The in_forward Input plugin listens to a TCP socket to receive the event stream. It also listens to an UDP socket to receive heartbeat messages.

This plugin is mainly used to receive event logs from other Fluentd instances, the fluent-cat command, or client libraries. This is by far the most efficient way to retrieve the records. Do NOT use this plugin for inter-DC or public internet data transfer without secure connections. To provide the reliable / low-latency transfer, we assume this plugin is only used within private networks.

If you open up the port of this plugin to the internet, the attacker can easily crash Fluentd by using the specific packet. If you require a secure connection between nodes, please consider using in_secure_forward.

Example Configuration

in_forward is included in Fluentd's core. No additional installation process is required.

  @type forward
  port 24224

Please see the Config File article for the basic structure and syntax of the configuration file.


type (required)

The value must be forward.


The port to listen to. Default Value = 24224


The bind address to listen to. Default Value = (all addresses)


The timeout time used to set linger option. The default is 0


The size limit of the the received chunk. If the chunk size is larger than this value, then the received chunk is dropped. The default is nil (no limit).


The warning size limit of the received chunk. If the chunk size is larger than this value, a warning message will be sent. The default is nil (no warning).

skip_invalid_event (v0.12.20 or later)

Skip an event if incoming event is invalid. The default is false.

This option is useful at forwarder, not aggragator. v0.12.20 or later.

source_hostname_key (v0.12.28 or later)

The field name of the client's hostname. If set the value, the client's hostname will be set to its key. The default is nil (no adding hostname).

This iterates incoming events. So if you sends larger chunks to in_forward, it needs additional processing time.

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 for further details.


This plugin accepts both JSON or MessagePack messages and automatically detects which is used. Internally, Fluent uses MessagePack as it is more efficient than JSON.

The time value is a platform specific integer and is based on the output of Ruby's function. On Linux, BSD and MAC systems, this is the number of seconds since 1970.

Multiple messages may be sent in the same connection.


  [tag, time, record]
  [tag, [[time,record], [time,record], ...]]

  ["myapp.access", 1308466941, {"a":1}]["myapp.messages", 1308466942, {"b":2}]
  ["myapp.access", [[1308466941, {"a":1}], [1308466942, {"b":2}]]]

Communication with v1.0

v0.12 in_forward can't accept data from v1.0 out_forward because time format is different. If you want to forward data from v1.0 to v0.12, set time_as_integer in v1.0 out_forward.


Why in_forward doesn't have tag parameter?

in_forward uses tag of incoming events so no fixed tag parameter. See above "Protocol" section.

How to parse incoming events?

in_forward doesn't provide parsing mechanism unlike in_tail or in_tcp because in_forward is mainly for efficient log transfer. If you want to parse incoming event, use parser filter in your pipeline. See Docker logging driver usecase: Docker Logging

I got MessagePack::UnknownExtTypeError error. Why?

This error happens when forwarder's fluentd is v0.14/v1.0 and receiver's fluentd is 0.12. To avoid this problem, set time_as_integer to out_forward setting in v0.14/v1.0 fluentd. See "Communication with v1.0".

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.

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