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From "Suma Shivaprasad (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-7935) Expose container's hostname to applications running within the docker container
Date Fri, 02 Mar 2018 05:50:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-7935?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16383204#comment-16383204
] 

Suma Shivaprasad commented on YARN-7935:
----------------------------------------

Thanks [~leftnoteasy] for the review. Answers below

1)  This patch introduces a new env CONTAINER_HOSTNAME which is se by NM in prepareContainer. Even
if an AM sets this, it will be overridden by NM in the environment.

2) ContainerLaunch writes out the launch env immediately after calling prepareContainer. 
User specified hostname in

YARN_CONTAINER_RUNTIME_DOCKER_CONTAINER_HOSTNAME

is given precedence as per earlier code flow and there is no change in this behaviour in the
current patch .

However there is change in --hostName behaviour in "host" mode. Earlier the --hostName was
being set to YARN defined hostname(generated from container_id) which is incorrect in host
network mode. In this patch, it is set to the NM's host name which is the correct host name.
Although docker seems to be ignoring the --hostName set in "host" Mode in linux and promotes
the /etc/hosts file from the host, this is not the case in docker on Mac where it is honoring
the value passed in --hostName

> Expose container's hostname to applications running within the docker container
> -------------------------------------------------------------------------------
>
>                 Key: YARN-7935
>                 URL: https://issues.apache.org/jira/browse/YARN-7935
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: yarn
>            Reporter: Suma Shivaprasad
>            Assignee: Suma Shivaprasad
>            Priority: Major
>         Attachments: YARN-7935.1.patch, YARN-7935.2.patch, YARN-7935.3.patch
>
>
> Some applications have a need to bind to the container's hostname (like Spark) which
is different from the NodeManager's hostname(NM_HOST which is available as an env during container
launch) when launched through Docker runtime. The container's hostname can be exposed to
applications via an env CONTAINER_HOSTNAME. Another potential candidate is the container's
IP but this can be addressed in a separate jira.



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