​Fluent Bit is an open source and multi-platform log processor tool which aims to be a generic Swiss knife for logs processing and distribution.

Nowadays the number of sources of information in our environments is ever increasing. Handling data collection at scale is complex, and collecting and aggregating diverse data requires a specialized tool that can deal with:

• Different sources of information

• Different data formats

• Data Reliability

• Security

• Flexible Routing

• Multiple destinations

Fluent Bit has been designed with performance and low resources consumption in mind.

Logging and data processing in general can be complex, and substantially more so at scale. That's why Fluentd was born. Now, Fluentd is more than a simple tool. It's a full ecosystem that contains SDKs for different languages and sub projects like Fluent Bit.

On this page, we will describe the relationship between the Fluentd and Fluent Bit open source projects. As a summary, we can say both are:

• Licensed under the terms of Apache License v2.0

• Hosted projects by the Cloud Native Computing Foundation (CNCF)

• Production Grade solutions: deployed thousands of times every single day, millions per month.

• Community driven projects

• Widely Adopted by the Industry: trusted by all major companies like AWS, Microsoft, Google Cloud and hundred of others.

• Originally created by Treasure Data.

Both projects have a lot of similarities. Fluent Bit is fully designed and built on top of the best ideas of the Fluentd architecture and general design. Choosing which one to use depends on the end-user needs.

The following table describes a comparison in different areas of the projects:

Both Fluentd and Fluent Bit can work as Aggregators or Forwarders. They can both complement each other or be used as standalone solutions.

Before diving into it’s good to get acquainted with some of the key concepts of the service. This document provides a gentle introduction to those concepts and common terminology. We’ve provided a list below of all the terms we’ll cover, but we recommend reading this document from start to finish to gain a more general understanding of our log and stream processor.

• Event or Record

• Filtering

• Tag

• Timestamp

• Match

• Structured Message

Event or Record

Every incoming piece of data that belongs to a log or a metric that is retrieved by Fluent Bit is considered an Event or a Record.

As an example consider the following content of a Syslog file:

It contains four lines and each of them represents an independent Event, for a total of four Events.

Internally, an Event always has two components (in an array form):

Filtering

Some cases require modifications on the Events content. Modifying events by altering, enriching or dropping Events is called Filtering.

There are many use cases when Filtering is required like:

• Append specific information to the Event like an IP address or metadata.

• Select a specific piece of the Event content.

• Drop Events that matches certain pattern.

Tag

Every Event that gets into Fluent Bit gets assigned a Tag. This tag is an internal string that is used in a later stage by the Router to decide which Filter or Output phase it must go through.

Most of the tags are assigned manually in the configuration. If a tag is not specified, Fluent Bit will assign the name of the Input plugin instance from where that Event was generated from.

Timestamp

The Timestamp represents the time when an Event was created. Every Event contains a Timestamp associated. The Timestamp is a numeric fractional integer in the format:

Seconds

It is the number of seconds that have elapsed since the Unix epoch.

Nanoseconds

Fractional second or one thousand-millionth of a second.

Match

Fluent Bit allows to deliver your collected and processed Events to one or multiple destinations, this is done through a routing phase. A Match represent a simple rule to select Events where it Tags matches a defined rule.

Structured Messages

Source events can have or not have a structure. A structure defines a set of keys and values inside the Event message. As an example consider the following two messages:

No structured message

Structured Message

At a low level both are just an array of bytes, but the Structured message defines keys and values, having a structure helps to implement faster operations on data modifications.

provides different Input Plugins to gather information from different sources, some of them just collect data from log files while others can gather metrics information from the operating system. There are many plugins for different needs.

When an input plugin is loaded, an internal instance is created. Every instance has its own and independent configuration. Configuration keys are often called properties.

Every input plugin has its own documentation section where it's specified how it can be used and what properties are available.

When Fluent Bit processes data, it uses the system memory (heap) as a primary and temporal place to store the record logs before they get delivered, on this private memory area the records are processed.

