Hi,

engine executes power management (fencing) operation using different host in the same cluster/DC as target host reside. It's an oVirt requirement that each host in the same cluster and data center is able to connect to power management deviced of all other hosts in the same cluster/DC.
​

Here's simplified flow for defaults (fence proxy may be selected in the same cluster or DC)

1. Find all existing hosts in the same cluster​ which don't have connection issues (status Up, Maintenance, NonOperational for a reason different than network issues)
2. Select first host in Up (if no host is Up, then pick any other host, if no host found continue with DC in step 5) and try to execute fence operation
3. If fence operation is successful, exit
4. If not, retry 2 times and if still not successful go back to step 2 but exclude already problematic fence proxy
5. Find all existing hosts in the same data center​ which don't have connection issues (status Up, Maintenance, NonOperational for a reason different than network issues)
6. Select first host in Up (if no host is Up, then pick any other host, if no host found then fail and exit) and try to execute fence operation
7. If fence operation is successful, exit
8. If not, retry 2 times and if still not successful go back to step 6 but exclude already problematic fence proxy
9. If still no success, fail

As you see your setup with only 2 hosts is kinda fragile (and not only for fencing operations), you need to assure that 1 hosts is always in perfect condition. If possible I'd recommend you to add at least one other host if possible to make your setup more resistant to failures.

Martin Perina


On Fri, Jan 13, 2017 at 6:10 PM, cmc <iucounu@gmail.com> wrote:
Hi,

Can someone tell me how the engine decides which power management
proxy/proxies to use (using default cluster/dc config)? I am using
drac 7 for a fence agent in my two host cluster, and have noticed that
one of the hosts cannot contact the drac. My guess is that the engine
is using one host to as a power management proxy and hosts cannot
reach their own drac as they are on the same interface + vlan.

Example scenario:

Engine uses host 2 as power management proxy. It can contact host 1’s
drac, but cannot contact its own drac. In the case of host 2 being
unreachable/kdumping etc, would the engine switch to use host 1 as the
proxy to contact host 2’s drac?

Thanks,

Cam

PS: I'd like to use the APC as an additional fencing agent, each host
has two PSUs connected to two different APCs. Is there a guide on how
to specify two ports on two different PDUs to control power on a host?
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