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From Martin Gainty <mgai...@hotmail.com>
Subject Re: Observers: a link to message bus?
Date Wed, 17 Jan 2018 13:57:29 GMT

From: Bruno Freudensprung <bfreudensprung@expertsystem.com>
Sent: Tuesday, January 16, 2018 7:54 AM
To: user@zookeeper.apache.org
Subject: Observers: a link to message bus?


I have a question regarding this part of the Observers Guide (https://zookeeper.apache.org/doc/r3.4.11/zookeeperObservers.html):
ZooKeeper Observers<https://zookeeper.apache.org/doc/r3.4.11/zookeeperObservers.html>
Setting up a ZooKeeper ensemble that uses Observers is very simple, and requires just two
changes to your config files. Firstly, in the config file of every node ...

"As a link to a message bus : [...] Observers would give a natural integration point for this
work: a plug-in mechanism could be used to attach the stream of proposals an Observer sees
to a publish-subscribe system"

I've not been able to find such a plug-in mechanism in the source code of ZooKeeper. For the
moment the only integration point I can think of is the commitRequest method of the  org.apache.zookeeper.server.quorum.ObserverZooKeeperServer
class. Am I looking in the right direction?

To be honest: this is for the moment only pure curiosity since Apache Kafka seems to be a
more "natural" and out-of-the-box option for an ordered message bus. However since I might
probably need ZooKeeper for its distributed lock and leader election features, I was wondering
if I could use it as an ordered message bus as well.
MG>if ActiveMQ does indeed support ordered messaging for multiple active consumers thru
Message Groups as stated:
MG>Message Groups which is the way to load balance multiple active consumers listening
to the same queue while preserving message order.
MG>i have asked why does Zookeeper not support MessageOrderingTechnology such as ActiveMQ
 as a plugin?
MG>have you discovered "plugin integration" within the Zookeeper Architecture?

Best regards,

MG>Thanks Bruno

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