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From Reka Thirunavukkarasu <r...@wso2.com>
Subject Re: Defining min/max in partition context
Date Thu, 21 Nov 2013 07:21:37 GMT
Hi

On Wed, Nov 20, 2013 at 7:05 PM, Lahiru Sandaruwan <lahirus@wso2.com> wrote:

> Hi all,
>
> I and Reka had an offline chat on $subject.
> Currently we have min/max per each partition. We cannot define overall
> minimum as per current design.
>
Scenario to be discussed,
> ____________________
>
> Say we have 3 partitions with min is 2 for each. So the overall min is
> 6(which is not defined explicitly).
> Currently if one partition become unavailable(crashed) we will not spawn
> the 2 instances in other partitions.
>
> Also if the max is 10 for all the partition, we only allow 20 if one
> partition is crashed.
>
> Solution,
> _______
>
> We can keep minimum policy as it is, since it will scale up in other
> partitions if the one partition is unavailable(and load is not tolerable to
> existing instances).
>
> But if one partition is down, i think we need to allow the system to scale
> up to that level.
>
> i.e. in above scenario, we will let the system scale up to 30 instance.
>
> So if the crashed partition came up again, we can spawn minimum count in
> the partition, and let the system become balanced through autoscaling, to
> avoid the spawn/terminate overhead.(it will remove the extra instances if
> the load is low).
>
> Question here might be, how do we find that it become available?
>
I hope that when we bring up the crashed (due to power failure) partition
again, the instances which got spun in the partition will also get rebooted
and they will send the relevant messages. So that Topology will get updated
accordingly. But in case of whole partition got crashed and we have to
bring up a new partition, we have to decide on how to handle it.

In addition to this Autoscaler can check for the no of running instances in
a partition against other partition to check whether a partition is healthy
or not. This is applicable only for Round Robin Algorithm.

Thanks,
Reka

If we try to spawn periodically it will be a huge overhead.
>
> Please send your thoughts over!
>
> Thanks.
>
> --
> --
> Lahiru Sandaruwan
> Software Engineer,
> Platform Technologies,
> WSO2 Inc., http://wso2.com
> lean.enterprise.middleware
>
> email: lahirus@wso2.com cell: (+94) 773 325 954
> blog: http://lahiruwrites.blogspot.com/
> twitter: http://twitter.com/lahirus
> linked-in: http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146
>
>


-- 
Reka Thirunavukkarasu
Software Engineer,
WSO2, Inc.:http://wso2.com,
Mobile: +94776442007

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