[[kafka-output]]
=== Configure the Kafka output

++++
<titleabbrev>Kafka</titleabbrev>
++++

The Kafka output sends the events to Apache Kafka.

Example configuration:

[source,yaml]
------------------------------------------------------------------------------
output.kafka:
  # initial brokers for reading cluster metadata
  hosts: ["kafka1:9092", "kafka2:9092", "kafka3:9092"]

  # message topic selection + partitioning
  topic: '%{[fields.log_topic]}'
  partition.round_robin:
    reachable_only: false

  required_acks: 1
  compression: gzip
  max_message_bytes: 1000000
------------------------------------------------------------------------------

NOTE: Events bigger than <<kafka-max_message_bytes,`max_message_bytes`>> will be dropped. To avoid this problem, make sure {beatname_uc} does not generate events bigger than <<kafka-max_message_bytes,`max_message_bytes`>>.

[[kafka-compatibility]]
==== Compatibility

This output works with all Kafka versions in between 0.11 and 2.2.2. Older versions
might work as well, but are not supported.

==== Configuration options

You can specify the following options in the `kafka` section of the +{beatname_lc}.yml+ config file:

===== `enabled`

The `enabled` config is a boolean setting to enable or disable the output. If set
to false, the output is disabled.

The default value is true.

===== `hosts`

The list of Kafka broker addresses from where to fetch the cluster metadata.
The cluster metadata contain the actual Kafka brokers events are published to.

===== `version`

Kafka version {beatname_lc} is assumed to run against. Defaults to 1.0.0.

Event timestamps will be added, if version 0.10.0.0+ is enabled.

Valid values are all kafka releases in between `0.8.2.0` and `2.0.0`.

See <<kafka-compatibility>> for information on supported versions.

===== `username`

The username for connecting to Kafka. If username is configured, the password
must be configured as well. Only SASL/PLAIN is supported.

===== `password`

The password for connecting to Kafka.

[[topic-option-kafka]]
===== `topic`

The Kafka topic used for produced events.

You can set the topic dynamically by using a format string to access any
event field. For example, this configuration uses a custom field,
`fields.log_topic`, to set the topic for each event:

[source,yaml]
-----
topic: '%{[fields.log_topic]}'
-----

TIP: To learn how to add custom fields to events, see the
<<libbeat-configuration-fields,`fields`>> option.

See the <<topics-option-kafka,`topics`>> setting for other ways to set the
topic dynamically.

[[topics-option-kafka]]
===== `topics`

An array of topic selector rules. Each rule specifies the `topic` to use for
events that match the rule. During publishing, {beatname_uc} sets the `topic`
for each event based on the first matching rule in the array. Rules
can contain conditionals, format string-based fields, and name mappings. If the
`topics` setting is missing or no rule matches, the
<<topic-option-kafka,`topic`>> field is used.

Rule settings:

*`topic`*:: The topic format string to use.  If this string contains field
references, such as `%{[fields.name]}`, the fields must exist, or the rule
fails.

*`mappings`*:: A dictionary that takes the value returned by `topic` and maps it
to a new name.

*`default`*:: The default string value to use if `mappings` does not find a
match.

*`when`*:: A condition that must succeed in order to execute the current rule.
ifndef::no-processors[]
All the <<conditions,conditions>> supported by processors are also supported
here.
endif::no-processors[]

The following example sets the topic based on whether the message field contains
the specified string:

["source","yaml",subs="attributes"]
------------------------------------------------------------------------------
output.kafka:
  hosts: ["localhost:9092"]
  topic: "logs-%{[agent.version]}"
  topics:
    - topic: "critical-%{[agent.version]}"
      when.contains:
        message: "CRITICAL"
    - topic: "error-%{[agent.version]}"
      when.contains:
        message: "ERR"
------------------------------------------------------------------------------


This configuration results in topics named +critical-{version}+,
+error-{version}+, and +logs-{version}+.

===== `key`

Optional formatted string specifying the Kafka event key. If configured, the
event key can be extracted from the event using a format string.

See the Kafka documentation for the implications of a particular choice of key;
by default, the key is chosen by the Kafka cluster.

===== `partition`

Kafka output broker event partitioning strategy. Must be one of `random`,
`round_robin`, or `hash`. By default the `hash` partitioner is used.

