One of the ways to configure Fluent Bit is using a YAML configuration file that works at a global scope.

The YAML configuration file supports the following sections:

• Env

• Includes

• Service

• Pipeline

  • Inputs

  • Filters

  • Outputs

The YAML configuration file does not support the following sections yet:

• Parsers

Env

The env section allows the definition of configuration variables that will be used later in the configuration file.

Example:

# setting up a local environment variable
env:
    flush_interval: 1

# service configuration
service:
    flush:       ${flush_interval}
    log_level:   info
    http_server: on

Includes

The includes section allows the files to be merged into the YAML configuration to be identified as a list of filenames. If no path is provided, then the file is assumed to be in a folder relative to the file referencing it.

Example:

# defining file(s) to include into the current configuration. This includes illustrating using a relative path reference
includes:
    - inclusion-1.yaml
    - subdir/inclusion-2.yaml

Service

The service section defines the global properties of the service. The Service keys available as of this version are described in the following table:

The following is an example of a service section:

service:
    flush: 5
    daemon: off
    log_level: debug

For scheduler and retry details, please check there: scheduling and retries

Pipeline

A pipeline section will define a complete pipeline configuration, including inputs, filters and outputs subsections.

pipeline:
    inputs:
        ...
    filters:
        ...
    outputs:
        ...

Each of the subsections for inputs, filters and outputs constitutes an array of maps that has the parameters for each. Most properties are either simple strings or numbers so can be define directly, ie:

pipeline:
    inputs:
        - name: tail
          tag: syslog
          path: /var/log/syslog
        - name: http
          tag: http_server
          port: 8080

This pipeline consists of two inputs; a tail plugin and an http server plugin. Each plugin has its own map in the array of inputs consisting of simple properties. To use more advanced properties that consist of multiple values the property itself can be defined using an array, ie: the record and allowlist_key properties for the record_modifier filter:

pipeline:
    inputs:
        - name: tail
          tag: syslog
          path: /var/log/syslog
    filters:
        - name: record_modifier
          match: syslog
          record:
              - powered_by calyptia
        - name: record_modifier
          match: syslog
          allowlist_key:
              - powered_by
              - message

In the cases where each value in a list requires two values they must be separated by a space, such as in the record property for the record_modifier filter.

Input

An input section defines a source (related to an input plugin). Here we will describe the base configuration for each input section. Note that each input plugin may add it own configuration keys:

The Name is mandatory and it lets Fluent Bit know which input plugin should be loaded. The Tag is mandatory for all plugins except for the input forward plugin (as it provides dynamic tags).

Example input

The following is an example of an input section for the cpu plugin.

pipeline:
    inputs:
        - name: cpu
          tag: my_cpu

Filter

A filter section defines a filter (related to a filter plugin). Here we will describe the base configuration for each filter section. Note that each filter plugin may add its own configuration keys:

The Name is mandatory and it lets Fluent Bit know which filter plugin should be loaded. The Match or Match_Regex is mandatory for all plugins. If both are specified, Match_Regex takes precedence.

Example filter

The following is an example of a filter section for the grep plugin:

pipeline:
    filters:
        - name: grep
          match: '*'
          regex: log aa

Output

The outputs section specify a destination that certain records should follow after a Tag match. Currently, Fluent Bit can route up to 256 OUTPUT plugins. The configuration supports the following keys:

Example output

The following is an example of an output section:

pipeline:
    outputs:
        - name: stdout
          match: 'my*cpu'

Example: collecting CPU metrics

The following configuration file example demonstrates how to collect CPU metrics and flush the results every five seconds to the standard output:

service:
    flush: 5
    daemon: off
    log_level: debug

pipeline:
    inputs:
        - name: cpu
          tag: my_cpu
    outputs:
        - name: stdout
          match: 'my*cpu'

Processors

In recent versions of Fluent-Bit, the input and output plugins can run in separate threads. In Fluent-Bit 2.1.2, we have implemented a new interface called "processor" to extend the processing capabilities in input and output plugins directly without routing the data. This interface allows users to apply data transformations and filtering to incoming data records before they are processed further in the pipeline.

This functionality is only exposed in YAML configuration and not in classic configuration mode due to the restriction of nested levels of configuration.

Processor example

Example: Using processors.

The following configuration file example demonstrates the use of processors to change the log record in the input plugin section by adding a new key "hostname" with the value "monox", and we use lua to append the tag to the log record. Also in the ouput plugin section we added a new key named "output" with the value "new data". All these without the need of routing the logs further in the pipeline.

  service:
    log_level: info
    http_server: on
    http_listen: 0.0.0.0
    http_port: 2021
  pipeline:
    inputs:
      - name: random
        tag: test-tag
        interval_sec: 1
        processors:
          logs:
            - name: modify
              add: hostname monox
            - name: lua
              call: append_tag
              code: |
                  function append_tag(tag, timestamp, record)
                     new_record = record
                     new_record["tag"] = tag
                     return 1, timestamp, new_record
                  end
    outputs:
      - name: stdout
        match: '*'
        processors:
          logs:
            - name: lua
              call: add_field
              code: |
                  function add_field(tag, timestamp, record)
                     new_record = record
                     new_record["output"] = "new data"
                     return 1, timestamp, new_record
                  end

YAML configuration feature was introduced since FLuent Bit version 1.9 as experimental, and it is production ready since Fluent Bit 2.0.