# kafka
The `out_kafka` Output plugin writes records into [Apache Kafka](https://kafka.apache.org/). This document doesn't describe all parameters. If you want to know full features, check the Further Reading section.
## Installation
`out_kafka` is included in td-agent2 after v2.3.3. Fluentd gem users will need to install the fluent-plugin-kafka gem using the following command.
```
$ fluent-gem install fluent-plugin-kafka
```
## Example Configuration
```
@type kafka_buffered
# list of seed brokers
brokers :,:
# buffer settings
buffer_type file
buffer_path /var/log/td-agent/buffer/td
flush_interval 3s
# topic settings
default_topic messages
# data type settings
output_data_type json
compression_codec gzip
# producer settings
max_send_retries 1
required_acks -1
```
Please see the [Config File](https://docs.fluentd.org/0.12/configuration/config-file) article for the basic structure and syntax of the configuration file.
Please make sure that you have **enough space in the buffer\_path directory**. Running out of disk space is a problem frequently reported by users.
## Parameters
### type (required)
The value must be `kafka_buffered`.
### brokers (required/optional)
The list of all seed brokers, with their host and port information.
### default\_topic
The name of default topic (default: nil).
### default\_partition\_key
The name of default partition key (default: nil).
### default\_message\_key
The name of default message key (default: nil).
### output\_data\_type
The format of each message. The available options are `json`, `ltsv`, `msgpack`, `attr:`, ``. `msgpack` is recommended since it's more compact and faster.
### max\_send\_retries
The number of times to retry sending of messages to a leader (default: 1).
### required\_acks
The number of acks required per request (default: -1).
### ack\_timeout
How long the producer waits for acks. The unit is seconds (default: nil => Use default of ruby-kafka library)
### compression\_codec
The codec the producer uses to compress messages (default: nil). The available options are `gzip` and `snappy`. When you use `snappy`, you need to install `snappy` gem by `td-agent-gem` command.
## Buffered Output Parameters
For advanced usage, you can tune Fluentd's internal buffering mechanism with these parameters.
### buffer\_type
The buffer type is `memory` by default ([buf\_memory](https://docs.fluentd.org/0.12/buffer/memory)) for the ease of testing, however `file` ([buf\_file](https://docs.fluentd.org/0.12/buffer/file)) buffer type is always recommended for the production deployments. If you use `file` buffer type, `buffer_path` parameter is required.
### buffer\_queue\_limit, buffer\_chunk\_limit
The length of the chunk queue and the size of each chunk, respectively. Please see the [Buffer Plugin Overview](https://docs.fluentd.org/0.12/buffer) article for the basic buffer structure. The default values are 64 and 8m, respectively. The suffixes "k" (KB), "m" (MB), and "g" (GB) can be used for buffer\_chunk\_limit.
### flush\_interval
The interval between data flushes. The default is 60s. The suffixes "s" (seconds), "m" (minutes), and "h" (hours) can be used.
### flush\_at\_shutdown
If set to true, Fluentd waits for the buffer to flush at shutdown. By default, it is set to true for Memory Buffer and false for File Buffer.
### retry\_wait, max\_retry\_wait
The initial and maximum intervals between write retries. The default values are 1.0 seconds and unset (no limit). The interval doubles (with +/-12.5% randomness) every retry until `max_retry_wait` is reached.
Since td-agent will retry 17 times before giving up by default (see the `retry_limit` parameter for details), the sleep interval can be up to approximately 131072 seconds (roughly 36 hours) in the default configurations.
### retry\_limit, disable\_retry\_limit
The limit on the number of retries before buffered data is discarded, and an option to disable that limit (if true, the value of `retry_limit` is ignored and there is no limit). The default values are 17 and false (not disabled). If the limit is reached, buffered data is discarded and the retry interval is reset to its initial value (`retry_wait`).
### num\_threads
The number of threads to flush the buffer. This option can be used to parallelize writes into the output(s) designated by the output plugin. Increasing the number of threads improves the flush throughput to hide write / network latency. The default is 1.
### slow\_flush\_log\_threshold
The threshold for checking chunk flush performance. The default value is `20.0` seconds. Note that parameter type is `float`, not `time`.
If chunk flush takes longer time than this threshold, fluentd logs warning message like below:
```
2016-12-19 12:00:00 +0000 [warn]: buffer flush took longer time than slow_flush_log_threshold: elapsed_time = 15.0031226690043695 slow_flush_log_threshold=10.0 plugin_id="foo"
```
#### log\_level option
The `log_level` option allows the user to set different levels of logging for each plugin. The supported log levels are: `fatal`, `error`, `warn`, `info`, `debug`, and `trace`.
Please see the [logging article](https://docs.fluentd.org/0.12/deployment/logging) for further details.
## Further Reading
This page doesn't describe all the possible configurations. If you want to know about other configurations, please check the link below.
* [fluent-plugin-kafka repository](https://github.com/fluent/fluent-plugin-kafka)
If this article is incorrect or outdated, or omits critical information, please [let us know](https://github.com/fluent/fluentd-docs-gitbook/issues?state=open). [Fluentd](http://www.fluentd.org/) is a open source project under [Cloud Native Computing Foundation (CNCF)](https://cncf.io/). All components are available under the Apache 2 License.