ZooKeeper Observers๏
Observers: Scaling ZooKeeper Without Hurting Write Performance๏
Observers are non-voting members of an ensemble which only hear the results of votes, not the agreement protocol that leads up to them.
Therefore they can fail, or be disconnected from the cluster, without harming the availability of the ZooKeeper service.
How to use Observers๏
Firstly, in the config file of every node that is to be an Observer, you must place this line:
peerType=observer
Secondly, in every server config file, you must add :observer to the server definition line of each Observer. For example:
server.1:localhost:2181:3181:observer
This tells every other server that server.1 is an Observer, and that they should not expect it to vote.
$ bin/zkCli.sh -server localhost:2181
Example use cases๏
As a datacenter bridge
As a link to a message bus
Tips๏
zookeeper-3.4.10-observer/
โโโ conf/
โ โโโ java.env
โ โโโ zoo-2181.cfg
โ โโโ zoo-2182.cfg
โ โโโ zoo-2183.cfg
โ โโโ zoo-2188.cfg
โโโ data-2181/
โ โโโ myid
โโโ data-2182/
โ โโโ myid
โโโ data-2183/
โ โโโ myid
โโโ data-2188/
โ โโโ myid
โโโ logs-2181
โโโ logs-2182
โโโ logs-2183
โโโ logs-2188
cd /usr/local/zookeeper-3.4.10-observer
bin/zkServer.sh start conf/zoo-2181.cfg
bin/zkServer.sh start conf/zoo-2182.cfg
bin/zkServer.sh start conf/zoo-2183.cfg
bin/zkServer.sh start conf/zoo-2188.cfg
bin/zkServer.sh status conf/zoo-2181.cfg
bin/zkServer.sh status conf/zoo-2182.cfg
bin/zkServer.sh status conf/zoo-2183.cfg
bin/zkServer.sh status conf/zoo-2188.cfg
bin/zkCli.sh -server localhost:2188