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This page describes the main configuration file used by Fluent Bit
One of the ways to configure Fluent Bit is using a main configuration file. Fluent Bit allows to use one configuration file which works at a global scope and uses the Format and Schema defined previously.
The main configuration file supports four types of sections:
Service
Input
Filter
Output
In addition, it's also possible to split the main configuration file in multiple files using the feature to include external files:
Include File
The Service section defines global properties of the service, the keys available as of this version are described in the following table:
The following is an example of a SERVICE section:
For scheduler and retry details, please check there: scheduling and retries
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 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).
The following is an example of an INPUT section:
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:
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.
The following is an example of an FILTER section:
The OUTPUT 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 support the following keys:
The following is an example of an OUTPUT section:
The following configuration file example demonstrates how to collect CPU metrics and flush the results every five seconds to the standard output:
You can also visualize Fluent Bit INPUT, FILTER, and OUTPUT configuration via Calyptia
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:
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:
Note files matching the wildcard character are included unsorted. If plugins ordering between files need to be preserved, the files should be included explicitly.
Fluent Bit might optionally use a configuration file to define how the service will behave.
Before proceeding we need to understand how the configuration schema works.
The schema is defined by three concepts:
Sections
Entries: Key/Value
Indented Configuration Mode
A simple example of a configuration file is as follows:
A section is defined by a name or title inside brackets. Looking at the example above, a Service section has been set using [SERVICE] definition. Section rules:
All section content must be indented (4 spaces ideally).
Multiple sections can exist on the same file.
A section is expected to have comments and entries, it cannot be empty.
Any commented line under a section, must be indented too.
End-of-line comments are not supported, only full-line comments.
A section may contain Entries, an entry is defined by a line of text that contains a Key and a Value, using the above example, the [SERVICE]
section contains two entries, one is the key Daemon with value off and the other is the key Log_Level with the value debug. Entries rules:
An entry is defined by a key and a value.
A key must be indented.
A key must contain a value which ends in the breakline.
Multiple keys with the same name can exist.
Also commented lines are set prefixing the # character, those lines are not processed but they must be indented too.
Fluent Bit configuration files are based in a strict Indented Mode, that means that each configuration file must follow the same pattern of alignment from left to right when writing text. By default an indentation level of four spaces from left to right is suggested. Example:
As you can see there are two sections with multiple entries and comments, note also that empty lines are allowed and they do not need to be indented.
Key | Description | Default Value |
---|---|---|
Key | Description |
---|---|
Key | Description |
---|---|
Key | Description |
---|---|
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.
1
grace
Set the grace time in seconds
as Integer value. The engine loop uses a Grace timeout to define 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 as the one we provide in our packages, do not turn on this option.
Off
dns.mode
Set 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 to define 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 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 second. The property is supported from v1.8.7.
2000
scheduler.base
Set a 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
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
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.
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
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.
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.
Configuration files must be flexible enough for any deployment need, but they must keep a clean and readable format.
Fluent Bit Commands extends a configuration file with specific built-in features. The list of commands available as of Fluent Bit 0.12 series are:
Configuring a logging pipeline might lead to an extensive configuration file. In order to maintain a human-readable configuration, it's suggested to split the configuration in multiple files.
The @INCLUDE command allows the configuration reader to include an external configuration file, e.g:
The above example defines the main service configuration file and also include two files to continue the configuration:
Note that despites the order of inclusion, Fluent Bit will ALWAYS respect the following order:
Service
Inputs
Filters
Outputs
Fluent Bit supports configuration variables, one way to expose this variables to Fluent Bit is through setting a Shell environment variable, the other is through the @SET command.
The @SET command can only be used at root level of each line, meaning it cannot be used inside a section, e.g:
Fluent Bit supports the usage of environment variables in any value associated to a key when using a configuration file.
The variables are case sensitive and can be used in the following format:
When Fluent Bit starts, the configuration reader will detect any request for ${MY_VARIABLE}
and will try to resolve its value.
