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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11096) Support rolling upgrade between 2.x and 3.x
Date Thu, 07 Sep 2017 16:36:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16157192#comment-16157192
] 

Allen Wittenauer commented on HDFS-11096:
-----------------------------------------

{code}
set -e
{code}

I'm really not a fan of using set -e unless one absolutely must.  Using it eliminates any
possible use of failure mechanisms, including in if tests. There are a lot of caveats when
it is in play.  

{code}
set -x
{code}

Is this just temporary?

{code} 
for hostname in ${HOSTNAMES[@]}; do
    ssh -i ${ID_FILE} root@${hostname} ". /tmp/env.sh
{code}

It seems there are a few functions like this that have implementations in hadoop-functions.sh.
 Shouldn't this just leverage that code?  [See also HADOOP-14009 .]  The bash settings in
place (see above) will be an issue though.

{code}
  cd ${HADOOP_3}
  sbin/hadoop-daemon.sh start namenode -rollingUpgrade started
{code}

If it's hadoop 3.x, shouldn't this be using non-deprecated commands?

{code}
   sudo apt-get install -y git
{code}

This is kind of an interesting one. If I'm using this code, then I'm either already in a git
repo or I've got a source tarball.  Given that the git hash is encoded at build time, I think
there might be an implicit requirement that git is already installed.  In the case of some
of the other Ubuntu-isms (apt-install of wget), there are likely generic ways to deal with
them. (e.g., use the installed perl/python/java).  If the intent is to just use the docker
images that ship with Hadoop, git is pretty much a requirement for Apache Yetus....

{code}
# Tested on an Ubuntu 16.04 host
{code}

Probably worth mentioning HADOOP-14816 upgrades the Dockerfile to Xenial.

> Support rolling upgrade between 2.x and 3.x
> -------------------------------------------
>
>                 Key: HDFS-11096
>                 URL: https://issues.apache.org/jira/browse/HDFS-11096
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: rolling upgrades
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Andrew Wang
>            Assignee: Sean Mackrory
>            Priority: Blocker
>         Attachments: HDFS-11096.001.patch, HDFS-11096.002.patch
>
>
> trunk has a minimum software version of 3.0.0-alpha1. This means we can't rolling upgrade
between branch-2 and trunk.
> This is a showstopper for large deployments. Unless there are very compelling reasons
to break compatibility, let's restore the ability to rolling upgrade to 3.x releases.



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