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:

[PARSER]
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.

Decoders

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.

Examples

escaped_utf8

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"}
{"log":"\u0009Done\n","stream":"stdout","time":"2018-02-19T23:25:29.1845622Z"}

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

[SERVICE]
Parsers_File fluent-bit-parsers.conf
[INPUT]
Name tail
Parser docker
Path /path/to/log.log
[OUTPUT]
Name stdout
Match *

The fluent-bit-parsers.conf file,

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