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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2582) Scope dfs.ha.namenodes config by namespace
Date Tue, 22 Nov 2011 01:24:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13154807#comment-13154807
] 

Todd Lipcon commented on HDFS-2582:
-----------------------------------

Example config under the proposed scheme, for a DN which is part of two federated namespaces,
each of which is HA-enabled:

{code}
dfs.federation.nameservices=namespace1,namespace2
dfs.ha.namenodes.namespace1=ns1-nn1,ns1-nn2
dfs.ha.namenodes.namespace2=ns2-nn1,ns2-nn2
dfs.namenode.http-address.namespace1.ns1-nn1=node1.example.com:50070
{code}

Not entirely clear still: do namenode IDs need to be unique across federated nameservices?
If they do, then why do we need the {{namespace1}} component in the {{dfs.namenode.http-address...}}
config?
                
> Scope dfs.ha.namenodes config by namespace
> ------------------------------------------
>
>                 Key: HDFS-2582
>                 URL: https://issues.apache.org/jira/browse/HDFS-2582
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>
> HDFS-2301 started the process of adding configuration for HA, but one piece is missing.
The current state of the configuration is, I believe:
> {{dfs.ha.namenodes}} - a list of identifiers for HA namenodes
> {{dfs.federation.nameservices}} - a list of federated namespaces
> {{dfs.namenode.rpc-address[.nameservice-id][.namenode-id]}} - some specific config for
the given namenode. If HA or federation is disabled, the extra components can be elided for
backwards compatibility.
> The issue here is that there is no easy way to discern which NN is paired with which
other NN without explicitly. Additionally, adding a new federated namespace to a config will
require changes to {{dfs.ha.namenodes}} which makes templating harder. It would be simpler
to change {{dfs.ha.namenodes}} to be nameservice-scoped: {{dfs.ha.namenodes.<nameservice-id>}}.

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