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configuration-file.md

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This page describes the main configuration file used by Fluent Bit.

Configuration file

One of the ways to configure Fluent Bit is using a main configuration file. Fluent Bit allows the use one configuration file that works at a global scope and uses the defined Format and Schema.

The main configuration file supports four sections:

  • Service
  • Input
  • Filter
  • Output

It's also possible to split the main configuration file into multiple files using the Include File feature to include external files.

Service

The Service section defines global properties of the service. The following keys are:

Key Description Default Value
flush Set the flush time in seconds.nanoseconds. The engine loop uses a Flush timeout to define when it's required to flush the records ingested by input plugins through the defined output plugins. 1
grace Set the grace time in seconds as an integer value. The engine loop uses a grace timeout to define wait time on exit. 5
daemon Boolean. Determines whether Fluent Bit should run as a Daemon (background). Allowed values are: yes, no, on, and off. Don't enable when using a Systemd based unit, such as the one provided in Fluent Bit packages.   Off
dns.mode Set the primary transport layer protocol used by the asynchronous DNS resolver. 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). none
log_level Set the logging verbosity level. Allowed values are: off, error, warn, info, debug, and trace. Values are cumulative. If debug is set, it will include error, warning, info, and debug. 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. none
plugins_file Path for a plugins configuration file. A plugins configuration file defines paths for external plugins. See an example. none
streams_file Path for the Stream Processor configuration file. Learn more about Stream Processing configuration. none
http_server Enable the 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. Setting the value too small (4096) can cause coroutine threads to overrun the stack buffer. The default value of this parameter shouldn't be changed. 24576
scheduler.cap Set a maximum retry time in seconds. Supported in v1.8.7 and greater. 2000
scheduler.base Set a base of exponential backoff. Supported in v1.8.7 and greater. 5
json.convert_nan_to_null If enabled, NaN converts 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, see scheduling and retries.

Config input

The INPUT section defines a source (related to an input plugin). Each input plugin can add its own configuration keys:

Key Description
Name Name of the input plugin.
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.

Name is mandatory and tells Fluent Bit which input plugin to load. Tag is mandatory for all plugins except for the input forward plugin, which provides dynamic tags.

Example

The following is an example of an INPUT section:

[INPUT]
    Name cpu
    Tag  my_cpu

Config filter

The FILTER section defines a filter (related to an filter plugin). Each filter plugin can add it own configuration keys. The base configuration for each FILTER section contains:

Key Description
Name Name of the filter plugin.
Match A pattern to match against the tags of incoming records. Case sensitive, supports asterisk (*) 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 regular expression 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.

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

Filter example

The following is an example of a FILTER section:

[FILTER]
    Name  grep
    Match *
    Regex log aa

Config output

The OUTPUT section specifies a destination that certain records should go to after a Tag match. Fluent Bit can route up to 256 OUTPUT plugins. The configuration supports the following keys:

Key Description
Name Name of the output plugin.
Match A pattern to match against the tags of incoming records. Case sensitive and supports the asterisk (*) 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 regular expression 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.

Output example

The following is an example of an OUTPUT section:

[OUTPUT]
    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

[INPUT]
    Name  cpu
    Tag   my_cpu

[OUTPUT]
    Name  stdout
    Match my*cpu

Config Include File

To avoid complicated long configuration files is better to split specific parts in different files and call them (include) from one main file. The @INCLUDE can be used in the following way:

@INCLUDE somefile.conf

The configuration reader will try to open the path somefile.conf. If not found, the reader assumes the file is on a relative path based on the path of the base configuration file:

  • Main configuration path: /tmp/main.conf
  • Included file: somefile.conf
  • Fluent Bit will try to open somefile.conf, if it fails it will try /tmp/somefile.conf.

The @INCLUDE command only works at top-left level of the configuration line, and can't be used inside sections.

Wildcard character (*) supports including multiple files. For example:

@INCLUDE input_*.conf

Files matching the wildcard character are included unsorted. If plugin ordering between files needs to be preserved, the files should be included explicitly.