The child_process helper manages child processes' lifecycle.

Here is an example:

require 'fluent/plugin/output'
​
module Fluent::Plugin
  class ExampleOutput < Output
    Fluent::Plugin.register_output('example', self)
​
    # 1. Load child_process helper
    helpers :child_process
​
    # Omit configure, shutdown and other plugin API
​
    def start
      super
      # 2. Execute child process with unique name
      child_process_execute(:exec_external_command, 'external_command', immediate: true, mode: [:read]) do
        # ...
      end
    end
  end
end

The launched child process is managed by the plugin helper which automatically shutdowns it.

Methods

child_process_execute(title, sub_process_name, arguments: nil, subprocess_name: nil, interval: nil, immediate: false, parallel: false, mode: [:read, :write], stderr: :discard, env: {}, unsetenv: false, chdir: nil, internal_encoding: 'utf-8', external_encoding: 'ascii-8bit', scrub: true, replace_string: nil, wait_timeout: nil, on_exit_callback: nil, &block)

This method executes child_process with given parameters and routine.

• title: unique symbol value

• sub_process_name: sub process name value

• interval: Second unit integer/float value.

• immediate: true/false. Default is false.

• parallel: true/false. Default is false.

• mode: [:read, :write]. Default is [:read, :write].

• stderr: Connect stderr or not. Default is :discard.

• env: Environment valuables. Default is {}.

• unsetenv: true/false. Default is false

• chdir: Working directory. Default is nil.

• internal_encoding: Internal character encoding. Default is

  utf-8.

• external_encoding: External character encoding. Default is

  ascii-8bit'

• scrub: true/false. Default is true.

• replace_string: Replace invalid code point with specified

  character. Default is nil.

• wait_timeout: Set timeout seconds. Default is nil.

• on_exit_callback: Set callback function. Default is nil

Code examples:

# Pass block directly. block is executed with 10 second interval.
child_process_execute(:exec_awesome_command, @command, interval: 10, mode: [:read]) do |io|
  # ...
end
​
# Pass block with existing method. block is executed once.
child_process_execute(:exec_awesome_command, @command, immediate: true, mode: [:read], &method(:run))
​
def run(io)
  # ...
end

Plugins using child_process

• ​in_exec​

• ​out_exec​

• ​out_exec_filter​

If this article is incorrect or outdated, or omits critical information, please let us know.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.