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This is an archived version of the documentation downloaded from LogScale Documentation Archives. Up to date documentation, and documentation for later versions, is available on LogScale Documentation

### Switch Kafka and ZooKeeper

Methods for switching Kafka and ZooKeeper configurations in LogScale environments, including setting up new clusters, deleting existing data, or creating new queues and topics. Detailed instructions cover data deletion procedures, queue creation requirements, and the proper restart sequence for Kafka, ZooKeeper, and LogScale nodes to ensure successful cluster transitions.

In the event of issues or the need to change your infrastructure, there are two main ways to switch LogScale to another Kafka cluster:

1. Set up a new Kafka/ZooKeeper cluster and re-configure LogScale to use the new cluster.

2. Reset Kafka and ZooKeeper.

Setting up a new Kafka/ZooKeeper cluster and pointing LogScale to it is the simplest. Resetting Kafka is described in the following section.

### Note

In order to be able to reset Kafka for LogScale you need to first set the variable `ALLOW_KAFKA_RESET_UNTIL_TIMESTAMP_MS`, which is not set by default.

#### How to Reset Kafka/ZooKeeper

There are two ways to reset your Kafka cluster:

1. Delete the Kafka and ZooKeeper data and reuse the cluster

2. Create new Kafka queues/topics with new names in the Kafka Cluster

These are described in the following sections.

##### Delete Kafka and ZooKeeper Data and Re-Use Cluster

You could reset the current Kafka and ZooKeeper cluster by deleting their data directories on the filesystem on each node. This is the same as starting up a new and empty Kafka/ZooKeeper cluster. To do this, delete everything inside Kafka's data directory. Then delete the folder `version-2` inside ZooKeeper's data directory.

It's important that you not delete the ZooKeeper file `myid` in ZooKeeper's data directory. The `myid` is a configuration file that contains the id of the ZooKeeper node in the ZooKeeper cluster and must be there at startup.

After doing this, you will have created completely new ZooKeeper and Kafka clusters.

##### Create New Kafka Queues/Topics with New Names in Kafka Cluster

Instead of resetting Kafka as described previously, you can alternatively let LogScale use a new set of queues in the existing Kafka cluster. When reusing the same Kafka cluster, LogScale must be configured with a new `HUMIO_KAFKA_TOPIC_PREFIX` to detect the changes.

To make this process easier, the `ALLOW_KAFKA_RESET_UNTIL_TIMESTAMP_MS` variable can be used to allow kafka resets until a specific timestamp. This allows a reset of the Kafka configuration, with the default (disabled) setting being enabled when the timestamp is reached. It provides a six hour window for the reset to occur. To use, set the environment variable to a time in the future and then follow the instructions in Switching Kafka to reset the Kafka configuration.

It's important to note that it will not work to delete and recreate topics with the same names. In that case LogScale cannot detect the Kafka switch. If Kafka is managed by LogScale (`KAFKA_MANAGED_BY_HUMIO`), the new topics will be created automatically when LogScale starts up. Otherwise you must create topics externally before you start LogScale.

#### Restarting Kafka, ZooKeeper and LogScale

Now you're ready to get the Kafka/ZooKeeper cluster started. This is typically done by starting the ZooKeeper nodes. Wait for all nodes to be running and verify the ZooKeeper cluster. Then start all Kafka nodes, wait for them to be running and verify the Kafka cluster.

Once Kafka and ZooKeeper have started, start the LogScale nodes. It's important to start one LogScale node first. This node will detect the Kafka switch and create a new epoch in LogScale.

To verify that the Kafka switch was detected and handled, look for this line in the LogScale debug log:

    Switching epoch to=${epochKey} from=${latestEpoch.kafkaClusterId}
    - I'm the first cluster member to get here
      for this kafka. newEpoch=${newEpoch}

When the first node is up and running and the above logline confirms a new epoch has been created, the rest of the LogScale nodes can be started.

At that point, the LogScale cluster should be running again. Check the cluster nodes in the administrative section of the LogScale user interface: `http://$HUMIOHOST/system/administration/partitions/ingest`

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