Buffering refers to the ability to store the records somewhere, and while they are processed and delivered, still be able to store more. Buffering in memory is the fastest mechanism, but there are certain scenarios where the mechanism requires special strategies to deal with backpressure, data safety or reduce memory consumption by the service in constraint environments.

Fluent Bit as buffering strategies, offers a primary buffering mechanism in memory and an optional secondary one using the file system. With this hybrid solution you can adjust to any use case safety and keep a high performance while processing your data.

Both mechanisms are not exclusive and when the data is ready to be processed or delivered it will be always in memory, while other data in the queue might be in the file system until is ready to be processed and moved up to memory.

To learn more about the buffering configuration in Fluent Bit, please jump to the Buffering & Storage section.

On 2014, the Fluentd team at Treasure Data forecasted the need of a lightweight log processor for constraint environments like Embedded Linux and Gateways, the project aimed to be part of the Fluentd Ecosystem and we called it Fluent Bit, fully open source and available under the terms of the Apache License v2.0.

After the project was around for some time, it got some traction in the Embedded market but we also started getting requests for several features from the Cloud community like more inputs, filters, and outputs. Not so long after that, Fluent Bit becomes one of the preferred solutions to solve the logging challenges in Cloud environments.

Fluent Bit, including it core, plugins and tools are distributed under the terms of the Apache License v2.0:

                                 Apache License
                           Version 2.0, January 2004
                        http://www.apache.org/licenses/

   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION

   1. Definitions.

      "License" shall mean the terms and conditions for use, reproduction,
      and distribution as defined by Sections 1 through 9 of this document.

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the
      direction or management of such entity, whether by contract or
      otherwise, or (ii) ownership of fifty percent (50%) or more of the
      outstanding shares, or (iii) beneficial ownership of such entity.

      "You" (or "Your") shall mean an individual or Legal Entity
      exercising permissions granted by this License.

      "Source" form shall mean the preferred form for making modifications,
      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical
      transformation or translation of a Source form, including but
      not limited to compiled object code, generated documentation,
      and conversions to other media types.

      "Work" shall mean the work of authorship, whether in Source or
      Object form, made available under the License, as indicated by a
      copyright notice that is included in or attached to the work
      (an example is provided in the Appendix below).

      "Derivative Works" shall mean any work, whether in Source or Object
      form, that is based on (or derived from) the Work and for which the
      editorial revisions, annotations, elaborations, or other modifications
      represent, as a whole, an original work of authorship. For the purposes
      of this License, Derivative Works shall not include works that remain
      separable from, or merely link (or bind by name) to the interfaces of,
      the Work and Derivative Works thereof.

      "Contribution" shall mean any work of authorship, including
      the original version of the Work and any modifications or additions
      to that Work or Derivative Works thereof, that is intentionally
      submitted to Licensor for inclusion in the Work by the copyright owner
      or by an individual or Legal Entity authorized to submit on behalf of
      the copyright owner. For the purposes of this definition, "submitted"
      means any form of electronic, verbal, or written communication sent
      to the Licensor or its representatives, including but not limited to
      communication on electronic mailing lists, source code control systems,
      and issue tracking systems that are managed by, or on behalf of, the
      Licensor for the purpose of discussing and improving the Work, but
      excluding communication that is conspicuously marked or otherwise
      designated in writing by the copyright owner as "Not a Contribution."

      "Contributor" shall mean Licensor and any individual or Legal Entity
      on behalf of whom a Contribution has been received by Licensor and
      subsequently incorporated within the Work.

   2. Grant of Copyright License. Subject to the terms and conditions of
      this License, each Contributor hereby grants to You a perpetual,
      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
      copyright license to reproduce, prepare Derivative Works of,
      publicly display, publicly perform, sublicense, and distribute the
      Work and such Derivative Works in Source or Object form.

