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From "Gera Shegalov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1996) Provide alternative policies for UNHEALTHY nodes.
Date Tue, 29 Apr 2014 19:04:17 GMT

    [ https://issues.apache.org/jira/browse/YARN-1996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13984664#comment-13984664

Gera Shegalov commented on YARN-1996:

[~stevel@apache.org]  thanks for pointing out the JIRA about decommissioning. I'll link them
to this JIRA. The main point of this JIRA is to gracefully deal with the UNHEALTHY state determined
by the health script. 

> Provide alternative policies for UNHEALTHY nodes.
> -------------------------------------------------
>                 Key: YARN-1996
>                 URL: https://issues.apache.org/jira/browse/YARN-1996
>             Project: Hadoop YARN
>          Issue Type: New Feature
>          Components: nodemanager, scheduler
>    Affects Versions: 2.4.0
>            Reporter: Gera Shegalov
>            Assignee: Gera Shegalov
>         Attachments: YARN-1996.v01.patch
> Currently, UNHEALTHY nodes can significantly prolong execution of large expensive jobs
as demonstrated by MAPREDUCE-5817, and downgrade the cluster health even further due to [positive
feedback|http://en.wikipedia.org/wiki/Positive_feedback]. A container set that might have
deemed the node unhealthy in the first place starts spreading across the cluster because the
current node is declared unusable and all its containers are killed and rescheduled on different
> To mitigate this, we experiment with a patch that allows containers already running on
a node turning UNHEALTHY to complete (drain) whereas no new container can be assigned to it
until it turns healthy again.
> This mechanism can also be used for graceful decommissioning of NM. To this end, we have
to write a health script  such that it can deterministically report UNHEALTHY. For example
> {code}
> if [ -e $1 ] ; then                                                                
>   echo ERROR Node decommmissioning via health script hack                          
> fi 
> {code}
> In the current version patch, the behavior is controlled by a boolean property {{yarn.nodemanager.unheathy.drain.containers}}.
More versatile policies are possible in the future work. Currently, the health state of a
node is binary determined based on the disk checker and the health script ERROR outputs. However,
we can as well interpret health script output similar to java logging levels (one of which
is ERROR) such as WARN, FATAL. Each level can then be treated differently. E.g.,
> - FATAL:  unusable like today 
> - ERROR: drain
> - WARN: halve the node capacity.
> complimented with some equivalence rules such as 3 WARN messages == ERROR,  2*ERROR ==
FATAL, etc. 

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