exec_filter

The out_exec_filter Buffered Output plugin 1) executes an external program using an event as input; and, 2) reads a new event from the program output.

By default, it passes tab-separated values (TSV) to the standard input and reads TSV from the standard output.

It is included in Fluentd's core.

Example Configuration

<match pattern>
  @type exec_filter
  command cmd arg arg
  <format>
    @type tsv
    keys k1,k2,k3
  </format>
  <parse>
    @type tsv
    keys k1,k2,k3,k4
  </parse>
  <inject>
    tag_key k1
    time_key k2
    time_format %Y-%m-%d %H:%M:%S
  </inject>
</match>

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

When using the JSON format in <parse> section, this plugin uses the Yajl library to parse the program output. Yajl buffers data internally so the output is not always instantaneous.

If the buffering by Yajl parser is problematic for you even though you expect instantaneous response, you can tweak stream_buffer_size parameter in <parse> section.

Supported Modes

• Synchronous

• See also: Output Plugin Overview

Plugin Helpers

• compat_parameters

• inject

• formatter

• parser

• extract

• child_process

• event_emitter

Parameters

@type

The value must be exec_filter.

command

type	default	version
string	required parameter	0.14.0

The command (program) to execute. The out_exec_filter plugin passes the incoming event to the program input and receives the filtered event from the program output.

num_children

type	default	version
integer	1	0.14.0

The number of spawned processes for command.

If the number is larger than 2, fluentd uses spawned processes by round robin fashion.

child_respawn

type	default	version
string	nil	0.14.0

Respawn command when the command exits. By default, it is disabled.

If you specify a positive number, it tries to respawn until specified times. If you specify inf or -1, it tries to respawn forever.

tag

type	default	version
string	nil	0.14.0

The tag of the event.

read_block_size

type	default	version
size	10240	0.14.9

The default block size to read if parser requires partial read.

suppress_error_log_interval

type	default	version
time	0	0.14.0

Suppress error logs during this interval.

By default, all the logs are emitted.

in_format

This parameter is deprecated. Use <format> section.

The format used to map the incoming event to the program input.

out_format

This parameter is deprecated. Use <parse> section.

The format used to process the program output.

<format> Section

The format used to map the incoming events to the program input.

See Format Section Configurations for more details.

@type

type	default	version
string	tsv	0.14.9

Overwrites the default value in this plugin.

<parse> Section

The format used to process the program output.

See Parse Section Configurations for more details.

@type

type	default	version
string	tsv	0.14.9

Overwrites the default value in this plugin.

time_key

type	default	version
string	nil	0.14.9

Overwrites the default value in this plugin.

time_format

type	default	version
string	nil	0.14.9

Overwrites the default value in this plugin.

localtime

type	default	version
bool	true	0.14.9

Overwrites the default value in this plugin.

<inject> Section

See Inject Section Configurations for more details.

time_type

type	default	version
enum	float	0.14.9

Overwrites the default value in this plugin.

<extract> Section

See Extract Section Configurations for more details.

time_type

type	default	version
enum	float	0.14.9

Overwrite default value in this plugin.

<buffer> Section

See Buffer Section Configurations for more details.

flush_mode

type	default	version
enum	interval	0.14.9

Overwrites the default value in this plugin.

flush_interval

type	default	version
integer	1	0.14.9

Overwrites the default value in this plugin.

Script Example

Here is an example written in Ruby:

require 'json'
require 'msgpack'

begin
  while line = STDIN.gets # continue to read a event from stdin
    line.chomp!

    # Input format depends on exec_filter's in_format setting
    json = JSON.parse(line)

    # main processing. You can do anything, mutate record, access to database and etc.
    json['new_field'] = "Hey from exec_filter script!"

    # Write data to stdout. Output format depends on exec_filter's out_format setting
    STDOUT.print MessagePack.pack(json)

    # Call flush to avoid buffering events
    STDOUT.flush
  end
rescue Interrupt # Ignore Interrupt exception because it happens during exec_filter shutdown
end

Corresponding configuration:

<match test.**>
  @type exec_filter
  command ruby /path/to/ruby_script.rb
  tag filtered.exec
  <format>
    @type json
  </format>
  <parse>
    @type msgpack
  </parse>
  <buffer>
    flush_interval 10s
  </buffer>
</match>

You may convert this script into your preferred language accordingly.

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