[Linux-HA] master slave colocation question

[Andrew Beekhof]

On Nov 13, 2007, at 11:52 AM, Cousin Marc wrote:

>>>
>>> So I get it even less :)
>>>
>>>
>>> Doesn't it mean that we would just tell heartbeat that we want to
>>> start
>>> applisr0 anywhere where cloner0 is started ?
>>
>> yes, that's what
>>
>> <rsc_colocation id="r0_et_applis_stopped" from="applisr0"  
>> to="cloner0"
>> to_role="stopped" score="-INFINITY"/>
>>
>> does too.
>>
>> so i assumed thats what you wanted.
>>
>>> I want it to applisr0 run anywhere where cloner0 is master.
>>
>> then you only need the second one
>>
>> <rsc_colocation id="r0_et_applis_master" from="applisr0" to="cloner0"
>> to_role="master" score="+INFINITY"/>'
>>
>>> The idea behind what I was doing was that I would put -INFINITY
>>> anywhere I
>>> wouldn't want applisr0 to run (stopped and slave), and a small score
>>> (something like 100) where I would rather have it to run (my
>>> preferred node
>>> for applisr0).
>>
>> sure, in theory that should also work (though you've demonstrated  
>> that
>> it doesn't and i need to fix that)
>>
>>> If I put +INFINITY as a score for colocation, wouldn't hearbeat
>>> consider that
>>> as long as cloner0 and applisr0 are at the same place, the score is
>>> +INFINITY, wherever it can make both of them run ?
>>
>> no, your +100 preference would still take effect... it would  
>> determine
>> which clone instance we decided to colocate it with
>
> This part is completely obscure to me. I thought +INFINITY + 100  
> would still
> be +INFINITY :)

first +100 is applied
then a clone instance is chosen (this choice take into account the  
+100 preference)
then +INFINITY takes effect

so yes, in the end you end up with +INFINITY either way.
but along the way, the +100 preference will have the desired effect

> Is there somewhere a documentation explaining how all constraints  
> are taken
> into account to determine the final state ? Most of the time, the  
> result is
> OK, but I cannot determine accurately what will happen. I couldn't  
> find
> anything about it in the wiki (maybe I didn't search in the right  
> place).
> BTW, I've created the bug report

There are two related documents at:
    http://oss.beekhof.net/~beekhof/heartbeat/docs/