Kafka output plugin allows to ingest your records into an Apache Kafka service. This plugin use the official librdkafka C library (built-in dependency)

Configuration Parameters



Specify data format, options available: json, msgpack, raw.



Optional key to store the message


If set, the value of Message_Key_Field in the record will indicate the message key. If not set nor found in the record, Message_Key will be used (if set).


Set the key to store the record timestamp



Specify timestamp format, should be 'double', 'iso8601' (seconds precision) or 'iso8601_ns' (fractional seconds precision)



Single or multiple list of Kafka Brokers, e.g:,


Single entry or list of topics separated by comma (,) that Fluent Bit will use to send messages to Kafka. If only one topic is set, that one will be used for all records. Instead if multiple topics exists, the one set in the record by Topic_Key will be used.



If multiple Topics exists, the value of Topic_Key in the record will indicate the topic to use. E.g: if Topic_Key is router and the record is {"key1": 123, "router": "route_2"}, Fluent Bit will use topic route_2. Note that if the value of Topic_Key is not present in Topics, then by default the first topic in the Topics list will indicate the topic to be used.


adds unknown topics (found in Topic_Key) to Topics. So in Topics only a default topic needs to be configured



Fluent Bit queues data into rdkafka library, if for some reason the underlying library cannot flush the records the queue might fills up blocking new addition of records. The queue_full_retries option set the number of local retries to enqueue the data. The default value is 10 times, the interval between each retry is 1 second. Setting the queue_full_retries value to 0 set's an unlimited number of retries.



{property} can be any librdkafka properties


When using the raw format and set, the value of raw_log_key in the record will be send to kafka as the payload.


This setting improves the throughput and performance of data forwarding by enabling concurrent data processing and transmission to the kafka output broker destination.


Setting rdkafka.log.connection.close to false and rdkafka.request.required.acks to 1 are examples of recommended settings of librdfkafka properties.

Getting Started

In order to insert records into Apache Kafka, you can run the plugin from the command line or through the configuration file:

Command Line

The kafka plugin can read parameters through the -p argument (property), e.g:

$ fluent-bit -i cpu -o kafka -p brokers= -p topics=test

Configuration File

In your main configuration file append the following Input & Output sections:

    Name  cpu

    Name        kafka
    Match       *
    Topics      test

Avro Support

Fluent-bit comes with support for avro encoding for the out_kafka plugin. Avro support is optional and must be activated at build-time by using a build def with cmake: -DFLB_AVRO_ENCODER=On such as in the following example which activates:

  • out_kafka with avro encoding

  • fluent-bit's prometheus

  • metrics via an embedded http endpoint

  • debugging support

  • builds the test suites


Kafka Configuration File with Avro Encoding

This is example fluent-bit config tails kubernetes logs, decorates the log lines with kubernetes metadata via the kubernetes filter, and then sends the fully decorated log lines to a kafka broker encoded with a specific avro schema.

    Name              tail
    Tag               kube.*
    Alias             some-alias
    Path              /logdir/*.log
    DB                /dbdir/some.db
    Skip_Long_Lines   On
    Refresh_Interval  10
    Parser some-parser

    Name                kubernetes
    Match               kube.*
    Kube_URL            https://some_kube_api:443
    Kube_CA_File        /certs/ca.crt
    Kube_Token_File     /tokens/token
    Kube_Tag_Prefix     kube.var.log.containers.
    Merge_Log           On
    Merge_Log_Key       log_processed

    Name        kafka
    Match       *
    Topics      test
    Schema_str  {"name":"avro_logging","type":"record","fields":[{"name":"timestamp","type":"string"},{"name":"stream","type":"string"},{"name":"log","type":"string"},{"name":"kubernetes","type":{"name":"krec","type":"record","fields":[{"name":"pod_name","type":"string"},{"name":"namespace_name","type":"string"},{"name":"pod_id","type":"string"},{"name":"labels","type":{"type":"map","values":"string"}},{"name":"annotations","type":{"type":"map","values":"string"}},{"name":"host","type":"string"},{"name":"container_name","type":"string"},{"name":"docker_id","type":"string"},{"name":"container_hash","type":"string"},{"name":"container_image","type":"string"}]}},{"name":"cluster_name","type":"string"},{"name":"fabric","type":"string"}]}
    Schema_id some_schema_id
    rdkafka.client.id some_client_id
    rdkafka.debug All
    rdkafka.enable.ssl.certificate.verification true

    rdkafka.ssl.certificate.location /certs/some.cert
    rdkafka.ssl.key.location /certs/some.key
    rdkafka.ssl.ca.location /certs/some-bundle.crt
    rdkafka.security.protocol ssl
    rdkafka.request.required.acks 1
    rdkafka.log.connection.close false

    Format avro
    rdkafka.log_level 7

Kafka Configuration File with Raw format

This example Fluent Bit configuration file creates example records with the payloadkey and msgkey keys. The msgkey value is used as the Kafka message key, and the payloadkey value as the payload.

    Name example
    Tag  example.data
    Dummy {"payloadkey":"Data to send to kafka", "msgkey": "Key to use in the message"}

    Name        kafka
    Match       *
    Topics      test
    Format      raw

    Raw_Log_Key       payloadkey
    Message_Key_Field msgkey

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