[fluentd] filter/record에 예약어 존재

fluentd의 filter/record안에서는 예약어가 존재한다.

https://docs.fluentd.org/v0.12/articles/filter_record_transformer

<filter foo.bar>
  @type record_transformer
  <record>
    hostname "#{Socket.gethostname}"
    tag ${tag}
  </record>
</filter>

요청이 다음과 같이 들어오면.. 

{"message":"hello world!"}

hostname과 tag가 추가된다.

{"message":"hello world!", "hostname":"db001.internal.example.com", "tag":"foo.bar"}

중간에 Parameter 내용을 보면.. 

record 디렉티브 하위에 tag_xxx, tag, time, hostname을 사용할 수 있다고 한다.

예를 들어 time을 통해 발생 시간이 넘어온다.

Parameters

<record> directive

Parameters inside <record> directives are considered to be new key-value pairs:

<record>
  NEW_FIELD NEW_VALUE
</record>

For NEW_FIELD and NEW_VALUE, a special syntax ${} allows the user to generate a new field dynamically. Inside the curly braces, the following variables are available:

• The incoming event’s existing values can be referred by their field names. So, if the record is {"total":100, "count":10}, then record["total"]=100 and record["count"]=10.
• tag_parts[N] refers to the Nth part of the tag. It works like the usual zero-based array accessor.
• tag_prefix[N] refers to the first N parts of the tag. It works like the usual zero-based array accessor.
• tag_suffix[N] refers to the last N parts of the tag. It works like the usual zero-based array accessor.
• tag refers to the whole tag.
• time refers to stringanized event time.
• hostname refers to machine’s hostname. The actual value is result of Socket.gethostname.