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Date: Thu, 20 Dec 2012 10:37:13 +0000 (UTC)
From: "Tom White (JIRA)" <jira@apache.org>
To: yarn-issues@hadoop.apache.org
Message-ID: <JIRA.12607315.1347472391035.36053.1355999833943@arcas>
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Subject: [jira] [Commented] (YARN-103) Add a yarn AM - RM client module
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    [ https://issues.apache.org/jira/browse/YARN-103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13536929#comment-13536929 ] 

Tom White commented on YARN-103:
--------------------------------

> The interface shouldn't really be implemented by anyone outside of YARN

This is the heart of the problem. We don't have a way to say (via the audience annotations) that an interface is for read-only use only - and not for users to implement. An interface may be @Public @Stable from the point of view of a user who wants to call it, but that doesn't mean that folks should implement it themselves, since for interfaces like the one we are discussing we might want to add a new method, say (note that such a change is compatible with @Stable). Adding a new method is fine for the first type of user, but not for the second, since their implementation breaks.

In this case, I think it's likely we'll add more methods. For example, it would be useful to add a waitForState method to YarnClient (which is also an interface), which waits for a given application to reach a particular YarnApplicationState. If YarnClient were a class then this would be a compatible change, but if it's an interface then it is not.

I think we should do one of the following:
1. Change YarnClient and AMRMClient to be concrete implementations.
2. Leave the interface/implementation distinction and make the interfaces @Public @Unstable.

I prefer 1. since these classes are helper classes - they are not a tightly-defined interface.
                
> Add a yarn AM - RM client module
> --------------------------------
>
>                 Key: YARN-103
>                 URL: https://issues.apache.org/jira/browse/YARN-103
>             Project: Hadoop YARN
>          Issue Type: Improvement
>            Reporter: Bikas Saha
>            Assignee: Bikas Saha
>         Attachments: YARN-103.1.patch, YARN-103.2.patch, YARN-103.3.patch, YARN-103.4.patch, YARN-103.4.wrapper.patch, YARN-103.5.patch, YARN-103.6.patch, YARN-103.7.patch
>
>
> Add a basic client wrapper library to the AM RM protocol in order to prevent proliferation of code being duplicated everywhere. Provide helper functions to perform reverse mapping of container requests to RM allocation resource request table format.

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