[jira] [Created] (HADOOP-8232) Provide a command line entry point to view/test topology options

["Steve Loughran (Created) (JIRA)" <ji...@apache.org>]

Provide a command line entry point to view/test topology options
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                 Key: HADOOP-8232
                 URL: https://issues.apache.org/jira/browse/HADOOP-8232
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: util
    Affects Versions: 0.23.1
            Reporter: Steve Loughran
            Priority: Minor


Add a new command line entry point "topo" with commands for preflight checking of a clusters topology setup. 

The initial operations would be to list the implementation class of the mapper, and attempt to load it, resolve a set of supplied hostnames, then dump the topology map after the resolution process.

Target audience: 
# ops teams trying to get a new/changed script working before deploying it on a cluster.
# someone trying to write their first script.

Resolve and list the rack mappings of the given host
{code}
hadoop topo test [host1] [host2] ... 
{code}

This would load the hostnames from a given file, resolve all of them and list the results:
{code}
hadoop topo testfile filename
{code}

 This version is intended for the ops team who have a list of hostnames, IP addresses. 

* Rather than just list them, the ops team may want to mandate that there were no /default-rack mappings found, as that is invariably a sign that the script isn't handling a hostname properly.
* No attempt to be clever and do IP address resolution, FQDN to hostname mapping, etc.




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