   3. Grant of Patent License. Subject to the terms and conditions of
      this License, each Contributor hereby grants to You a perpetual,
      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
      (except as stated in this section) patent license to make, have made,
      use, offer to sell, sell, import, and otherwise transfer the Work,
      where such license applies only to those patent claims licensable
      by such Contributor that are necessarily infringed by their
      Contribution(s) alone or by combination of their Contribution(s)
      with the Work to which such Contribution(s) was submitted. If You
      institute patent litigation against any entity (including a
      cross-claim or counterclaim in a lawsuit) alleging that the Work
      or a Contribution incorporated within the Work constitutes direct
      or contributory patent infringement, then any patent licenses
      granted to You under this License for that Work shall terminate
      as of the date such litigation is filed.

   4. Redistribution. You may reproduce and distribute copies of the
      Work or Derivative Works thereof in any medium, with or without
      modifications, and in Source or Object form, provided that You
      meet the following conditions:

      (a) You must give any other recipients of the Work or
          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,
          excluding those notices that do not pertain to any part of
          the Derivative Works; and

      (d) If the Work includes a "NOTICE" text file as part of its
          distribution, then any Derivative Works that You distribute must
          include a readable copy of the attribution notices contained
          within such NOTICE file, excluding those notices that do not
          pertain to any part of the Derivative Works, in at least one
          of the following places: within a NOTICE text file distributed
          as part of the Derivative Works; within the Source form or
          documentation, if provided along with the Derivative Works; or,
          within a display generated by the Derivative Works, if and
          wherever such third-party notices normally appear. The contents
          of the NOTICE file are for informational purposes only and
          do not modify the License. You may add Your own attribution
          notices within Derivative Works that You distribute, alongside
          or as an addendum to the NOTICE text from the Work, provided
          that such additional attribution notices cannot be construed
          as modifying the License.

      You may add Your own copyright statement to Your modifications and
      may provide additional or different license terms and conditions
      for use, reproduction, or distribution of Your modifications, or
      for any such Derivative Works as a whole, provided Your use,
      reproduction, and distribution of the Work otherwise complies with
      the conditions stated in this License.

   5. Submission of Contributions. Unless You explicitly state otherwise,
      any Contribution intentionally submitted for inclusion in the Work
      by You to the Licensor shall be under the terms and conditions of
      this License, without any additional terms or conditions.
      Notwithstanding the above, nothing herein shall supersede or modify
      the terms of any separate license agreement you may have executed
      with Licensor regarding such Contributions.

   6. Trademarks. This License does not grant permission to use the trade
      names, trademarks, service marks, or product names of the Licensor,
      except as required for reasonable and customary use in describing the
      origin of the Work and reproducing the content of the NOTICE file.

   7. Disclaimer of Warranty. Unless required by applicable law or
      agreed to in writing, Licensor provides the Work (and each
      Contributor provides its Contributions) on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
      implied, including, without limitation, any warranties or conditions
      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
      PARTICULAR PURPOSE. You are solely responsible for determining the
      appropriateness of using or redistributing the Work and assume any
      risks associated with Your exercise of permissions under this License.

   8. Limitation of Liability. In no event and under no legal theory,
      whether in tort (including negligence), contract, or otherwise,
      unless required by applicable law (such as deliberate and grossly
      negligent acts) or agreed to in writing, shall any Contributor be
      liable to You for damages, including any direct, indirect, special,
      incidental, or consequential damages of any character arising as a
      result of this License or out of the use or inability to use the
      Work (including but not limited to damages for loss of goodwill,
      work stoppage, computer failure or malfunction, or any and all
      other commercial damages or losses), even if such Contributor
      has been advised of the possibility of such damages.

   9. Accepting Warranty or Additional Liability. While redistributing
      the Work or Derivative Works thereof, You may choose to offer,
      and charge a fee for, acceptance of support, warranty, indemnity,
      or other liability obligations and/or rights consistent with this
      License. However, in accepting such obligations, You may act only
      on Your own behalf and on Your sole responsibility, not on behalf
      of any other Contributor, and only if You agree to indemnify,
      defend, and hold each Contributor harmless for any liability
      incurred by, or claims asserted against, such Contributor by reason
      of your accepting any such warranty or additional liability.

