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From Rick Mangi <>
Subject Re: schedule task instances spreading them based on a host attribute.
Date Thu, 30 Mar 2017 18:31:13 GMT
Yeah, we have a dozen or so kafka consumer jobs running in our cluster, each having about 40
or so instances.

> On Mar 30, 2017, at 2:06 PM, David McLaughlin <> wrote:
> There is absolutely a need for custom hook points in the scheduler (injecting default
constraints to running tasks for example). I don't think users should be asked to write custom
scheduling algorithms to solve the problems in this thread though. There are also huge downsides
to exposing the internals of scheduling as a part of a plugin API.
> Out of curiosity do your Kafka consumers span multiple jobs? Otherwise host constraints
solve that problem right?
>> On Mar 30, 2017, at 10:34 AM, Rick Mangi <> wrote:
>> I think the complexity is a great rationale for having a pluggable scheduling layer.
Aurora is very flexible and people use it in many different ways. Giving users more flexibility
in how jobs are scheduled seems like it would be a good direction for the project.
>>> On Mar 30, 2017, at 12:16 PM, David McLaughlin <>
>>> I think this is more complicated than multiple scheduling algorithms. The
>>> problem you'll end up having if you try to solve this in the Scheduling
>>> loop is when resources are unavailable because there are preemptible tasks
>>> running in them, rather than hosts being down. Right now the fact that the
>>> task cannot be scheduled is important because it triggers preemption and
>>> will make room. An alternative algorithm that tries at all costs to
>>> schedule the task in the TaskAssigner could decide to place the task in a
>>> non-ideal slot and leave a preemptible task running instead.
>>> It's also important to think of the knock-on effects here when we move to
>>> offer affinity (i.e. the current Dynamic Reservation proposal). If you've
>>> made this non-ideal compromise to get things scheduled - that decision will
>>> basically be permanent until the host you're on goes down. At least with
>>> how things work now, with each scheduling attempt the job has a fresh
>>> chance of being put in an ideal slot.
>>>> On Thu, Mar 30, 2017 at 8:12 AM, Rick Mangi <> wrote:
>>>> Sorry for the late reply, but I wanted to chime in here as wanting to see
>>>> this feature. We run a medium size cluster (around 1000 cores) in EC2 and
>>>> think we could get better usage of the cluster with more control over the
>>>> distribution of job instances. For example it would be nice to limit the
>>>> number of kafka consumers running on the same physical box.
>>>> Best,
>>>> Rick
>>>>> On 2017-03-06 14:44 (-0400), Mauricio Garavaglia <>
>>>>> Hello!>
>>>>> I have a job that have multiple instances (>100) that'd I like to
>>>>> across the hosts in a cluster. Using a constraint such as "limit=host:1">
>>>>> doesn't work quite well, as I have more instances than nodes.>
>>>>> As a workaround I increased the limit value to something like>
>>>>> ceil(instances/nodes). But now the problem happens if a bunch of nodes
>>>> go>
>>>>> down (think a whole rack dies) because the instances will not run until>
>>>>> them are back, even though we may have spare capacity on the rest of
>>>>> hosts that we'd like to use. In that scenario, the job availability may
>>>> be>
>>>>> affected because it's running with fewer instances than expected. On
>>>>> smaller scale, the former approach would also apply if you want to
>>>> spread>
>>>>> tasks in racks or availability zones. I'd like to have one instance of
>>>>> job per rack (failure domain) but in the case of it going down, the>
>>>>> instance can be spawn on a different rack.>
>>>>> I thought we could have a scheduling constraint to "spread" instances>
>>>>> across a particular host attribute; instead of vetoing an offer right
>>>> away>
>>>>> we check where the other instances of a task are running, looking for
>>>>> particular attribute of the host. We try to maximize the different
>>>> values>
>>>>> of a particular attribute (rack, hostname, etc) on the task instances>
>>>>> assignment.>
>>>>> what do you think? did something like this came up in the past? is it>
>>>>> feasible?>
>>>>> Mauricio>

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