Charmed Kafka Documentation - Tutorial Relate Kafka

This is part of the Charmed Kafka Tutorial. Please refer to this page for more information and the overview of the content.

Integrate with client applications

As mentioned in the previous section of the Tutorial, the recommended way to create and manage users is by means of another charm: the Data Integrator Charm. This will allow us to encode users directly in the Juju model, and - as shown in the following - to rotate user credentials rotations with and without application downtime using Relations.

Relations, or what Juju documentation describes also as Integration, allow two charms to exchange information and interact with one another. Creating a relation between Kafka and the Data Integrator will allow us to automatically create a username, password, and topic for the desired user/application, and this is indeed the easiest way to create and manage users for Kafka in Charmed Kafka.

Data Integrator Charm

The Data Integrator Charm is a bare-bones charm that allows for central management of database users, providing support for different kinds of data platforms (e.g. MongoDB, MySQL, PostgreSQL, Kafka, OpenSearch, etc) with a consistent, opinionated and robust user experience. In order to deploy the Data Integrator Charm we can use the command juju deploy we have learned above:

juju deploy data-integrator --channel stable --config topic-name=test-topic --config extra-user-roles=producer,consumer

The expected output:

Located charm "data-integrator" in charm-hub, revision 11
Deploying "data-integrator" from charm-hub charm "data-integrator", revision 11 in channel stable on jammy

Relate to Kafka

Now that the Database Integrator Charm has been set up, we can relate it to Kafka. This will automatically create a username, password, and database for the Database Integrator Charm. Relate the two applications with:

juju relate data-integrator kafka

Wait for juju status --watch 1s to show:

Model     Controller  Cloud/Region         Version  SLA          Timestamp
tutorial  overlord    localhost/localhost  3.1.6    unsupported  10:04:50Z

App              Version  Status  Scale  Charm            Channel      Rev  Exposed  Message
data-integrator           active      1  data-integrator  stable        11  no       
kafka                     active      3  kafka            3/stable     147  no       
zookeeper                 active      5  zookeeper        3/stable     114  no       

Unit                Workload  Agent  Machine  Public address  Ports  Message
data-integrator/0*  active    idle   8            
kafka/0             active    idle   5           machine system settings are not optimal - see logs for info
kafka/1*            active    idle   6            machine system settings are not optimal - see logs for info
kafka/2             active    idle   7           machine system settings are not optimal - see logs for info
zookeeper/0         active    idle   0          
zookeeper/1         active    idle   1          
zookeeper/2         active    idle   2          
zookeeper/3*        active    idle   3           
zookeeper/4         active    idle   4          

Machine  State    Address        Inst id        Series  AZ  Message
0        started  juju-f1a2cd-0  jammy       Running
1        started  juju-f1a2cd-1  jammy       Running
2        started  juju-f1a2cd-2  jammy       Running
3        started   juju-f1a2cd-3  jammy       Running
4        started  juju-f1a2cd-4  jammy       Running
5        started   juju-f1a2cd-5  jammy       Running
6        started    juju-f1a2cd-6  jammy       Running
7        started   juju-f1a2cd-7  jammy       Running
8        started    juju-f1a2cd-8  jammy       Running

To retrieve information such as the username, password, and topic. Enter:

juju run data-integrator/leader get-credentials

This should output something like:

  consumer-group-prefix: relation-6-
  password: ILg8C5msYRvqOnGATeFPyw2DKHncritf
  tls: disabled
  topic: test-topic
  username: relation-6
ok: "True"

Save the value listed under bootstrap-server, username and password. (Note: your hostnames, usernames, and passwords will likely be different.)

