How to manage units

Unit management guide for scaling and running admin utility scripts.

Replication and scaling

Increasing the number of Kafka brokers can be achieved by adding more units to the Charmed Kafka K8s application:

juju add-unit kafka-k8s -n <num_brokers_to_add>

For more information on how to manage units, please refer to the Juju documentation

It is important to note that when adding more units, the Kafka cluster will not automatically rebalance existing topics and partitions. New storage and new brokers will be used only when new topics and new partitions are created.

Partition reassignment can still be done manually by the admin user by using the /opt/kafka/bin/kafka-reassign-partitions.sh Kafka bin utility script. Please refer to the Apache Kafka documentation for more information on the script usage.

IMPORTANT Scaling down is currently not supported in the charm automation.
If partition reassignment is not manually performed before scaling down in order to make sure the decommissioned units do not hold any data, your cluster may suffer to data loss.

Running Kafka Admin utility scripts

Apache Kafka ships with bin/*.sh commands to do various administrative tasks such as:

• bin/kafka-config.sh to update cluster configuration
• bin/kafka-topics.sh for topic management
• bin/kafka-acls.sh for management of ACLs of Kafka users

Please refer to the upstream Kafka project or its documentation, for a full list of the bash commands available in Kafka distributions. Also, you can use --help argument for printing a short summary of the argument for a given bash command.

These scripts can be found in the /opt/kafka/bin folder of the workload container.

IMPORTANT Before running bash scripts, make sure that some listeners have been correctly opened by creating appropriate integrations. Please refer to this table for more information about how listeners are opened based on integrations. To simply open a SASL/SCRAM listener, just integrate a client application using the data-integrator, as described here.

To run most of the scripts, you need to provide:

1. the Kafka service endpoints, generally referred to as bootstrap servers
2. authentication information

Juju admins of the Kafka deployment

For Juju admins of the Kafka deployment, the bootstrap servers information can be obtained using the get-admin-credentials action output:

BOOTSTRAP_SERVERS=$(juju run kafka-k8s/leader get-admin-credentials | grep "bootstrap.servers" | cut -d "=" -f 2)

Admin client authentication information is stored in the /etc/kafka/client.properties file present on every Kafka container. The content of the file can be accessed using juju ssh command:

juju ssh --container kafka kafka-k8s/leader 'cat /etc/kafka/client.properties'

where --container kafka is to select the Kafka workload container of the unit. By default, the charm operator container is opened.

This file can be provided to the Kafka bin commands via the --command-config argument. Note that client.properties may also refer to other files ( e.g. truststore and keystore for TLS-enabled connections). Those files also need to be accessible and correctly specified.

Commands can be run within a Kafka broker, since both the authentication file (along with the truststore if needed) and the Charmed Kafka binaries are already present.

Listing topics example

For instance, to list the current topics on the Kafka cluster, you can run:

juju ssh --container kafka kafka-k8s/leader '/opt/kafka/bin/kafka-topics.sh --bootstrap-server $BOOTSTRAP_SERVERS --list --command-config /etc/kafka/client.properties'

As long as BOOTSTRAP_SERVERS variable contains the information we retrieved earlier in the Juju admins of the Kafka deployment section.

For example, a full command without the usage of the variable might look like the following:

juju ssh --container kafka kafka-k8s/leader '/opt/kafka/bin/kafka-topics.sh --bootstrap-server kafka-k8s-0.kafka-k8s-endpoints:9092,kafka-k8s-1.kafka-k8s-endpoints:9092,kafka-k8s-2.kafka-k8s-endpoints:9092,kafka-k8s-3.kafka-k8s-endpoints:9092 --list --command-config /etc/kafka/client.properties'

where kafka-k8s-0.kafka-k8s-endpoints:9092,kafka-k8s-1.kafka-k8s-endpoints:9092,kafka-k8s-2.kafka-k8s-endpoints:9092,kafka-k8s-3.kafka-k8s-endpoints:9092 - is the contents of the $BOOTSTRAP_SERVERS variable.

Juju external users

For external users managed by the Data Integrator Charm, the endpoints and credentials can be fetched using the dedicated action:

juju run data-integrator/leader get-credentials --format yaml

The client.properties file can be generated by substituting the relevant information in the file available on the brokers at /etc/kafka/client.properties.

To do so, fetch the information using juju commands:

BOOTSTRAP_SERVERS=$(juju run data-integrator/leader get-credentials --format yaml | yq .kafka.endpoints )
USERNAME=$(juju run data-integrator/leader get-credentials --format yaml | yq .kafka.username )
PASSWORD=$(juju run data-integrator/leader get-credentials --format yaml | yq .kafka.password )

Then copy the /etc/kafka/client.properties and substitute the following lines:

...
sasl.jaas.config=org.apache.kafka.common.security.scram.ScramLoginModule required username="<USERNAME>" password="<PASSWORD>";
...
bootstrap.servers=<BOOTSTRAP_SERVERS>