George Kuzhanthai Raj S created AMBARI-24748:
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Summary: Option to configure Zookeeper Observers via Ambari
Key: AMBARI-24748
URL: https://issues.apache.org/jira/browse/AMBARI-24748
Project: Ambari
Issue Type: New Feature
Components: ambari-server
Environment: Operating System: RHEL-7 (64-Bit)
Stack Version: 2.6.4
Ambari Version: 2.6.1
Reporter: George Kuzhanthai Raj S
Feature use :
Zookeeper Observers are non-voting members of an ensemble which only hear the
results of votes, not the agreement protocol that leads up to them.
When zookeeper usage increases (ex: heavy Kafka or HBase usage ), we can
leverage Observers to “sanctify” / isolate the Quorum and front client
connection using Observers.
Issue with current implementation :
The current handling of zookeeper configuration in Ambari essentially prevents
the use of the features.
As is, Observers cannot properly configured using Ambari. While we setup using
manual configurations to enable Observers, they are however overwritten by
Ambari at every service restart.
Explanation :
As per, https://zookeeper.apache.org/doc/r3.4.6/zookeeperObservers.html,
Observers require 2 changes in the zookeeper config file(zoo.cfg).
Every node acting as an Observer, must include the following property:
peerType=observer
Secondly, all nodes of the ensemble acting as an observer must have “:observer”
appended to the server definition line of members.
For example:
server.1=host1.example.com:2888:3888
server.2=host2.example.com:2888:3888
server.3=host3.example.com:2888:3888
server.4=host4.example.com:2888:3888:observer
This tells every member of the ensemble that server.4 is an Observer.
>From Ambari’s perspective :
The first configuration « peerType = observer » can be easily handled using a
specific Ambari configuration group that includes an extra entry in the “custom
zoo.cfg” tab of configurations
The second configuration is more problematic :
The server list is automatically generated by ambari using the list of node for
which a zookeeper service has been installed.
=> It cannot be modified manually.
To get around that we have tried to override the property “server.4” by
including it in the “custom zoo.cfg” tab.
=> this essentially created a second line of the server4 property with the
correct property ( dirty but… )
For example :
server.4=host4.example.com:2888:3888:observer
…
server.1=host1.example.com:2888:3888
server.2=host2.example.com:2888:3888
server.3=host3.example.com:2888:3888
server.4=host4.example.com:2888:3888
Note that custom configuration seem to be systematically placed at the
beginning of the file.
Unfortunately only the last version of the property is actually retained. Ie.
In the above example “server.4=host4.example.com:2888:3888:observer” is
ignored, making it impossible to properly set configurations for the ensemble
Request :
The target would be to make Observers a specific feature of Ambari Zookeeper
configurations.
As a workaround, would it be possible to modify the way Ambari generates the
list of servers in zoo.cfg ?
Here are a few ideas :
Option 1 : Replace automatically generated property and only retain value
defined in the custom property tab
Option 2 : Systematically place custom properties at the bottom of the file
Option 3 : Comment the automatically generated property when a custom property
of a different value exists ?
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