When Fluent Bit is running under systemd (using the official packages), environment variables can be set in the following files:
/etc/default/fluent-bit
(Debian based system)
/etc/sysconfig/fluent-bit
(Others)
These files are ignored if they do not exist.
Create the following configuration file (fluent-bit.conf
):
Open a terminal and set the environment variable:
The above command set the 'stdout' value to the variable
MY_OUTPUT
.
Run Fluent Bit with the recently created configuration file:
As you can see the service worked properly as the configuration was valid.
A full feature set to access content of your records
Fluent Bit works internally with structured records and it can be composed of an unlimited number of keys and values. Values can be anything like a number, string, array, or a map.
Having a way to select a specific part of the record is critical for certain core functionalities or plugins, this feature is called Record Accessor.
consider Record Accessor a simple grammar to specify record content and other miscellaneous values.
A record accessor rule starts with the character $
. Using the structured content above as an example the following table describes how to access a record:
The following table describe some accessing rules and the expected returned value:
If the accessor key does not exist in the record like the last example $labels['undefined']
, the operation is simply omitted, no exception will occur.
The file content to process in test.log
is the following:
Running Fluent Bit with the configuration above the output will be:
The Fluent Bit record_accessor library has a limitation in the characters that can separate template variables- only dots and commas (.
and ,
) can come after a template variable. This is because the templating library must parse the template and determine the end of a variable.
The following would be invalid templates because the two template variables are not separated by commas or dots:
$TaskID-$ECSContainerName
$TaskID/$ECSContainerName
$TaskID_$ECSContainerName
$TaskIDfooo$ECSContainerName
However, the following are valid:
$TaskID.$ECSContainerName
$TaskID.ecs_resource.$ECSContainerName
$TaskID.fooo.$ECSContainerName
And the following are valid since they only contain one template variable with nothing after it:
fooo$TaskID
fooo____$TaskID
fooo/bar$TaskID
An Upstream defines a set of nodes that will be targeted by an output plugin, by the nature of the implementation an output plugin must support the Upstream feature. The following plugin(s) have Upstream support:
The current balancing mode implemented is round-robin.
To define an Upstream it's required to create an specific configuration file that contains an UPSTREAM and one or multiple NODE sections. The following table describe the properties associated to each section. Note that all of them are mandatory:
A Node might contain additional configuration keys required by the plugin, on that way we provide enough flexibility for the output plugin, a common use case is Forward output where if TLS is enabled, it requires a shared key (more details in the example below).
In addition to the properties defined in the table above, the network operations against a defined node can optionally be done through the use of TLS for further encryption and certificates use.
The following example defines an Upstream called forward-balancing which aims to be used by Forward output plugin, it register three Nodes:
node-1: connects to 127.0.0.1:43000
node-2: connects to 127.0.0.1:44000
node-3: connects to 127.0.0.1:45000 using TLS without verification. It also defines a specific configuration option required by Forward output called shared_key.
Note that every Upstream definition must exists on it own configuration file in the file system. Adding multiple Upstreams in the same file or different files is not allowed.
Command | Prototype | Description |
---|---|---|
Format | Accessed Value |
---|
The feature is enabled on a per plugin basis, not all plugins enable this feature. As an example consider a configuration that aims to filter records using that only matches where labels have a color blue:
It's common that Fluent Bit aims to connect to external services to deliver the logs over the network, this is the case of , and within others. Being able to connect to one node (host) is normal and enough for more of the use cases, but there are other scenarios where balancing across different nodes is required. The Upstream feature provides such capability.
Section | Key | Description |
---|
The TLS options available are described in the section and can be added to the any Node section.
@INCLUDE FILE
Include a configuration file
@SET KEY=VAL
Set a configuration variable
$log | "some message" |
$labels['color'] | "blue" |
$labels['project']['env'] | "production" |
$labels['unset'] | null |
$labels['undefined'] |
UPSTREAM | name | Defines a name for the Upstream in question. |
NODE | name | Defines a name for the Node in question. |
host | IP address or hostname of the target host. |
port | TCP port of the target service. |