Hi everyone,

I've changed the ntask component to use Hazelcast for the coordination /
group communication activities. This is because, the earlier ZooKeeper
based coordination component use was too much troublesome, where it takes a
whole different ZooKeeper cluster to be set up to properly cluster a Carbon
server which has scheduled tasks. And also, ZooKeeper has little support
for proper error handling, and it's hard/not-possible to prevent some edge
cases.

So with the Hazelcast integration, you will not have to install a different
server, since it just works in a peer to peer fashion inside the Carbon
server itself. And also since it's also used in Axis2 clustering, the
integration is seamless.

The scheduled tasks has three main modes it can work, STANDALONE, CLUSTERED
and REMOTE. I've introduced a new setting called "AUTO", that is being set
in tasks-config.xml, as the default, where, it automatically checks if
clustering is enabled in the system, and switches to CLUSTERED mode if so,
or it falls back to the STANDALONE mode. So in the typical setup, there no
additional settings needs to be changed for distributed tasks to work
properly (other than, startup task server count, which is set to 2 by
default).

With this change, I've removed the coordination (ZK based) components from
products which uses it for ntask. The following products are the changes I
did in branch/trunk and built the possible ones.

DSS - Branch/Trunk
AS:- Branch/Trunk, cannot build branch because of a Jaggary version problem
ELB:- Trunk, coordination-server also removed
GREG:- Branch/Trunk, cannot build branch - Jaggary version problem
Manager:- Trunk
AppFactory:- Trunk
BAM:- Trunk
BPS:- Trunk

SS also uses the coordination-core feature, which they seem to use for
other purposes, not for scheduled tasks. I'd recommend, if possible, to
re-write that part of the code to use Hazelcast instead.

Cheers,
Anjana.

-- 
*Anjana Fernando*
Technical Lead
WSO2 Inc. | http://wso2.com
lean . enterprise . middleware
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