Filter plugin to modify event record for Fluentd

Adding arbitary field to event record without customizing existence plugin.

For example, generated event from in_tail doesn't contain "hostname" of running machine.
In this case, you can use record_modifier to add "hostname" field to event record.

Requirements

Installation

Use RubyGems:

fluent-gem install fluent-plugin-record-modifier --no-document

Configuration

Use record_modifier filter.

<filter pattern>
  @type record_modifier

  <record>
    gen_host "#{Socket.gethostname}"
    foo bar
  </record>
</filter>

If following record is passed:

{"message":"hello world!"}

then you got new record like below:

{"message":"hello world!", "gen_host":"oreore-mac.local", "foo":"bar"}

You can also use record_transformer like ${xxx} placeholders and access tag, time, record and tag_parts values by Ruby code.

<filter pattern>
  @type record_modifier

  <record>
    tag ${tag}
    tag_extract ${tag_parts[0]}-${tag_parts[1]}-foo
    formatted_time ${Time.at(time).to_s}
    new_field foo:${record['key1'] + record['dict']['key']} 
  </record>
</filter>

record_modifier is faster than record_transformer. See this comment.
But unlike record_transformer, record_modifier doesn't support following features for now.

• tag_suffix and tag_prefix
• dynamic key placeholder

prepare_value

Prepare values for filtering. This ruby code is evaluated in configure phase and prepared values can be used in <record>. Here is an example:

<filter pattern>
  @type record_modifier
  prepare_value require 'foo'; @foo = Foo.new
  <record>
    key ${@foo.method1}
  </record>
</filter>

This feature is useful for using external library.

char_encoding

Fluentd including some plugins treats logs as a BINARY by default to forward.
But a user sometimes wants to process logs depends on their requirements, e.g. handling char encoding correctly.

char_encoding parameter is useful for this case.

<filter pattern>
  @type record_modifier

  # set UTF-8 encoding information to string.
  char_encoding utf-8

  # change char encoding from 'UTF-8' to 'EUC-JP'
  char_encoding utf-8:euc-jp
</filter>

In char_encoding from:to case, it replaces invalid character with safe character.

remove_keys

The logs include needless record keys in some cases.
You can remove it by using remove_keys parameter.

<filter pattern>
  @type record_modifier

  # remove key1 and key2 keys from record
  remove_keys key1,key2
</filter>

If following record is passed:

{"key1":"hoge", "key2":"foo", "key3":"bar"}

then you got new record like below:

{"key3":"bar"}

Since v2.2.0, remove_keys supports nested key delete via record_accessor syntax.

whitelist_keys

If you want to handle the set of explicitly specified keys, you can use whitelist_keys of this plugin. It's exclusive with remove_keys.

<filter pattern>
  @type record_modifier

  # remove all keys except for key1 and key2
  whitelist_keys key1,key2
</filter>

If following record is passed:

{"key1":"hoge", "key2":"foo", "key3":"bar"}

then you got new record like below:

{"key1":"hoge", "key2":"foo"}

replace_keys_value

If you want to replace specific value for keys you can use replace section.

<filter pattern>
  @type record_modifier

  # replace key key1
  <replace>
    # your key name
    key key1
    # your regexp
    expression /^(?<start>.+).{2}(?<end>.+)$/
    # replace string
    replace \k<start>ors\k<end>
  </replace>
  # replace key key2
  <replace>
    # your key name
    key key2
    # your regexp
    expression /^(.{1}).{2}(.{1})$/
    # replace string
    replace \1ors\2
  </replace>
</filter>

If following record is passed:

{"key1":"hoge", "key2":"hoge", "key3":"bar"}

then you got new record like below:

{"key1":"horse", "key2":"horse", "key3":"bar"}

Ruby code trick for complex logic

If you need own complex logic in filter, writing filter plugin is better. But if you don't want to write new plugin, you can use temporal key trick like below:

<filter reform.**>
  @type record_modifier
  remove_keys _dummy_
  <record>
    _dummy_ ${if record.has_key?('foo'); record['bar'] = 'Hi!'; end; nil}
  </record>
</filter>

record_modifier output

Output plugin version of record_modifier filter. If you want to process events and change tag at the same time, this plugin is useful.

<match pattern>
  @type record_modifier
  tag foo.${record["field1"]}

  <record>
    gen_host "#{Socket.gethostname}"
    foo bar
  </record>
</match>

Copyright