How to expand JSON in Fluentd?

Is there a way to filter out the nested JSON string out into separate fields in fluentd?

Current JSON:

 { 
   Value1: "something",
   Value2: "something",
   Message:{
             Value3: "Something",
             Value3: "Something"
          }
 }

What I want (or something similar):

 { 
   Value1: "something",
   Value2: "something",
   Message.Value3: "Something",
   Message.Value3: "Something"
          
 }

The JSON doesn't have to be flatten like in above example but I do want the values to be in their own separate fields(columns) when they reach elasticsearch. In other wards, I want to split the single long Message string into multiple fields contained within it.

Solution

Try this:

<source>
...
</source>

<filter myapp**>
  @type parser
  key_name Message

  format multi_format
  <pattern>
    format json # try parsing json in the first place
  </pattern>
  <pattern>
    format none # leave as is if this is not json (plaintext)
  </pattern>

  reserve_data true # keep the original Message field in case anything go wrong
</filter>

<match myapp**>
...
</match>

Multi-format parser: https://github.com/repeatedly/fluent-plugin-multi-format-parser