   END OF TERMS AND CONDITIONS

Previously defined in the Buffering concept section, the buffer phase in the pipeline aims to provide a unified and persistent mechanism to store your data, either using the primary in-memory model or using the filesystem based mode.

The buffer phase already contains the data in an immutable state, meaning, no other filter can be applied.

Fluent Bit offers a buffering mechanism in the file system that acts as a backup system to avoid data loss in case of system failures.

Fluent Bit is a Fast and Lightweight Log Processor, Stream Processor and Forwarder for Linux, OSX, Windows and BSD family operating systems. It has been made with a strong focus on performance to allow the collection of events from different sources without complexity.

Features

• High Performance

• Data Parsing

  • Convert your unstructured messages using our parsers: JSON, Regex, LTSV and Logfmt

• Reliability and Data Integrity

  • Backpressure Handling

  • Data Buffering in memory and file system

• Networking

  • Security: built-in TLS/SSL support

  • Asynchronous I/O

• Pluggable Architecture and Extensibility: Inputs, Filters and Outputs

  • More than 50 built-in plugins available

  • Extensibility

    • Write any input, filter or output plugin in C language

    • Bonus: write Filters in Lua or Output plugins in Golang

• Monitoring: expose internal metrics over HTTP in JSON and Prometheus format

• Stream Processing: Perform data selection and transformation using simple SQL queries

  • Create new streams of data using query results

  • Aggregation Windows

  • Data analysis and prediction: Timeseries forecasting

• Portable: runs on Linux, MacOS, Windows and BSD systems

Fluent Bit, Fluentd and CNCF

Fluent Bit is a sub-component of the Fluentd project ecosystem, it's licensed under the terms of the Apache License v2.0. This project was created by Treasure Data and is its current primary sponsor.

Nowadays Fluent Bit get contributions from several companies and individuals and same as Fluentd, it's hosted as a CNCF subproject.

Dealing with raw strings or unstructured messages is a constant pain; having a structure is highly desired. Ideally we want to set a structure to the incoming data by the Input Plugins as soon as they are collected:

The Parser allows you to convert from unstructured to structured data. As a demonstrative example consider the following Apache (HTTP Server) log entry:

192.168.2.20 - - [28/Jul/2006:10:27:10 -0300] "GET /cgi-bin/try/ HTTP/1.0" 200 3395

The above log line is a raw string without format, ideally we would like to give it a structure that can be processed later easily. If the proper configuration is used, the log entry could be converted to:

{
  "host":    "192.168.2.20",
  "user":    "-",
  "method":  "GET",
  "path":    "/cgi-bin/try/",
  "code":    "200",
  "size":    "3395",
  "referer": "",
  "agent":   ""
 }

Parsers are fully configurable and are independently and optionally handled by each input plugin, for more details please refer to the Parsers section.

The following article cover the relevant notes for users upgrading from previous Fluent Bit versions. We aim to cover compatibility changes that you must be aware of.

For more details about changes on each release please refer to the .

Fluent Bit v1.5

The migration from v1.4 to v1.5 is pretty straightforward.

• If you enabled keepalive mode in your configuration, note that this configuration property has been renamed to net.keepalive. Now all Network I/O keepalive is enabled by default, to learn more about this and other associated configuration properties read the section.

• If you use the Elasticsearch output plugin, note the default value of type . Many versions of Elasticsearch will tolerate this, but ES v5.6 through v6.1 require a type without a leading underscore. See the for more.

Fluent Bit v1.4

If you are migrating from Fluent Bit v1.3, there are no breaking changes. Just new exciting features to enjoy :)

Fluent Bit v1.3

If you are migrating from Fluent Bit v1.2 to v1.3, there are no breaking changes. If you are upgrading from an older version please review the incremental changes below.

Fluent Bit v1.2

Docker, JSON, Parsers and Decoders

On Fluent Bit v1.2 we have fixed many issues associated with JSON encoding and decoding, for hence when parsing Docker logs is no longer necessary to use decoders. The new Docker parser looks like this:

Note: again, do not use decoders.

