If you haven't already done this when you installed Kafka, you can upgrade the system with apt-get like so:

$ apt-get update
$ apt-get upgrade

Next, create a non-administrative user named, zookeeper to run Kafka. You can do this by executing the following from the command-line:

$ adduser zookeeper --shell=/bin/false --no-create-home --system --group

You should add this user to the DenyUsers section of your nodes /etc/ssh/sshd_config file to prevent it from being able to ssh or sftp into the node. Remember to restart the sshd daemon after making the change. Once the system has finished updating and the user has been created, you can install ZooKeeper.

Navigate to opt directory and download a of ZooKeeper. The official release site is Apache ZooKeeper Releases.

$ cd /opt
$ wget https://archive.apache.org/dist/zookeeper/zookeeper-3.7.1/apache-zookeeper-3.7.1-bin.tar.gz

After the file downloads, untar the ZooKeeper file and create a symbolic to /opt/zookeeper like so:

$ tar -zxf apache-zookeeper-x.x.x-bin.tar.gz
$ ln -s /opt/apache-zookeeper-x.x.x-bin /opt/zookeeper

Navigate to zookeeper sub-directory and create a data directory for ZooKeeper:

$ cd /opt/zookeeper
$ mkdir -p /kafka/zookeeper

Using a text editor, create the ZooKeeper configuration file in the conf sub-directory. Name the file, zoo.cfg. For example, /opt/zookeeper/conf/zoo.cfg. Copy the lines below into that file:

tickTime = 2000
dataDir = /kafka/zookeeper
clientPort = 2181
initLimit = 5
syncLimit = 2
maxClientCnxns=60
autopurge.purgeInterval=1
admin.enableServer=false
4lw.commands.whitelist=*
server.1=127.0.0.1:2888:3888
admin.enableServer=false

Create a myid file in the data sub-directory with just the number 1 as its contents. They you can start ZooKeeper to verify that the configuration is working:

$ bash -c 'echo 1 > /var/zookeeper/data/myid'
$ ./bin/zkServer.sh start

ZooKeeper JMX enabled by default
Using config: /opt/zookeeper-x.x.x/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED

You can also verify that ZooKeeper is running by logging in through the command line interface like so:

$ ./bin/zkCli.sh
Connecting to localhost:2181
2019-06-20 20:56:52,767 [myid:] - INFO [main:Environment@100] - Client
...
2019-06-20 20:56:52,822 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1299] - Session establishment complete on server localhost/127.0.0.1:2181, sessionid = 0x10000f560b50000, negotiated timeout = 30000
WATCHER::
WatchedEvent state:SyncConnected type:None path:null
[zk: localhost:2181(CONNECTED) 0]

The results you see should look something like the above. To exit, hit Ctrl+C once the status is reported as connected.

Stop ZooKeeper and change the ownership of the zookeeper directory like so, adjusting for the version number you installed:

$ ./bin/zkServer.sh stop
$ chown -R zookeeper:zookeeper /opt/zookeeper-x.x.x
$ chown -R zookeeper:zookeeper /var/zookeeper/data

So that ZooKeeper will start when the server is rebooted, you'll need to create a ZooKeeper service file named zookeeper.service in the /etc/systemd/system/ sub-directory. Use a text editor to create the file and copy the following lines into it.

[Unit]
Description=ZooKeeper Daemon
Documentation=http://zookeeper.apache.org
Requires=network.target
After=network.target

[Service]
Type=forking
WorkingDirectory=/opt/zookeeper
User=zookeeper
Group=zookeeper
ExecStart=/opt/zookeeper/bin/zkServer.sh start /opt/zookeeper/conf/zoo.cfg
ExecStop=/opt/zookeeper/bin/zkServer.sh stop /opt/zookeeper/conf/zoo.cfg
ExecReload=/opt/zookeeper/bin/zkServer.sh restart /opt/zookeeper/conf/zoo.cfg
TimeoutSec=30
Restart=on-failure

[Install]
WantedBy=default.target

Start the ZooKeeper service. Enter the first line below to start it. When it finishes, enter the second line to check that it's running and there are no errors reported:

$ systemctl start zookeeper
$ systemctl status zookeeper

$ systemctl enable zookeeper