Configures a Kafka Connect cluster.

The `config` properties are one part of the overall configuration for the resource.
Use the `config` properties to configure Kafka Connect options as keys.

.Example Kafka Connect configuration
[source,yaml,subs="attributes+"]
----
apiVersion: {KafkaConnectApiVersion}
kind: KafkaConnect
metadata:
  name: my-connect
spec:
  # ...
  config:
    group.id: my-connect-cluster
    offset.storage.topic: my-connect-cluster-offsets
    config.storage.topic: my-connect-cluster-configs
    status.storage.topic: my-connect-cluster-status
    key.converter: org.apache.kafka.connect.json.JsonConverter
    value.converter: org.apache.kafka.connect.json.JsonConverter
    key.converter.schemas.enable: true
    value.converter.schemas.enable: true
    config.storage.replication.factor: 3
    offset.storage.replication.factor: 3
    status.storage.replication.factor: 3
  # ...
----

The values can be one of the following JSON types:

* String
* Number
* Boolean

Certain options have default values:

* `group.id` with default value `connect-cluster`
* `offset.storage.topic` with default value `connect-cluster-offsets`
* `config.storage.topic` with default value `connect-cluster-configs`
* `status.storage.topic` with default value `connect-cluster-status`
* `key.converter` with default value `org.apache.kafka.connect.json.JsonConverter`
* `value.converter` with default value `org.apache.kafka.connect.json.JsonConverter`

These options are automatically configured in case they are not present in the `KafkaConnect.spec.config` properties.

*Exceptions*

You can specify and configure the options listed in the {ApacheKafkaConnectConfig}.

However, Strimzi takes care of configuring and managing options related to the following, which cannot be changed:

* Kafka cluster bootstrap address
* Security (encryption, authentication, and authorization)
* Listener and REST interface configuration
* Plugin path configuration

Properties with the following prefixes cannot be set:

* `bootstrap.servers`
* `consumer.interceptor.classes`
* `listeners.`
* `plugin.path`
* `producer.interceptor.classes`
* `rest.`
* `sasl.`
* `security.`
* `ssl.`

If the `config` property contains an option that cannot be changed, it is disregarded, and a warning message is logged to the Cluster Operator log file.
All other supported options are forwarded to Kafka Connect, including the following exceptions to the options configured by Strimzi:

* Any `ssl` configuration for xref:con-common-configuration-ssl-reference[supported TLS versions and cipher suites]

IMPORTANT: The Cluster Operator does not validate keys or values in the `config` object provided.
If an invalid configuration is provided, the Kafka Connect cluster might not start or might become unstable.
In this case, fix the configuration so that the Cluster Operator can roll out the new configuration to all Kafka Connect nodes.

[id='property-kafka-connect-logging-{context}']
= Logging
Kafka Connect has its own configurable loggers:

* `connect.root.logger.level`
* `log4j.logger.org.reflections`

Further loggers are added depending on the Kafka Connect plugins running.

Use a curl request to get a complete list of Kafka Connect loggers running from any Kafka broker pod:

[source,curl,subs=attributes+]
----
curl -s http://<connect-cluster-name>-connect-api:8083/admin/loggers/
----

Kafka Connect uses the Apache `log4j` logger implementation.

Use the `logging` property to configure loggers and logger levels.

You can set the log levels by specifying the logger and level directly (inline) or use a custom (external) ConfigMap.
If a ConfigMap is used, you set `logging.valueFrom.configMapKeyRef.name` property to the name of the ConfigMap containing the external logging configuration. Inside the ConfigMap, the logging configuration is described using `log4j.properties`. Both `logging.valueFrom.configMapKeyRef.name` and `logging.valueFrom.configMapKeyRef.key` properties are mandatory. A ConfigMap using the exact logging configuration specified is created with the custom resource when the Cluster Operator is running, then recreated after each reconciliation. If you do not specify a custom ConfigMap, default logging settings are used. If a specific logger value is not set, upper-level logger settings are inherited for that logger.
For more information about log levels, see {ApacheLoggers}.

Here we see examples of `inline` and `external` logging.
The `inline` logging specifies the root logger level.
You can also set log levels for specific classes or loggers by adding them to the loggers property.

.Inline logging
[source,yaml,subs="+quotes,attributes"]
----
apiVersion: {KafkaConnectApiVersion}
kind: KafkaConnect
spec:
  # ...
  logging:
    type: inline
    loggers:
      connect.root.logger.level: INFO
      log4j.logger.org.apache.kafka.connect.runtime.WorkerSourceTask: TRACE
      log4j.logger.org.apache.kafka.connect.runtime.WorkerSinkTask: DEBUG
  # ...
----

NOTE: Setting a log level to `DEBUG` may result in a large amount of log output and may have performance implications.

.External logging
[source,yaml,subs="+quotes,attributes"]
----
apiVersion: {KafkaConnectApiVersion}
kind: KafkaConnect
spec:
  # ...
  logging:
    type: external
    valueFrom:
      configMapKeyRef:
        name: customConfigMap
        key: connect-logging.log4j
  # ...
----

Any available loggers that are not configured have their level set to `OFF`.

If Kafka Connect was deployed using the Cluster Operator,
changes to Kafka Connect logging levels are applied dynamically.

If you use external logging, a rolling update is triggered when logging appenders are changed.

.Garbage collector (GC)

Garbage collector logging can also be enabled (or disabled) using the xref:con-common-configuration-garbage-collection-reference[`jvmOptions` property].
