Configuration File

There are some cases where using the command line to start Fluent Bit is not ideal. When running Fluent Bit as a service, a configuration file is preferred.

Fluent Bit allows to use one configuration file which works at a global scope and uses the schema defined previously.

The configuration file supports four types of sections:

In addition there is an additional feature to include external files:

Service

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

Key Description Default Value
Flush Set the flush time in seconds. Everytime it timeouts, the engine will flush the records to the output plugin. 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. Off
Log_File Absolute path for an optional log file.
Log_Level Set the logging verbosity level. Allowed values are: error, warning, 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 used.
Plugins_File Path for a plugins configuration file. A plugins configuration file allows to define paths for external plugins, for an example see here.
Streams_File Path for the Stream Processor configuration file. For details about the format of SP configuration file see 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 value (say 4096), or coroutine threads can overrun the stack buffer. 24576

Example

The following is an example of a SERVICE section:

  1. [SERVICE]
  2.     Flush           5
  3.     Daemon          off
  4.     Log_Level       debug

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.
Tag Tag name associated to all records comming from this plugin.

The Name is mandatory and it let 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

The following is an example of an INPUT section:

  1. [INPUT]
  2.     Name cpu
  3.     Tag  my_cpu

Filter

A FILTER section defines a filter (related to an filter plugin), here we will describe the base configuration for each FILTER section. Note that each filter plugin may add it own configuration keys:

Key Description
Name Name of the filter plugin.
Match A pattern to match against the tags of incoming records. It’s case sensitive and support 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.

The Name is mandatory and it let 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

The following is an example of an FILTER section:

  1. [FILTER]
  2.     Name  stdout
  3.     Match *

Output

The OUTPUT section specify a destination that certain records should follow after a Tag match. The configuration support the following keys:

Key Description
Name Name of the output plugin.
Match A pattern to match against the tags of incoming records. It’s case sensitive and support 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.

Example

The following is an example of an OUTPUT section:

  1. [OUTPUT]
  2.     Name  stdout
  3.     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:

  1. [SERVICE]
  2.     Flush     5
  3.     Daemon    off
  4.     Log_Level debug
  6. [INPUT]
  7.     Name  cpu
  8.     Tag   my_cpu
  10. [OUTPUT]
  11.     Name  stdout
  12.     Match my*cpu

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.

Starting from Fluent Bit 0.12 the new configuration command @INCLUDE has been added and can be used in the following way:

  1. @INCLUDE somefile.conf

The configuration reader will try to open the path somefile.conf, if not found, it will assume it’s a relative path based on the path of the base configuration file, e.g:

  • Main configuration file 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, it cannot be used inside sections.

Wildcard character (*) is supported to include multiple files, e.g:

  1. @INCLUDE input_*.conf