Kubernetes Filter

We have done improvements also on how Kubernetes Filter handle the stringified log message. If the option Merge_Log is enabled, it will try to handle the log content as a JSON map, if so, it will add the keys to the root map.

In addition, we have fixed and improved the option called Merge_Log_Key. If a merge log succeed, all new keys will be packaged under the key specified by this option, a suggested configuration is as follows:

As an example, if the original log content is the following map:

the final record will be composed as follows:

Fluent Bit v1.1

If you are upgrading from Fluent Bit <= 1.0.x you should take in consideration the following relevant changes when switching to Fluent Bit v1.1 series:

Kubernetes Filter

We introduced a new configuration property called Kube_Tag_Prefix to help Tag prefix resolution and address an unexpected behavior that landed in previous versions.

During 1.0.x release cycle, a commit in Tail input plugin changed the default behavior on how the Tag was composed when using the wildcard for expansion generating breaking compatibility with other services. Consider the following configuration example:

The expected behavior is that Tag will be expanded to:

but the change introduced in 1.0 series switched from absolute path to the base file name only:

On Fluent Bit v1.1 release we restored to our default behavior and now the Tag is composed using the absolute path of the monitored file.

Having absolute path in the Tag is relevant for routing and flexible configuration where it also helps to keep compatibility with Fluentd behavior.

This behavior switch in Tail input plugin affects how Filter Kubernetes operates. As you know when the filter is used it needs to perform local metadata lookup that comes from the file names when using Tail as a source. Now with the new Kube_Tag_Prefix option you can specify what's the prefix used in Tail input plugin, for the configuration example above the new configuration will look as follows:

So the proper for Kube_Tag_Prefix value must be composed by Tag prefix set in Tail input plugin plus the converted monitored directory replacing slashes with dots.

uses very low CPU and Memory consumption, it's compatible with most of x86, x86_64, arm32v7 and arm64v8 based platforms. In order to build it you need the following components in your system for the build process:

• Compiler: GCC or clang

• CMake

• Flex & Bison: only if you enable the Stream Processor or Record Accessor feature (both enabled by default)

In the core there are not other dependencies, For certain features that depends on third party components like output plugins with special backend libraries (e.g: kafka), those are included in the main source code repository.

The following operating systems and architectures are supported in Fluent Bit.

From an architecture support perspective, Fluent Bit is fully functional on x86_64, Arm64v8 and Arm32v7 based processors.

Fluent Bit can work also on OSX and *BSD systems, but not all plugins will be available on all platforms. Official support will be expanding based on community demand.

Fluent Bit is distributed as td-agent-bit package and is available for the latest (and old) stable Debian systems: Buster, Stretch and Jessie.

Server GPG key

The first step is to add our server GPG key to your keyring, on that way you can get our signed packages:

$ wget -qO - https://packages.fluentbit.io/fluentbit.key | sudo apt-key add -

Update your sources lists

On Debian, you need to add our APT server entry to your sources lists, please add the following content at bottom of your /etc/apt/sources.list file:

Debian 10 (Buster)

deb https://packages.fluentbit.io/debian/buster buster main

Debian 9 (Stretch)

deb https://packages.fluentbit.io/debian/stretch stretch main

Debian 8 (Jessie)

deb https://packages.fluentbit.io/debian/jessie jessie main

Update your repositories database

Now let your system update the apt database:

$ sudo apt-get update

Install TD Agent Bit

Using the following apt-get command you are able now to install the latest td-agent-bit:

$ sudo apt-get install td-agent-bit

Now the following step is to instruct systemd to enable the service:

$ sudo service td-agent-bit start

If you do a status check, you should see a similar output like this:

sudo service td-agent-bit status
● td-agent-bit.service - TD Agent Bit
   Loaded: loaded (/lib/systemd/system/td-agent-bit.service; disabled; vendor preset: enabled)
   Active: active (running) since mié 2016-07-06 16:58:25 CST; 2h 45min ago
 Main PID: 6739 (td-agent-bit)
    Tasks: 1
   Memory: 656.0K
      CPU: 1.393s
   CGroup: /system.slice/td-agent-bit.service
           └─6739 /opt/td-agent-bit/bin/td-agent-bit -c /etc/td-agent-bit/td-agent-bit.conf
...