*`random.group_events`*: Sets the number of events to be published to the same
 partition, before the partitioner selects a new partition by random. The
 default value is 1 meaning after each event a new partition is picked randomly.

*`round_robin.group_events`*: Sets the number of events to be published to the
 same partition, before the partitioner selects the next partition. The default
 value is 1 meaning after each event the next partition will be selected.

*`hash.hash`*: List of fields used to compute the partitioning hash value from.
 If no field is configured, the events `key` value will be used.

*`hash.random`*: Randomly distribute events if no hash or key value can be computed.

All partitioners will try to publish events to all partitions by default. If a
partition's leader becomes unreachable for the beat, the output might block. All
partitioners support setting `reachable_only` to overwrite this
behavior. If `reachable_only` is set to `true`, events will be published to
available partitions only.

NOTE: Publishing to a subset of available partitions potentially increases resource usage because events may become unevenly distributed.

===== `client_id`

The configurable ClientID used for logging, debugging, and auditing purposes. The default is "beats".

===== `worker`

The number of concurrent load-balanced Kafka output workers.

===== `codec`

Output codec configuration. If the `codec` section is missing, events will be json encoded.

See <<configuration-output-codec>> for more information.

===== `metadata`

Kafka metadata update settings. The metadata do contain information about
brokers, topics, partition, and active leaders to use for publishing.

*`refresh_frequency`*:: Metadata refresh interval. Defaults to 10 minutes.

*`full`*:: Strategy to use when fetching metadata, when this option is `true`, the client will maintain
a full set of metadata for all the available topics, if the this option is set to `false` it will only refresh the
metadata for the configured topics. The default is false.

*`retry.max`*:: Total number of metadata update retries when cluster is in middle of leader election. The default is 3.

*`retry.backoff`*:: Waiting time between retries during leader elections. Default is 250ms.

===== `max_retries`

ifdef::ignores_max_retries[]
{beatname_uc} ignores the `max_retries` setting and retries indefinitely.
endif::[]

ifndef::ignores_max_retries[]
The number of times to retry publishing an event after a publishing failure.
After the specified number of retries, the events are typically dropped.

Set `max_retries` to a value less than 0 to retry until all events are published.

The default is 3.
endif::[]

===== `bulk_max_size`

The maximum number of events to bulk in a single Kafka request. The default is 2048.

===== `bulk_flush_frequency`

Duration to wait before sending bulk Kafka request. 0 is no delay. The default is 0.

===== `timeout`

The number of seconds to wait for responses from the Kafka brokers before timing
out. The default is 30 (seconds).

===== `broker_timeout`

The maximum duration a broker will wait for number of required ACKs. The default is 10s.

===== `channel_buffer_size`

Per Kafka broker number of messages buffered in output pipeline. The default is 256.

===== `keep_alive`

The keep-alive period for an active network connection. If 0s, keep-alives are disabled. The default is 0 seconds.

===== `compression`

Sets the output compression codec. Must be one of `none`, `snappy`, `lz4` and `gzip`. The default is `gzip`.

[IMPORTANT]
.Known issue with Azure Event Hub for Kafka
====
When targeting Azure Event Hub for Kafka, set `compression` to `none` as the provided codecs are not supported.
====

===== `compression_level`

Sets the compression level used by gzip. Setting this value to 0 disables compression.
The compression level must be in the range of 1 (best speed) to 9 (best compression).

Increasing the compression level will reduce the network usage but will increase the cpu usage.

The default value is 4.

[[kafka-max_message_bytes]]
===== `max_message_bytes`

The maximum permitted size of JSON-encoded messages. Bigger messages will be dropped. The default value is 1000000 (bytes). This value should be equal to or less than the broker's `message.max.bytes`.

===== `required_acks`

The ACK reliability level required from broker. 0=no response, 1=wait for local commit, -1=wait for all replicas to commit. The default is 1.

Note: If set to 0, no ACKs are returned by Kafka. Messages might be lost silently on error.

===== `ssl`

Configuration options for SSL parameters like the root CA for Kafka connections.
 The Kafka host keystore should be created with the
`-keyalg RSA` argument to ensure it uses a cipher supported by
https://github.com/Shopify/sarama/wiki/Frequently-Asked-Questions#why-cant-sarama-connect-to-my-kafka-cluster-using-ssl[Filebeat's Kafka library].
See <<configuration-ssl>> for more information.
