Vladimir created AURORA-1948:
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Summary: Adding instances leads to constraints conflict
Key: AURORA-1948
URL: https://issues.apache.org/jira/browse/AURORA-1948
Project: Aurora
Issue Type: Bug
Components: Scheduler
Reporter: Vladimir
Priority: Critical
Problem:
When scaling instances (adding more instances) there could be a constraint
conflict.
Example:
Let's say you have a mesos cluster with 3 racks. You want to deploy a service
and create aurora job with the "rack" constraint "limit" set to 1. So basically
it means that no more than 1 instance per rack. The job has number of instances
set to 2, for example. The deployment will succeed and user would get 2
instances running on 2 different racks.
Next user would like to scale it to 4 instances by adding 2 more instances. In
this case if user won't update the rack constraint (set limit to 2 or larger),
the update job would fail showing "Limit not satisfied: rack". If user would
modify the constraints, then the regular Job update would be involved which
would add new instances but also update the existing ones (rolling deploy).
Proposal:
The proposal is to be able to update the constraints while adding new instances
in order to satisfy the limits and be sure that the currently running instances
won't be redeployed.
So in my example, when scaling up we can recalculate the rack limit on our end,
update it's value in the job config, update number of instances and start job
update. Aurora would leave 2 currently running instances as they are and only
add two new instances making sure that the new constraints are satisfied..
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