---
title: Configure the Kafka output
description: The Kafka output sends events to Apache Kafka. To use this output, edit the APM Server configuration file to disable the Elasticsearch output by commenting...
url: https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5399/solutions/observability/apm/apm-server/configure-kafka-output
products:
  - APM
  - Elastic Observability
applies_to:
  - Elastic Stack: Generally available
---

# Configure the Kafka output
<note>
  ![supported deployment methods](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5399/solutions/images/observability-binary-yes-fm-no.svg)The Kafka output is not yet supported by Fleet-managed APM Server.
</note>

The Kafka output sends events to Apache Kafka.
To use this output, edit the APM Server configuration file to disable the Elasticsearch output by commenting it out, and enable the Kafka output by uncommenting the Kafka section.
Example configuration:
```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 [`max_message_bytes`](#apm-kafka-max_message_bytes) will be dropped. To avoid this problem, make sure APM Server does not generate events bigger than [`max_message_bytes`](#apm-kafka-max_message_bytes).
</note>


## 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 `apm-server.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 `false`.

### `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 apm-server 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 [Compatibility](#apm-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.

### `password`

The password for connecting to Kafka.

### `sasl.mechanism`

<warning>
  This functionality is in beta and is subject to change. The design and code is less mature than official GA features and is being provided as-is with no warranties. Beta features are not subject to the support SLA of official GA features.
</warning>

The SASL mechanism to use when connecting to Kafka. It can be one of:
- `PLAIN` for SASL/PLAIN.
- `SCRAM-SHA-256` for SCRAM-SHA-256.
- `SCRAM-SHA-512` for SCRAM-SHA-512.

If `sasl.mechanism` is not set, `PLAIN` is used if `username` and `password` are provided. Otherwise, SASL authentication is disabled.

### `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:
```yaml
topic: '%{[fields.log_topic]}'
```

See the [`topics`](#apm-topics-option-kafka) setting for other ways to set the topic dynamically.

### `topics`

An array of topic selector rules. Each rule specifies the `topic` to use for events that match the rule. During publishing, APM Server 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`](#apm-topic-option-kafka) field is used.
Rule settings:
<definitions>
  <definition term="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.
  </definition>
  <definition term="mappings">
    A dictionary that takes the value returned by `topic` and maps it to a new name.
  </definition>
  <definition term="default">
    The default string value to use if `mappings` does not find a match.
  </definition>
  <definition term="when">
    A condition that must succeed in order to execute the current rule.
  </definition>
</definitions>

The following example sets the topic based on whether the message field contains the specified string:
```yaml
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-9.3.1_, _error-9.3.1_, and _logs-9.3.1_.

### `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.
</note>


### `client_id`

The configurable client ID 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 [Change the output codec](/elastic/docs-content/pull/5399/solutions/observability/apm/apm-server/configure-console-output#apm-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.
<definitions>
  <definition term="refresh_frequency">
    Metadata refresh interval. Defaults to 10 minutes.
  </definition>
  <definition term="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.
  </definition>
  <definition term="retry.max">
    Total number of metadata update retries when cluster is in middle of leader election. The default is 3.
  </definition>
  <definition term="retry.backoff">
    Waiting time between retries during leader elections. Default is `250ms`.
  </definition>
</definitions>


### `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.

### `backoff.init`

The number of seconds to wait before trying to republish to Kafka after a network error. After waiting `backoff.init` seconds, APM Server tries to republish. If the attempt fails, the backoff timer is increased exponentially up to `backoff.max`. After a successful publish, the backoff timer is reset. The default is `1s`.

### `backoff.max`

The maximum number of seconds to wait before attempting to republish to Kafka after a network error. The default is `60s`.

### `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 `0s`.

### `compression`

Sets the output compression codec. Must be one of `none`, `snappy`, `lz4` and `gzip`. The default is `gzip`.
<admonition title="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.
</admonition>


### `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.

### `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.

### `enable_krb5_fast`

<warning>
  This functionality is in beta and is subject to change. The design and code is less mature than official GA features and is being provided as-is with no warranties. Beta features are not subject to the support SLA of official GA features.
</warning>

Enable Kerberos FAST authentication. This may conflict with some Active Directory installations. It is separate from the standard Kerberos settings because this flag only applies to the Kafka output. The default is `false`.

### `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 [Filebeat's Kafka library](https://github.com/Shopify/sarama/wiki/Frequently-Asked-Questions#why-cant-sarama-connect-to-my-kafka-cluster-using-ssl). See [SSL/TLS output settings](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5399/solutions/observability/apm/apm-server/ssl-tls-output-settings) for more information.