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https://issues.apache.org/jira/browse/HDFS-12990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16325458#comment-16325458
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Chris Douglas commented on HDFS-12990:
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We wrote the compatibility guidelines _to avoid breaking users_. If there was
any benefit to this change, then we could discuss tradeoffs, but there are
none. By retaining this change, we choose to add a bunch of tedious, rote
repairs to sites trying to upgrade from 2.x. It's not challenging to work
around this, but it's annoying and avoidable.
bq. Maybe we should look at NN RPC port as a new feature to ensure the down
stream projects really tested with Hadoop 3 instead of gambling on
compatibility.
That's a creative way to look at it, but changing the NN port doesn't achieve
that in any meaningful sense. Even if this does require changes, they are
superficial. More to the point, we have *no* interest in second-guessing other
projects' testing practices, or challenging whether they "really certified with
Hadoop 3". That's not merely outside our charter, it is antithetical to it.
bq. This is greatest challenge to Hadoop policy.
bq. I know that forever compatibility is not sustainable and it only cost more
in the long run. We should move on and do something better for Hadoop.
Are we looking at the same JIRA? This is not like moving to YARN, which
required a lot of work to shake out its incompatible changes, but we won a
better architecture by it. This upends a 10+ year convention, the project and
its users gain _nothing_ by it, and it is trivial to fix.
> Change default NameNode RPC port back to 8020
> ---------------------------------------------
>
> Key: HDFS-12990
> URL: https://issues.apache.org/jira/browse/HDFS-12990
> Project: Hadoop HDFS
> Issue Type: Task
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Xiao Chen
> Assignee: Xiao Chen
> Priority: Critical
> Attachments: HDFS-12990.01.patch
>
>
> In HDFS-9427 (HDFS should not default to ephemeral ports), we changed all
> default ports to ephemeral ports, which is very appreciated by admin. As part
> of that change, we also modified the NN RPC port from the famous 8020 to
> 9820, to be closer to other ports changed there.
> With more integration going on, it appears that all the other ephemeral port
> changes are fine, but the NN RPC port change is painful for downstream on
> migrating to Hadoop 3. Some examples include:
> # Hive table locations pointing to hdfs://nn:port/dir
> # Downstream minicluster unit tests that assumed 8020
> # Oozie workflows / downstream scripts that used 8020
> This isn't a problem for HA URLs, since that does not include the port
> number. But considering the downstream impact, instead of requiring all of
> them change their stuff, it would be a way better experience to leave the NN
> port unchanged. This will benefit Hadoop 3 adoption and ease unnecessary
> upgrade burdens.
> It is of course incompatible, but giving 3.0.0 is just out, IMO it worths to
> switch the port back.
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