Chapter 4. Running a multi-node environment

Running the cluster

1. Create the myid file in /var/lib/zookeeper/. Enter ID 1 for the first ZooKeeper node, 2 for the second ZooKeeper node, and so on.

   su - kafka
   echo "<NodeID>" > /var/lib/zookeeper/myid

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   For example:

   su - kafka
   echo "1" > /var/lib/zookeeper/myid

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2. Edit the ZooKeeper /opt/kafka/config/zookeeper.properties configuration file for the following:

   • Set the option dataDir to /var/lib/zookeeper/.
   • Configure the initLimit and syncLimit options.
   • Configure the reconfigEnabled and standaloneEnabled options.

   • Add a list of all ZooKeeper nodes. The list should include also the current node.

     Example configuration for a node of ZooKeeper cluster with five members

     tickTime=2000
     dataDir=/var/lib/zookeeper/
     initLimit=5
     syncLimit=2
     reconfigEnabled=true
     standaloneEnabled=false
     
     server.1=172.17.0.1:2888:3888:participant;172.17.0.1:2181
     server.2=172.17.0.2:2888:3888:participant;172.17.0.2:2181
     server.3=172.17.0.3:2888:3888:participant;172.17.0.3:2181
     server.4=172.17.0.4:2888:3888:participant;172.17.0.4:2181
     server.5=172.17.0.5:2888:3888:participant;172.17.0.5:2181

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3. Start ZooKeeper with the default configuration file.

   su - kafka
   /opt/kafka/bin/zookeeper-server-start.sh -daemon /opt/kafka/config/zookeeper.properties

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4. Verify that ZooKeeper is running.

   jcmd | grep zookeeper

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   Returns:

   number org.apache.zookeeper.server.quorum.QuorumPeerMain /opt/kafka/config/zookeeper.properties

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5. Repeat this procedure on all the nodes of the cluster.

6. Verify that all nodes are members of the cluster by sending a stat command to each of the nodes using the ncat utility.

   Use ncat stat to check the node status

   echo stat | ncat localhost 2181

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   To use four-letter word commands, like stat, you need to specify 4lw.commands.whitelist=* in zookeeper.properties.

   The output shows that a node is either a leader or follower.

   Example output from the ncat command

   ZooKeeper version: 3.4.13-2d71af4dbe22557fda74f9a9b4309b15a7487f03, built on 06/29/2018 00:39 GMT
   Clients:
    /0:0:0:0:0:0:0:1:59726[0](queued=0,recved=1,sent=0)
   
   Latency min/avg/max: 0/0/0
   Received: 2
   Sent: 1
   Connections: 1
   Outstanding: 0
   Zxid: 0x200000000
   Mode: follower
   Node count: 4

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1. Edit the /opt/kafka/config/server.properties Kafka configuration file as follows:

   • Set the broker.id field to 0 for the first broker, 1 for the second broker, and so on.
   • Configure the details for connecting to ZooKeeper in the zookeeper.connect option.
   • Configure the Kafka listeners.

   • Set the directories where the commit logs should be stored in the logs.dir directory.

     Here we see an example configuration for a Kafka broker:

     broker.id=0
     zookeeper.connect=zoo1.my-domain.com:2181,zoo2.my-domain.com:2181,zoo3.my-domain.com:2181
     listeners=REPLICATION://:9091,PLAINTEXT://:9092
     listener.security.protocol.map=PLAINTEXT:PLAINTEXT,REPLICATION:PLAINTEXT
     inter.broker.listener.name=REPLICATION
     log.dirs=/var/lib/kafka

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     In a typical installation where each Kafka broker is running on identical hardware, only the broker.id configuration property will differ between each broker config.

2. Start the Kafka broker with the default configuration file.

   su - kafka
   /opt/kafka/bin/kafka-server-start.sh -daemon /opt/kafka/config/server.properties

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3. Verify that the Kafka broker is running.

   jcmd | grep Kafka

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   Returns:

   process ID kafka.Kafka /opt/kafka/config/server.properties

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4. Verify that all nodes are members of the Kafka cluster by sending a dump command to one of the ZooKeeper nodes using the ncat utility.

   Use ncat dump to check all Kafka brokers registered in ZooKeeper

   echo dump | ncat zoo1.my-domain.com 2181

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   To use four-letter word commands, like dump, you need to specify 4lw.commands.whitelist=* in zookeeper.properties.

   The output must contain all Kafka brokers you just configured and started.

   Example output from the ncat command for a Kafka cluster with 3 nodes

   SessionTracker dump:
   org.apache.zookeeper.server.quorum.LearnerSessionTracker@28848ab9
   ephemeral nodes dump:
   Sessions with Ephemerals (3):
   0x20000015dd00000:
           /brokers/ids/1
   0x10000015dc70000:
           /controller
           /brokers/ids/0
   0x10000015dc70001:
           /brokers/ids/2

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1. Stop the Kafka broker:

   /opt/kafka/bin/kafka-server-stop.sh

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2. Make any changes to the broker configuration that require a restart after completion.

   For further information, see the following:

   • Configuring Kafka
   • Upgrading Kafka brokers and ZooKeeper

3. Restart the Kafka broker:

   /opt/kafka/bin/kafka-server-start.sh -daemon /opt/kafka/config/server.properties

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4. Check that Kafka is running:

   jcmd | grep kafka

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   Returns:

   process ID kafka.Kafka /opt/kafka/config/server.properties

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5. Verify that all nodes are members of the Kafka cluster by sending a dump command to one of the ZooKeeper nodes using the ncat utility.

   Use ncat dump to check all Kafka brokers registered in ZooKeeper

   echo dump | ncat zoo1.my-domain.com 2181

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   To use four-letter word commands, like dump, you need to specify 4lw.commands.whitelist=* in zookeeper.properties.

   The output must contain the Kafka broker you started.

   Example output from the ncat command for a Kafka cluster with 3 nodes

   SessionTracker dump:
   org.apache.zookeeper.server.quorum.LearnerSessionTracker@28848ab9
   ephemeral nodes dump:
   Sessions with Ephemerals (3):
   0x20000015dd00000:
           /brokers/ids/1
   0x10000015dc70000:
           /controller
           /brokers/ids/0
   0x10000015dc70001:
           /brokers/ids/2

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6. Wait until the broker has zero under-replicated partitions. You can check from the command line or use metrics.

   • Use the kafka-topics.sh command with the --under-replicated-partitions parameter:

     /opt/kafka/bin/kafka-topics.sh --bootstrap-server <bootstrap_address>  --describe --under-replicated-partitions

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     For example:

     /opt/kafka/bin/kafka-topics.sh --bootstrap-server localhost:9092 --describe --under-replicated-partitions

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     The command provides a list of topics with under-replicated partitions in a cluster.

     Topics with under-replicated partitions

     Topic: topic3 Partition: 4 Leader: 2 Replicas: 2,3 Isr: 2
     Topic: topic3 Partition: 5 Leader: 3 Replicas: 1,2 Isr: 1
     Topic: topic1 Partition: 1 Leader: 3 Replicas: 1,3 Isr: 3
     # …

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     Under-replicated partitions are listed if the ISR (in-sync replica) count is less than the number of replicas. If a list is not returned, there are no under-replicated partitions.

   • Use the UnderReplicatedPartitions metric:

     kafka.server:type=ReplicaManager,name=UnderReplicatedPartitions

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     The metric provides a count of partitions where replicas have not caught up. You wait until the count is zero.

     Tip

     Use the Kafka Exporter to create an alert when there are one or more under-replicated partitions for a topic.