Configuration File

This page describes the yaml configuration file used by Fluent Bit

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

YAML configuration is used in the smoke tests for containers, so an always-correct up-to-date example is here: https://github.com/fluent/fluent-bit/blob/master/packaging/testing/smoke/container/fluent-bit.yaml.

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:

Key	Description	Default Value
flush	Set the flush time in seconds.nanoseconds. The engine loop uses a Flush timeout to define when is required to flush the records ingested by input plugins through the defined output plugins.	5
grace	Set the grace time in seconds as an Integer value. The engine loop uses a Grace timeout to define the wait time on exit	5
daemon	Boolean value to set if Fluent Bit should run as a Daemon (background) or not. Allowed values are: yes, no, on, and off. note: If you are using a Systemd based unit like the one we provide in our packages, do not turn on this option.	Off
dns.mode	Sets the primary transport layer protocol used by the asynchronous DNS resolver, which can be overridden on a per plugin basis	UDP
log_file	Absolute path for an optional log file. By default, all logs are redirected to the standard error interface (stderr).
log_level	Set the logging verbosity level. Allowed values are: off, error, warn, info, debug and trace. Values are accumulative, e.g., if 'debug' is set, it will include error, warning, info, and debug. Note that trace mode is only available if Fluent Bit was built with the WITH_TRACE option enabled.	info
parsers_file	Path for a parsers configuration file. Multiple Parsers_File entries can be defined within the section.
plugins_file	Path for a plugins configuration file. A plugins configuration file allows the definition of paths for external plugins; for an example, see here.
streams_file	Path for the Stream Processor configuration file. To learn more about Stream Processing configuration go here.
http_server	Enable built-in HTTP Server	Off
http_listen	Set listening interface for HTTP Server when it's enabled	0.0.0.0
http_port	Set TCP Port for the HTTP Server	2020
coro_stack_size	Set the coroutines stack size in bytes. The value must be greater than the page size of the running system. Don't set too small a value (say 4096), or coroutine threads can overrun the stack buffer. Do not change the default value of this parameter unless you know what you are doing.	24576
scheduler.cap	Set a maximum retry time in seconds. The property is supported from v1.8.7.	2000
scheduler.base	Sets the base of exponential backoff. The property is supported from v1.8.7.	5
json.convert_nan_to_null	If enabled, NaN is converted to null when fluent-bit converts msgpack to json.	false
sp.convert_from_str_to_num	If enabled, Stream processor converts from number string to number type.	true

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 pipelinme 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:

Key	Description
Name	Name of the input plugin. Defined as subsection of the inputs section.
Tag	Tag name associated to all records coming from this plugin.
Log_Level	Set the plugin's logging verbosity level. Allowed values are: off, error, warn, info, debug and trace. Defaults to the SERVICE section's Log_Level.

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:

Key	Description
Name	Name of the filter plugin. Defined as a subsection of the filters section.
Match	A pattern to match against the tags of incoming records. It's case-sensitive and supports the star (*) character as a wildcard.
Match_Regex	A regular expression to match against the tags of incoming records. Use this option if you want to use the full regex syntax.
Log_Level	Set the plugin's logging verbosity level. Allowed values are: off, error, warn, info, debug and trace. Defaults to the SERVICE section's Log_Level.

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:

Key	Description
Name	Name of the output plugin. Defined as a subsection of the outputs section.
Match	A pattern to match against the tags of incoming records. It's case-sensitive and supports the star (*) character as a wildcard.
Match_Regex	A regular expression to match against the tags of incoming records. Use this option if you want to use the full regex syntax.
Log_Level	Set the plugin's logging verbosity level. Allowed values are: off, error, warn, info, debug and trace. The output log level defaults to the SERVICE section's Log_Level.

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