Node should never "fence itself" with IPMI device because fencing is 
typically following procedure:
- 1. check state
- 2. turn off
- 3. check state
- 4. turn on
If the node would "fence itself" then there would be no one to continue 
after step 2. :) All actions during fencing with fence_ipmilan or 
similar are taking place on one node. (agents that have unfencing like 
fence_scsi are a different story)

> Shouldn't i configure fence_ipmi_node01 location constraint to be placed
> on node02 and fence_ipmi_node02 location constraint to be placed on
> node01 ? So that node01 can fence node02 and vice versa?
IPMI device of node1 prefering node2 and IPMI device of node2 prefering 
the node1 might be considered a good practice. Important to understand 
is that you configure where the cluster will run 'monitor' check of IPMI 
device. That means you will be monitoring readiness of node1 to use 
node2 IPMI device and readiness of node2 to use node1 IPMI device.

--
Ondrej Famera