How to manage related applications

Relations to new applications are supported via the “kafka_client” interface.

Within Juju via kafka_client interface

If the charm supports the kafka_client interface, just create a relation between the two charms:

juju relate kafka application

To remove a relation:

juju remove-relation kafka application

Outside Juju or for charms not implementing kafka_client

The kafka_client interface is used with the data-integrator charm. This charm automatically creates and manages product credentials needed to authenticate with different kinds of data platform charmed products:

Deploy the Data Integrator charm with the desired topic-name and user roles:

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

Relate the two applications with:

juju relate data-integrator kafka

To retrieve information, enter:

juju run data-integrator/leader get-credentials

This should output something like:

kafka:
  consumer-group-prefix: relation-27-
  endpoints: 10.123.8.133:19092
  password: ejMp4SblzxkMCF0yUXjaspneflXqcyXK
  tls: disabled
  username: relation-27
  zookeeper-uris: 10.123.8.154:2181,10.123.8.181:2181,10.123.8.61:2181/kafka
ok: "True"

Password rotation

Password rotation can be performed in multiple ways, depending on the requirements.

External clients

There are two ways to rotate credentials of an external client. One is simply to delete and re-create the relation, the other one can be performed without any downtime.

With client application downtime

The easiest way to rotate user credentials of client applications is by removing and then re-relating the application (either a charm supporting the kafka-client interface or a data-integrator) with the kafka charm:

juju remove-relation kafka <charm-or-data-integrator>
# wait for the relation to be torn down 
juju relate kafka <charm-or-data-integrator>

The successful credential rotation can be confirmed by retrieving the new password with the action get-credentials.

Without client application downtime

In some use-cases credentials should be rotated with no or limited application downtime. If credentials should be rotated with no or limited downtime, you can deploy a new charm with the same permissions and resource definition, for example:

juju deploy data-integrator rotated-user --channel stable \
  --config topic-name=test-topic --config extra-user-roles=admin

The data-integrator charm can then be related to the kafka charm to create a new user:

juju relate kafka rotated-user

At this point, we effectively have two overlapping users, so that applications can swap the password from one to another. If the applications consist of fleets of independent producers and consumers, user credentials can be rotated progressively across fleets, such that no effective downtime is achieved.

Once all applications have rotated their credentials, it is then safe to remove data first data-integrator charm

juju remove-application data-integrator

Internal password rotation

The operator user is used internally by the Charmed Kafka Operator, the set-password action can be used to rotate its password.

# to set a specific password for the operator user
juju run kafka/leader set-password password=<password>

# to randomly generate a password for the operator user
juju run kafka/leader set-password