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https://issues.apache.org/jira/browse/HADOOP-8232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242544#comment-13242544
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Steve Loughran commented on HADOOP-8232:
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I'm not sure the best way to automate this; I think isolating the inner code
from the entry point, testing that -including by capturing the output- would be
the best tactic.
Manual testing so far is done with some different configurations
[https://github.com/steveloughran/hadoop-patches/tree/master/misc/topology]
#script based mapper with a script that is not on the path
#a script mapper where the script is echo
#a table mapper with no table defined
#a table mapper with a table that is defined but missing
#a valid table mapper
Tests with hostnames in a file and on the command line were tried; examples
will be shown.
> Provide a command line entry point to view/test topology options
> ----------------------------------------------------------------
>
> 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
> Assignee: Steve Loughran
> Priority: Minor
> Attachments: HADOOP-8232.patch
>
>
> 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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