[
https://issues.apache.org/jira/browse/HDFS-2354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13117927#comment-13117927
]
Suresh Srinivas commented on HDFS-2354:
---------------------------------------
bq. Suresh, whatever you told is true when you use Linux HA for determining
Active / Standby roles. Linux HA can easily work with scripts. Going one step
further, one can configure standByToActive script in HA framework & avoid the
usage of HAServiceProtocol interface itself.
And how does the HA framework talk to a server to affect standbyToActive? That
is where HAServiceProtocol comes into play. In standbyToActive script, you run
a command that talks to the namenode to make it active.
bq. I mean to say there are many ways of plumbing a Leader Election Service
with Namenode. We need to consider other Leader Election mechanisms also. An
alternative is Zookeeper based Leader Election Service where the LES and
Namenode may run together in the same JVM.
HDFS-1623 approach was to run FailoverController (or CRM/LRM in linux HA lingo)
separate from the service for which HA is being enabled. The reasons for that
is described in the document, hence HAServiceProtocol.
bq. So the argument boils down to the question whether FailoverController
daemon should be separate from the Namenode. If they are kept separately,
having only the transition related APIs in HAServiceProtocol looks to be better
decision. But when considering the case that both FailoverController daemon &
Namenode runs in the same JVM, it is very much required that start*() & stop()
APIs be supported in the HAServiceProtocol interface.
Even in this case, you could build a FailoverController that runs on the same
JVM, but interacts with Namenode using HAServiceProtocol. The approach from
HDFS-1974 does not preclude you from that.
I have not looked at the patch in detail yet. At a high level, it is adding
things/making changes that I am not in favor of. I will respond in detail about
this.
> Generalize the HAServiceProtocol interface
> ------------------------------------------
>
> Key: HDFS-2354
> URL: https://issues.apache.org/jira/browse/HDFS-2354
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: name-node
> Reporter: Justin Joseph
> Assignee: Justin Joseph
> Attachments: HAService_fw_Class_Diagram.JPG, HDFS-2354.1.patch,
> HDFS-2354.patch
>
>
> This JIRA intends to revisit the patches committed for HADOOP-7455 and
> HDFS-1974 & to provide more generic interfaces which allows alternative HA
> implementations to co-exist complying with HAServiceProtocol.
> Some of the considerations are
> 1) Support life cycle methods (start*() and stop() APIs) in HAServiceProtocol
> 2) Support custom states in HAServiceProtocol
> 3) As per the patch submitted for HDFS-1974, Namenode implements HAService
> interface. This needs to be reconsidered.
> I will elaborate on these points, in the form of comments below.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
