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From "Eli Collins (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-8209) Add option to enable DN and TT rolling upgrades in branch-1
Date Sun, 25 Mar 2012 22:18:28 GMT
Add option to enable DN and TT rolling upgrades in branch-1

                 Key: HADOOP-8209
                 URL: https://issues.apache.org/jira/browse/HADOOP-8209
             Project: Hadoop Common
          Issue Type: Improvement
    Affects Versions: 1.0.0
            Reporter: Eli Collins
            Assignee: Eli Collins

In 1.x DNs currently refuse to connect to NNs if their build *revision* (ie svn revision)
do not match. TTs refuse to connect to JTs if their build *version* (version, revision, user,
and source checksum) do not match.

This prevents rolling upgrades, which is intentional, see the discussion in HADOOP-5203. The
primary motivation in that jira was (1) it's difficult to guarantee every build on a large
cluster got deployed correctly, builds don't get rolled back to old versions by accident etc,
and (2) mixed versions can lead to execution problems that are hard to debug.

However there are also cases when users know they two builds are compatible, eg when deploying
a new build which contains the same contents as the previous one, plus a critical security
patch that does not affect compatibility. Currently deploying a 1 line patch requires taking
down the entire cluster (or trying to work around the issue by lying about the build revision
or checksum, yuck). These users would like to be able to perform a rolling upgrade.

In order to support this, let's add an option that is off by default, but, when enabled, makes
the DN and TT version check just check for an exact version match (eg "1.0.2") but ignore
the build revision (DN) and the source checksum (TT). Two builds still need to match the major,
minor, and point numbers, but nothing else.

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