Chris Douglas commented on YARN-5621:

I think I see where the CL proposal was unclear.

It is an alternative to CE changes; container start remains as-is. The proposal 
was scoped only to localizing resources for running containers. The CE is 
agnostic to new/running containers for an application- it may be used by both, 
concurrently. By adding a new command {{LINK}} to its protocol, the NM can 
instruct the {{ContainerLocalizer}} to create a symlink to a resource for a 
running container. Again, these commands could be grouped.

> a case that already exists for containers on the same node requesting the 
> same resource
Do you mean this is an existing implemented functionality or this is an 
existing use-case?

Neither. The case where running containers (c ~1x~, c ~2y~) for different 
applications (a ~1~, a ~2~) request the same resource _R_ exists. Both will 
start {{ContainerLocalizer}} instances, but only one will download the resource 
to the private cache. In the CL proposal, this is the same as rollback, where 
the CL starts, heartbeats, then receives a command to LINK an existing resource 
without downloading anything. By "a case that already exists", I meant it's a 
case the CL proposal handles implicitly.

bq. yeah, I feel it's inefficient to start a localizer process to only create 

No question. But if localizing a new resource takes a few seconds, for services 
that upgrade over minutes/hours, then a few hundred milliseconds is not worth 
adding {{RUN_SCRIPT}} to the CE.

> Support LinuxContainerExecutor to create symlinks for continuously localized 
> resources
> --------------------------------------------------------------------------------------
>                 Key: YARN-5621
>                 URL: https://issues.apache.org/jira/browse/YARN-5621
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>            Reporter: Jian He
>            Assignee: Jian He
>         Attachments: YARN-5621.1.patch, YARN-5621.2.patch, YARN-5621.3.patch, 
> YARN-5621.4.patch, YARN-5621.5.patch
> When new resources are localized, new symlink needs to be created for the 
> localized resource. This is the change for the LinuxContainerExecutor to 
> create the symlinks.

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