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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1029) Allow embedding leader election into the RM
Date Tue, 10 Dec 2013 10:55:08 GMT

    [ https://issues.apache.org/jira/browse/YARN-1029?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13844182#comment-13844182

Karthik Kambatla commented on YARN-1029:

Correction: Actually, it would be the AdminService that will have to implement ZKFCProtocol,
not ActiveStandbyElector.

bq. What are the pros and cons of using ZKFC embedded vs ActiveStandbyElector?
Indeed, my first implementation was embedding ZKFC. While it works fine, I found it round
about and has some avoidable overhead. Embedding ActiveStandbyElector definitely seems like
a simpler, cleaner approach.

Cons of ZKFC / Pros of ActiveStandbyElector:
# ZKFC communicates to the RM through RPC; when embedded, both are in the same process.
# In addition to ActiveStandbyElector, ZKFC has other overheads - health monitoring, fencing
etc. which might not be required in a simple embedded option.
# ZKFC#formatZK() needs to be exposed through rmadmin, which complicates it further.
# Embedding ZKFC isn't very clean.

Cons of ActiveStandbyElector: AFAIK, the only drawback of ActiveStandbyElector is having AdminService
implement ZKFCProtocol - two methods: cedeActive() and gracefulFailover(). These methods are
simple and straight-forward and are needed only to be able to safely failover manually when
automatic-failover is enabled. 

> Allow embedding leader election into the RM
> -------------------------------------------
>                 Key: YARN-1029
>                 URL: https://issues.apache.org/jira/browse/YARN-1029
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>            Reporter: Bikas Saha
>            Assignee: Karthik Kambatla
>         Attachments: yarn-1029-approach.patch
> It should be possible to embed common ActiveStandyElector into the RM such that ZooKeeper
based leader election and notification is in-built. In conjunction with a ZK state store,
this configuration will be a simple deployment option.

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