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https://issues.apache.org/jira/browse/YARN-752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13678470#comment-13678470
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Bikas Saha commented on YARN-752:
---------------------------------

The user needs to only specify a node (and may end up getting a container on 
that node, on that node's rack or somewhere else. There is no need to specify 
the rack of a node explicitly but users may do so. If a user wants any node in 
a set of racks then they should simply directly specify those racks.

This code is not quite correct. If nodes n1, n2, n3 (all in rack1) are present 
then this will end up calling addResourceRequest 3 times for rack1. Should 
probably create a local set of racks, initialized by CR.racks, add nodes' racks 
to the set. Then call addResourceRequest for the rack set.
{code}
+        String rack = RackResolver.resolve(host).getNetworkLocation();
+        if (rack == null) {
+          LOG.warn("Failed to resolve rack for host " + host + ".");
+        } else if (req.racks == null || !req.racks.contains(rack)) {
+          addResourceRequest(req.priority, rack, req.capability,
+              req.containerCount, req);
+        }
{code}

The test needs to improve to catch the above case. Also, should check container 
count for the asks to ensure that counts are correct (with or without user 
specifying the racks). The test is also calling api's without calling start(). 
It works now, but will probably break later once we enforce the life cycle 
inside the client. Things like rack resolution etc probably depend on topoplogy 
information coming from the RM upon registration.
                
> 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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