[jira] [Created] (HDFS-2925) Revert ScriptBasedMapping semantics to the existing ones, add DNS mapping diagnostics in progress

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

Revert ScriptBasedMapping semantics to the existing ones, add DNS mapping diagnostics in progress
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                 Key: HDFS-2925
                 URL: https://issues.apache.org/jira/browse/HDFS-2925
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 0.23.0, 0.24.0
            Reporter: Steve Loughran
            Assignee: Steve Loughran
            Priority: Minor


HADOOP-7878 still doesn't let the block manager switch to non-scripted topologies because the static mapping is still getting it wrong -it should just look at the configuration for a non-null script name, as per the usual {{ScriptBasedMapping}}, so as to keep tests backwards compatible.

In the process, make it possible to debug topologies by
# {{#toString()}} operations to provide summary information, and for the {{CachedDNSToSwitchMapping}}, to include information on the inner mapping. {{ScriptBasedMapping}} to include the script name.
# {{AbstractDNSToSwitchMapping} to offer a method {{getSwitchMap()}} to return a cloned map of the mapping, or null if this is not known.
# {{AbstractDNSToSwitchMapping} to offer a method {{dumpTopology()}} to take this switch map and the toString() and generate a topology dump suitable for humans.
# Implementing the switch map method for the standard mappings (Cached -> cached map, Static -> static map, Script -> null).
These methods are all for debugging, but there is no reason not to use the contents of {{getSwitchMap()}} in service web pages providing details on the service's current view of the network topology, as it may differ from the expectations of the script author.

time: 30m to implement, 1h30 to write more tests and run them.


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