[jira] [Commented] (HBASE-9360) Enable 0.94 -> 0.96 replication to minimize upgrade down time

["Jeffrey Zhong (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-9360?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13809858#comment-13809858 ] 

Jeffrey Zhong commented on HBASE-9360:
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I did a prototype @https://github.com/hortonworks/HBaseReplicationBridgeServer and tested replication from a 0.94 cluster to a 0.96 cluster.

The remaining work is to bring the slave cluster to a good base(which we're currently using CopyTable) when setting up replication.  

h6. Support import from a 0.94 export sequence file. 
Currently we PBed org.apache.hadoop.hbase.client.Result so a 0.96 cluster cannot import 0.94 exported files while we can easily add that support. (personal preferred option)

h6. Use snapshot without any code changes:
1) Setup replication without starting replication bridge server so source cluster is queuing WALs
2) Use Snapshot to bring destination cluster to a good base
3) Starts replication bridge servers to drain WALs queued up from step 1

h6. Enable CopyTable against Replication Bridge Server
This option is least desired one because it will involves significant code changes to have a faked root znode, support root table scan, support meta table scan, delete and multi command in replication bridge server.



> Enable 0.94 -> 0.96 replication to minimize upgrade down time
> -------------------------------------------------------------
>
>                 Key: HBASE-9360
>                 URL: https://issues.apache.org/jira/browse/HBASE-9360
>             Project: HBase
>          Issue Type: Brainstorming
>          Components: migration
>    Affects Versions: 0.98.0, 0.96.0
>            Reporter: Jeffrey Zhong
>
> As we know 0.96 is a singularity release, as of today a 0.94 hbase user has to do in-place upgrade: make corresponding client changes, recompile client application code, fully shut down existing 0.94 hbase cluster, deploy 0.96 binary, run upgrade script and then start the upgraded cluster. You can image the down time will be extended if something is wrong in between. 
> To minimize the down time, another possible way is to setup a secondary 0.96 cluster and then setup replication between the existing 0.94 cluster and the new 0.96 slave cluster. Once the 0.96 cluster is synced, a user can switch the traffic to the 0.96 cluster and decommission the old one.
> The ideal steps will be:
> 1) Setup a 0.96 cluster
> 2) Setup replication between a running 0.94 cluster to the newly created 0.96 cluster
> 3) Wait till they're in sync in replication
> 4) Starts duplicated writes to both 0.94 and 0.96 clusters(could stop relocation now)
> 5) Forward read traffic to the slave 0.96 cluster
> 6) After a certain period, stop writes to the original 0.94 cluster if everything is good and completes upgrade
> To get us there, there are two tasks:
> 1) Enable replication from 0.94 -> 0.96
> I've run the idea with [~jdcryans], [~devaraj] and [~ndimiduk]. Currently it seems the best approach is to build a very similar service or on top of https://github.com/NGDATA/hbase-indexer/tree/master/hbase-sep with support three commands replicateLogEntries, multi and delete. Inside the three commands, we just pass down the corresponding requests to the destination 0.96 cluster as a bridge. The reason to support the multi and delete is for CopyTable to copy data from a 0.94 cluster to a 0.96 one.
> The other approach is to provide limited support of 0.94 RPC protocol in 0.96. While an issue on this is that a 0.94 client needs to talk to zookeeper firstly before it can connect to a 0.96 region server. Therefore, we need a faked Zookeeper setup in front of a 0.96 cluster for a 0.94 client to connect. It may also pollute 0.96 code base with 0.94 RPC code.
> 2) To support writes to a 0.96 cluster and a 0.94 at the same time, we need to load both hbase clients into one single JVM using different class loader.
> Let me know if you think this is worth to do and any better approach we could take.
> Thanks!



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