Shane Kumpf commented on YARN-7935:

Thanks for the patch [~suma.shivaprasad]! 
{quote}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
I had overlooked this comment previously. There was some discussion on which is 
the appropriate hostname to use in YARN-7797. Ultimately, it's a trade off. We 
had decided there was value in honoring the container_id based hostname, even 
in "host" networking mode, for validating Registry DNS, but it seems that 
decision may be incompatible with the need here. Given "host" networking mode 
is really most appropriate for testing, I guess I don't have a problem with 
changing the behavior to use the NM hostname. /cc [~billie.rinaldi] 

> 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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