The default configuration of td-agent-bit is collecting metrics of CPU usage and sending the records to the standard output, you can see the outgoing data in your /var/log/syslog file.

Learn how to install Fluent Bit and the AWS output plugins on Amazon Linux 2 via AWS Systems Manager.

AWS maintains a distribution of Fluent Bit combining the latest official release with a set of Go Plugins for sending logs to AWS services. AWS and Fluent Bit are working together to rewrite their plugins for inclusion in the official Fluent Bit distribution.

Plugins

Currently, the AWS for Fluent Bit image contains Go Plugins for:

• Amazon CloudWatch Logs

• Amazon Kinesis Firehose

• Amazon Kinesis Streams

Versions and Regional Repositories

AWS vends their container image via Docker Hub, and a set of highly available regional Amazon ECR repositories. For more information, see the AWS for Fluent Bit GitHub repo.

The AWS for Fluent Bit image uses a custom versioning scheme because it contains multiple projects. To see what each release contains, check out the release notes on GitHub.

SSM Public Parameters

AWS vends SSM Public Parameters with the regional repository link for each image. These parameters can be queried by any AWS account.

To see a list of available version tags in a given region, run the following command:

aws ssm get-parameters-by-path --region eu-central-1 --path /aws/service/aws-for-fluent-bit/ --query 'Parameters[*].Name'

To see the ECR repository URI for a given image tag in a given region, run the following:

$ aws ssm get-parameter --region ap-northeast-1 --name /aws/service/aws-for-fluent-bit/2.0.0

You can use these SSM public parameters as parameters in your CloudFormation templates:

Parameters:
  FireLensImage:
    Description: Fluent Bit image for the FireLens Container
    Type: AWS::SSM::Parameter::Value<String>
    Default: /aws/service/aws-for-fluent-bit/latest

Fluent Bit uses CMake as it build system. The suggested procedure to prepare the build system consists on the following steps:

Prepare environment

In the following steps you can find exact commands to build and install the project with the default options. If you already know how CMake works you can skip this part and look at the build options available. Note that Fluent Bit requires CMake 3.x. You may need to use cmake3 instead of cmake to complete the following steps on your system.

Change to the build/ directory inside the Fluent Bit sources:

$ cd build/

Let CMake configure the project specifying where the root path is located:

$ cmake ../
-- The C compiler identification is GNU 4.9.2
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- The CXX compiler identification is GNU 4.9.2
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
...
-- Could NOT find Doxygen (missing:  DOXYGEN_EXECUTABLE)
-- Looking for accept4
-- Looking for accept4 - not found
-- Configuring done
-- Generating done
-- Build files have been written to: /home/edsiper/coding/fluent-bit/build

Now you are ready to start the compilation process through the simple make command:

$ make
Scanning dependencies of target msgpack
[  2%] Building C object lib/msgpack-1.1.0/CMakeFiles/msgpack.dir/src/unpack.c.o
[  4%] Building C object lib/msgpack-1.1.0/CMakeFiles/msgpack.dir/src/objectc.c.o
[  7%] Building C object lib/msgpack-1.1.0/CMakeFiles/msgpack.dir/src/version.c.o
...
[ 19%] Building C object lib/monkey/mk_core/CMakeFiles/mk_core.dir/mk_file.c.o
[ 21%] Building C object lib/monkey/mk_core/CMakeFiles/mk_core.dir/mk_rconf.c.o
[ 23%] Building C object lib/monkey/mk_core/CMakeFiles/mk_core.dir/mk_string.c.o
...
Scanning dependencies of target fluent-bit-static
[ 66%] Building C object src/CMakeFiles/fluent-bit-static.dir/flb_pack.c.o
[ 69%] Building C object src/CMakeFiles/fluent-bit-static.dir/flb_input.c.o
[ 71%] Building C object src/CMakeFiles/fluent-bit-static.dir/flb_output.c.o
...
Linking C executable ../bin/fluent-bit
[100%] Built target fluent-bit-bin

to continue installing the binary on the system just do:

$ make install

it's likely you may need root privileges so you can try to prefixing the command with sudo.