Produce/Consume messages

We will now use the username and password to produce some messages to Kafka. To do so, we will first deploy the Kafka Test App (available here): a test charm that also bundles some python scripts to push data to Kafka, e.g.

juju deploy kafka-test-app -n1 --channel edge

Once the charm is up and running, you can log into the container

juju ssh kafka-test-app/0 /bin/bash

and make sure that the Python virtual environment libraries are visible:

export PYTHONPATH="/var/lib/juju/agents/unit-kafka-test-app-0/charm/venv:/var/lib/juju/agents/unit-kafka-test-app-0/charm/lib"

Once this is setup, you should be able to use the script that exposes some functionality to produce and consume messages. You can explore the usage of the script

python3 -m charms.kafka.v0.client --help

                 [--producer] [--consumer] [--cafile-path CAFILE_PATH] [--certfile-path CERTFILE_PATH] [--keyfile-path KEYFILE_PATH] [--mongo-uri MONGO_URI] [--origin ORIGIN]

Handler for running a Kafka client

  -h, --help            show this help message and exit
  -t TOPIC, --topic TOPIC
                        Kafka topic provided by Kafka Charm
  -u USERNAME, --username USERNAME
                        Kafka username provided by Kafka Charm
  -p PASSWORD, --password PASSWORD
                        Kafka password provided by Kafka Charm
                        Kafka consumer-group-prefix provided by Kafka Charm
  -s SERVERS, --servers SERVERS
                        comma delimited list of Kafka bootstrap-server strings
                        security protocol used for authentication
  -n NUM_MESSAGES, --num-messages NUM_MESSAGES
                        number of messages to send from a producer
                        replcation.factor for created topics
  --num-partitions NUM_PARTITIONS
                        partitions for created topics
  --cafile-path CAFILE_PATH
  --certfile-path CERTFILE_PATH
  --keyfile-path KEYFILE_PATH
  --mongo-uri MONGO_URI
  --origin ORIGIN

Using this script, you can therefore start producing messages (change the values of username, password and servers)

python3 -m charms.kafka.v0.client \
  -u relation-6 -p S4IeRaYaiiq0tsM7m2UZuP2mSI573IGV \
  -t test-topic \
  -s ",," \
  -n 10 --producer \
  -r 3 --num-partitions 1

and consume them

python3 -m charms.kafka.v0.client \
  -u relation-6 -p S4IeRaYaiiq0tsM7m2UZuP2mSI573IGV \
  -t test-topic \
  -s ",," \
  --consumer \
  -c "cg"

Charm Client Applications

Actually, the Data Integrator is only a very special client charm, that implements the kafka_client relation for exchanging data with the Kafka charm and allowing user management via relations.

For example, the steps above for producing and consuming messages to Kafka have also been implemented in the kafka-test-app charm (that also implement the kafka_client relation) providing a fully integrated charmed user-experience, where producing/consuming messages can simply be achieved using relations.

Producing messages

To produce messages to Kafka, we need to configure the kafka-test-app to act as producer, publishing messages to a specific topic

juju config kafka-test-app topic_name=test_kafka_app_topic role=producer num_messages=20

To start producing messages to Kafka, we JUST simply relate the Kafka Test App with Kafka

juju relate kafka-test-app kafka

Note This will both take care of creating a dedicated user (as much as done for the data-integrator) as well as start a producer process publishing messages to the test_kafka_app_topic topic, basically automating what was done before by hands.

After some time, the juju status output should show

Model     Controller  Cloud/Region         Version  SLA          Timestamp
tutorial  overlord    localhost/localhost  3.1.6    unsupported  18:58:47+02:00

App              Version  Status  Scale  Charm            Channel  Rev  Address         Exposed  Message
kafka-test-app            active      1  kafka-test-app   edge       8   no       Topic test_kafka_app_topic enabled with process producer

Unit                Workload  Agent  Address     Ports  Message
kafka-test-app/0*   active    idle         Topic test_kafka_app_topic enabled with process producer

indicating that the process has started. To make sure that this is indeed the case, you can check the logs of the process:

juju exec --application kafka-test-app "tail /tmp/*.log"

To stop the process (although it is very likely that the process has already stopped given the low number of messages that were provided) and remove the user, you can just remove the relation

juju remove-relation kafka-test-app kafka

Consuming messages

Note that the kafka-test-app charm can also similarly be used to consume messages by changing its configuration to

juju config kafka-test-app topic_name=test_kafka_app_topic role=consumer consumer_group_prefix=cg

After configuring the Kafka Test App, just relate it again with the Kafka charm. This will again create a new user and start the consumer process.

What’s next?

In the next section, we will learn how to rotate and manage the passwords for the Kafka users, both the admin one and the ones managed by the data-integrator.