Sandy Ryza commented on YARN-752:

bq. If the user has provided racks - just trust that information instead of 
resolving and then checking whether the user has provided the correct 
If we do this, I think it would be good at least to log some sort of warnings 
when the given and expected racks don't match up. The consequences of a user 
getting it wrong can be pretty subtle.

bq.  but isn't it possible for users to ask for specific hosts, without 
specifying racks (Ignoring scheduler implementation here)
Currently, it does not make sense for users to ask for specific hosts without 
specifying racks in any scheduler implementation.  Containers may still be 
scheduled on those nodes, but they will be treated like any other non-local 
nodes for the purposes of delay-scheduling and locality-specific requests. I 
believe that this is not just an implementation issue, but a result of the 
protocol.  A scheduler having zero containers requested on rack1, but non-zero 
containers requested on nodes on rack1, can occur when a single container was 
requested for any of multiple nodes on rack1.

> In AMRMClient, automatically add corresponding rack requests for requested 
> nodes
> --------------------------------------------------------------------------------
>                 Key: YARN-752
>                 URL: https://issues.apache.org/jira/browse/YARN-752
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: api, applications
>    Affects Versions: 2.0.4-alpha
>            Reporter: Sandy Ryza
>            Assignee: Sandy Ryza
>         Attachments: YARN-752-1.patch, YARN-752-1.patch, YARN-752.patch
> A ContainerRequest that includes node-level requests must also include 
> matching rack-level requests for the racks that those nodes are on.  When a 
> node is present without its rack, it makes sense for the client to 
> automatically add the node's rack.

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