Build Options

Fluent Bit provides certain options to CMake that can be enabled or disabled when configuring, please refer to the following tables under the General Options, Development Options, Input Plugins and _Output Plugins sections.

General Options

Development Options

Input Plugins

The input plugins provides certain features to gather information from a specific source type which can be a network interface, some built-in metric or through a specific input device, the following input plugins are available:

Filter Plugins

The filter plugins allows to modify, enrich or drop records. The following table describes the filters available on this version:

Output Plugins

The output plugins gives the capacity to flush the information to some external interface, service or terminal, the following table describes the output plugins available as of this version:

The output interface allows us to define destinations for the data. Common destinations are remote services, local file system or standard interface with others. Outputs are implemented as plugins and there are many available.

When an output plugin is loaded, an internal instance is created. Every instance has its own independent configuration. Configuration keys are often called properties.

Every output plugin has its own documentation section specifying how it can be used and what properties are available.

For more details, please refer to the Output Plugins section.

Routing is a core feature that allows to route your data through Filters and finally to one or multiple destinations. The router relies on the concept of Tags and Matching rules

There are two important concepts in Routing:

• Tag

• Match

When the data is generated by the input plugins, it comes with a Tag (most of the time the Tag is configured manually), the Tag is a human-readable indicator that helps to identify the data source.

In order to define where the data should be routed, a Match rule must be specified in the output configuration.

Consider the following configuration example that aims to deliver CPU metrics to an Elasticsearch database and Memory metrics to the standard output interface:

[INPUT]
    Name cpu
    Tag  my_cpu

[INPUT]
    Name mem
    Tag  my_mem

[OUTPUT]
    Name   es
    Match  my_cpu

[OUTPUT]
    Name   stdout
    Match  my_mem

Note: the above is a simple example demonstrating how Routing is configured.

Routing works automatically reading the Input Tags and the Output Match rules. If some data has a Tag that doesn't match upon routing time, the data is deleted.

Routing with Wildcard

Routing is flexible enough to support wildcard in the Match pattern. The below example defines a common destination for both sources of data:

[INPUT]
    Name cpu
    Tag  my_cpu

[INPUT]
    Name mem
    Tag  my_mem

[OUTPUT]
    Name   stdout
    Match  my_*

The match rule is set to my_* which means it will match any Tag that starts with my_.

Stable

For production systems, we strongly suggest that you always get the latest stable release from our web site, you can get the official tarballs (.tar.gz) from the following link:

https://fluentbit.io/download/

Development

For people who aims to contribute to the project testing or extending the code base, can get the development version from our GIT repository:

$ git clone https://github.com/fluent/fluent-bit

Note that our master branch is where the development of Fluent Bit happens. Since it's a development version, expect issues when compiling or at run time.

We encourage everybody to help us testing every development version, at the end this is what will become stable.

Install on Redhat / CentOS

Fluent Bit is distributed as td-agent-bit package and is available for the latest stable CentOS system. The following architectures are supported

• x86_64

• aarch64 / arm64v8

Configure Yum

We provide td-agent-bit through a Yum repository. In order to add the repository reference to your system, please add a new file called td-agent-bit.repo in /etc/yum.repos.d/ with the following content:

[td-agent-bit]
name = TD Agent Bit
baseurl = https://packages.fluentbit.io/centos/7/$basearch/
gpgcheck=1
gpgkey=https://packages.fluentbit.io/fluentbit.key
enabled=1

note: we encourage you always enable the gpgcheck for security reasons. All our packages are signed.

