[ClusterLabs] Trying to understand dampening (ping)

[Andrei Borzenkov]

On 15.10.2021 13:24, Klaus Wenninger wrote:
> On Fri, Oct 15, 2021 at 12:01 PM Andrei Borzenkov <arvidjaar at gmail.com>
> wrote:
> 
>> On Fri, Oct 15, 2021 at 9:25 AM Klaus Wenninger <kwenning at redhat.com>
>> wrote:
>>
>>> Main pain-point here is that ping-RA allows us to configure the count of
>> pings sent, but it
>>> is just using the exit-value from ping that becomes negative already
>> when one of the
>>> answers is missing.
>>
>> Use fping instead? Which is supported by ping RA and should behave
>> exactly as needed - report host alive if at least one reply was
>> received.
>>
> I like fping but it having some reputation as DOS tool not everybody might
> be fine installing it.
> And we will still have something that would be fine with at least a 50%
> packet
> loss, which as well might not be acceptable to qualify a host as reachable.
> But of course we still can tweak it even with the current implementation to
> let's say a loss <20% by giving the same host 5 times and having
> the limit set to 4.
> 
>>
>> Maybe when using ping RA could also parse ping output instead of
>> relying on exit status.
>>
> as the fence-agent referenced is doing ;-)
> 

Actually simply having inner loop from 1 to $OCF_RESKEY_attempts with
"ping -c 1" is more simple and portable. But I am not convinced it is
worth the troubles.