Adjusting librdkafka settings

To set rdkafka options - add to <kafka> section in config.xml or preferably use a separate file in config.d/:
- https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md

Some random example:

<yandex>
    <kafka>
        <max_poll_interval_ms>60000</max_poll_interval_ms>
        <session_timeout_ms>60000</session_timeout_ms>
        <heartbeat_interval_ms>10000</heartbeat_interval_ms>
        <reconnect_backoff_ms>5000</reconnect_backoff_ms>
        <reconnect_backoff_max_ms>60000</reconnect_backoff_max_ms>
        <request_timeout_ms>20000</request_timeout_ms>
        <retry_backoff_ms>500</retry_backoff_ms>
        <message_max_bytes>20971520</message_max_bytes>
        <debug>all</debug><!-- only to get the errors -->
        <security_protocol>SSL</security_protocol>
        <ssl_ca_location>/etc/clickhouse-server/ssl/kafka-ca-qa.crt</ssl_ca_location>
        <ssl_certificate_location>/etc/clickhouse-server/ssl/client_clickhouse_client.pem</ssl_certificate_location>
        <ssl_key_location>/etc/clickhouse-server/ssl/client_clickhouse_client.key</ssl_key_location>
        <ssl_key_password>pass</ssl_key_password>
    </kafka>
</yandex>

Authentication / connectivity

Amazon MSK

<yandex>
  <kafka>
    <security_protocol>sasl_ssl</security_protocol>
    <sasl_username>root</sasl_username>
    <sasl_password>toor</sasl_password>
  </kafka>
</yandex>

SASL/SCRAM

<yandex>
  <kafka>
    <security_protocol>sasl_ssl</security_protocol>
    <sasl_mechanism>SCRAM-SHA-512</sasl_mechanism>
    <sasl_username>root</sasl_username>
    <sasl_password>toor</sasl_password>
  </kafka>
</yandex>

https://leftjoin.ru/all/clickhouse-as-a-consumer-to-amazon-msk/

Inline Kafka certs

To connect to some Kafka cloud services you may need to use certificates.

If needed they can be converted to pem format and inlined into ClickHouse config.xml Example:

<kafka>
<ssl_key_pem><![CDATA[
  RSA Private-Key: (3072 bit, 2 primes)
    ....
-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----
]]></ssl_key_pem>
<ssl_certificate_pem><![CDATA[
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
]]></ssl_certificate_pem>
</kafka>

See xml

https://help.aiven.io/en/articles/489572-getting-started-with-aiven-kafka

https://stackoverflow.com/questions/991758/how-to-get-pem-file-from-key-and-crt-files

Azure Event Hub

See https://github.com/ClickHouse/ClickHouse/issues/12609

Kerberos

  <!-- Kerberos-aware Kafka -->
  <kafka>
    <security_protocol>SASL_PLAINTEXT</security_protocol>
    <sasl_kerberos_keytab>/home/kafkauser/kafkauser.keytab</sasl_kerberos_keytab>
    <sasl_kerberos_principal>kafkauser/kafkahost@EXAMPLE.COM</sasl_kerberos_principal>
  </kafka>

confluent cloud

<yandex>
  <kafka>
    <auto_offset_reset>smallest</auto_offset_reset>
    <security_protocol>SASL_SSL</security_protocol>
    <ssl_endpoint_identification_algorithm>https</ssl_endpoint_identification_algorithm>
    <sasl_mechanism>PLAIN</sasl_mechanism>
    <sasl_username>username</sasl_username>
    <sasl_password>password</sasl_password>
    <ssl_ca_location>probe</ssl_ca_location>
    <!--
    <ssl_ca_location>/path/to/cert.pem</ssl_ca_location>      
    -->
  </kafka>
</yandex>

https://docs.confluent.io/cloud/current/client-apps/config-client.html

How to test connection settings

Use kafkacat utility - it internally uses same library to access Kafla as clickhouse itself and allows easily to test different settings.

kafkacat -b my_broker:9092 -C -o -10 -t my_topic \
   -X security.protocol=SASL_SSL  \
   -X sasl.mechanisms=PLAIN \
   -X sasl.username=uerName \
   -X sasl.password=Password

Different configurations for different tables?

Is there some more documentation how to use this multiconfiguration for Kafka ?

The whole logic is here: https://github.com/ClickHouse/ClickHouse/blob/da4856a2be035260708fe2ba3ffb9e437d9b7fef/src/Storages/Kafka/StorageKafka.cpp#L466-L475

So it load the main config first, after that it load (with overwrites) the configs for all topics, listed in kafka_topic_list of the table.

Also since v21.12 it’s possible to use more straght-forward way using named_collections: https://github.com/ClickHouse/ClickHouse/pull/31691

So you can say something like

CREATE TABLE test.kafka (key UInt64, value UInt64) ENGINE = Kafka(kafka1, kafka_format='CSV');

And after that in configuration:

<clickhouse>
 <named_collections>
  <kafka1>
   <kafka_broker_list>kafka1:19092</kafka_broker_list>
   <kafka_topic_list>conf</kafka_topic_list>
   <kafka_group_name>conf</kafka_group_name>
  </kafka1>
 </named_collections>
</clickhouse>


<yandex>
    <named_collections>
        <kafka_preset1>
            <kafka_broker_list>...</kafka_broker_list>
            <kafka_topic_list>foo.bar</kafka_topic_list>
            <kafka_group_name>foo.bar.group</kafka_group_name>
            <kafka>
                <security_protocol>...</security_protocol>
                <sasl_mechanism>...</sasl_mechanism>
                <sasl_username>...</sasl_username>
                <sasl_password>...</sasl_password>
                <auto_offset_reset>smallest</auto_offset_reset>
                <ssl_endpoint_identification_algorithm>https</ssl_endpoint_identification_algorithm>
                <ssl_ca_location>probe</ssl_ca_location>
            </kafka>
        </kafka_preset1>
    </named_collections>
</yandex>

The same fragment of code in newer versions: https://github.com/ClickHouse/ClickHouse/blob/d19e24f530c30f002488bc136da78f5fb55aedab/src/Storages/Kafka/StorageKafka.cpp#L474-L496

Last modified 2023.02.02: fix idents (82bbca4)