Parser Decoders

There are certain cases where the log messages being parsed contains encoded data, a typical use case can be found in containerized environments with Docker: application logs it data in JSON format but becomes an escaped string, Consider the following example

Original message generated by the application:

{"status": "up and running"}

Then the Docker log message become encapsulated as follows:

{"log":"{\"status\": \"up and running\"}\r\n","stream":"stdout","time":"2018-03-09T01:01:44.851160855Z"}

as you can see the original message is handled as an escaped string. Ideally in Fluent Bit we would like to keep having the original structured message and not a string.

Getting Started

Decoders are a built-in feature available through the Parsers file, each Parser definition can optionally set one or multiple decoders. There are two type of decoders type:

  • Decode_Field: if the content can be decoded in a structured message, append that structure message (keys and values) to the original log message.
  • Decode_Field_As: any content decoded (unstructured or structured) will be replaced in the same key/value, no extra keys are added.

Our pre-defined Docker Parser have the following definition:

    Name         docker
    Format       json
    Time_Key     time
    Time_Format  %Y-%m-%dT%H:%M:%S.%L
    Time_Keep    On
    # Command       |  Decoder  | Field | Optional Action   |
    # ==============|===========|=======|===================|
    Decode_Field_As    escaped     log

Each line in the parser with a key Decode_Field instruct the parser to apply a specific decoder on a given field, optionally it offer the option to take an extra action if the decoder cannot succeed.


Name Description
json handle the field content as a JSON map. If it find a JSON map it will replace the content with a structured map.
escaped decode an escaped string.
escaped_utf8 decode a UTF8 escaped string.

Optional Actions

By default if a decoder fails to decode the field or want to try a next decoder, is possible to define an optional action. Available actions are:

Name Description
try_next if the decoder failed, apply the next Decoder in the list for the same field.
do_next if the decoder succeeded or failed, apply the next Decoder in the list for the same field.

Note that actions are affected by some restrictions:

  • on Decode_Field_As, if succeeded, another decoder of the same type in the same field can be applied only if the data continue being a unstructed message (raw text).
  • on Decode_Field, if succeeded, can only be applied once for the same field. By nature Decode_Field aims to decode a structured message.



Example input (from /path/to/log.log in configuration below)

{"log":"\u0009Checking indexes...\n","stream":"stdout","time":"2018-02-19T23:25:29.1845444Z"}
{"log":"\u0009\u0009Validated: _audit _internal _introspection _telemetry _thefishbucket history main snmp_data summary\n","stream":"stdout","time":"2018-02-19T23:25:29.1845536Z"}

Example output

[24] tail.0: [1519082729.184544400, {"log"=>"   Checking indexes...                                                   
", "stream"=>"stdout", "time"=>"2018-02-19T23:25:29.1845444Z"}]
[25] tail.0: [1519082729.184553600, {"log"=>"           Validated: _audit _internal _introspection _telemetry _thefishbucket history main snmp_data summary
", "stream"=>"stdout", "time"=>"2018-02-19T23:25:29.1845536Z"}]
[26] tail.0: [1519082729.184562200, {"log"=>"   Done                  
", "stream"=>"stdout", "time"=>"2018-02-19T23:25:29.1845622Z"}]

Configuration file

    Parsers_File fluent-bit-parsers.conf

    Name        tail
    Parser      docker
    Path        /path/to/log.log

    Name   stdout
    Match  *

The fluent-bit-parsers.conf file,

    Name        docker
    Format      json
    Time_Key    time
    Time_Format %Y-%m-%dT%H:%M:%S %z
    Decode_Field_as escaped_utf8 log

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