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https://issues.apache.org/jira/browse/HADOOP-8193?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Lipcon reopened HADOOP-8193:
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> Refactor FailoverController/HAAdmin code to add an abstract class for
> "target" services
> ---------------------------------------------------------------------------------------
>
> Key: HADOOP-8193
> URL: https://issues.apache.org/jira/browse/HADOOP-8193
> Project: Hadoop Common
> Issue Type: Improvement
> Components: ha
> Affects Versions: 0.23.3, 0.24.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Fix For: 0.23.3, 0.24.0
>
> Attachments: hadoop-8193.txt, hadoop-8193.txt, hadoop-8193.txt
>
>
> In working at HADOOP-8077, HDFS-3084, and HDFS-3072, I ran into various
> difficulties which are an artifact of the current design. A few of these:
> - the service name is "resolved" from the logical name (eg ns1.nn1) to an IP
> address at the outer layer of DFSHAAdmin
> -- this means it's difficult to provide the logical name "ns1.nn1" to fence
> scripts (HDFS-3084)
> -- this means it's difficult to configure fencing method per-namespace (since
> the FailoverController doesn't know what the namespace is) (HADOOP-8077)
> - the configuration for HA HDFS is weirdly split between core-site and
> hdfs-site, even though most users see this as an HDFS feature. For example,
> users expect to configure NN fencing configurations in hdfs-site, and expect
> the keys to have a dfs.* prefix
> - proxies are constructed at the outer layer of the admin commands. This
> means it's impossible for the inner layers (eg FailoverController.failover)
> to re-construct proxies with different timeouts (HDFS-3072)
> The proposed refactor is to add a new interface (tentatively named
> HAServiceTarget) which refers to target for one of the admin commands. An
> instance of this class is responsible for creating proxies, creating fencers,
> mapping back to a logical name, etc. The HDFS implementation of this class
> can then provide different results based on the particular nameservice, can
> use HDFS-specific configuration prefixes, etc. Using this class as the
> argument for fencing methods also makes the API more evolvable in the future,
> since we can add new getters to HAServiceTarget (whereas the current
> InetSocketAddress is quite limiting)
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