The GPG Key fingerprint is F209 D876 2A60 CD49 E680 633B 4FF8 368B 6EA0 722A

Install

Once your repository is configured, run the following command to install it:

$ yum install td-agent-bit

Now the following step is to instruct Systemd to enable the service:

$ sudo service td-agent-bit start

If you do a status check, you should see a similar output like this:

$ service td-agent-bit status
Redirecting to /bin/systemctl status  td-agent-bit.service
● td-agent-bit.service - TD Agent Bit
   Loaded: loaded (/usr/lib/systemd/system/td-agent-bit.service; disabled; vendor preset: disabled)
   Active: active (running) since Thu 2016-07-07 02:08:01 BST; 9s ago
 Main PID: 3820 (td-agent-bit)
   CGroup: /system.slice/td-agent-bit.service
           └─3820 /opt/td-agent-bit/bin/td-agent-bit -c etc/td-agent-bit/td-agent-bit.conf
...

The default configuration of td-agent-bit is collecting metrics of CPU usage and sending the records to the standard output, you can see the outgoing data in your /var/log/messages file.

Install on Amazon Linux 2

Fluent Bit is distributed as td-agent-bit package and is available for the latest Amazon Linux 2. The following architectures are supported

• x86_64

• aarch64 / arm64v8

Configure Yum

We provide td-agent-bit through a Yum repository. In order to add the repository reference to your system, please add a new file called td-agent-bit.repo in /etc/yum.repos.d/ with the following content:

[td-agent-bit]
name = TD Agent Bit
baseurl = https://packages.fluentbit.io/amazonlinux/2/$basearch/
gpgcheck=1
gpgkey=https://packages.fluentbit.io/fluentbit.key
enabled=1

note: we encourage you always enable the gpgcheck for security reasons. All our packages are signed.

The GPG Key fingerprint is F209 D876 2A60 CD49 E680 633B 4FF8 368B 6EA0 722A

Install

Once your repository is configured, run the following command to install it:

$ yum install td-agent-bit

Now the following step is to instruct systemd to enable the service:

$ sudo service td-agent-bit start

If you do a status check, you should see a similar output like this:

$ service td-agent-bit status
Redirecting to /bin/systemctl status  td-agent-bit.service
● td-agent-bit.service - TD Agent Bit
   Loaded: loaded (/usr/lib/systemd/system/td-agent-bit.service; disabled; vendor preset: disabled)
   Active: active (running) since Thu 2016-07-07 02:08:01 BST; 9s ago
 Main PID: 3820 (td-agent-bit)
   CGroup: /system.slice/td-agent-bit.service
           └─3820 /opt/td-agent-bit/bin/td-agent-bit -c etc/td-agent-bit/td-agent-bit.conf
...

The default configuration of td-agent-bit is collecting metrics of CPU usage and sending the records to the standard output, you can see the outgoing data in your /var/log/messages file.

Fluent Bit in normal operation mode allows to be configurable through text files or using specific arguments in the command line, while this is the ideal deployment case, there are scenarios where a more restricted configuration is required: static configuration mode.

Static configuration mode aims to include a built-in configuration in the final binary of Fluent Bit, disabling the usage of external files or flags at runtime.

Getting Started

Requirements

The following steps assumes you are familiar with configuring Fluent Bit using text files and you have experience building it from scratch as described in the Build and Install section.

Configuration Directory

In your file system prepare a specific directory that will be used as an entry point for the build system to lookup and parse the configuration files. It is mandatory that this directory contain as a minimum one configuration file called fluent-bit.conf containing the required SERVICE, INPUT and OUTPUT sections. As an example create a new fluent-bit.conf file with the following content:

[SERVICE]
    Flush     1
    Daemon    off
    Log_Level info

[INPUT]
    Name      cpu

[OUTPUT]
    Name      stdout
    Match     *

the configuration provided above will calculate CPU metrics from the running system and print them to the standard output interface.

Build with Custom Configuration

Inside Fluent Bit source code, get into the build/ directory and run CMake appending the FLB_STATIC_CONF option pointing the configuration directory recently created, e.g:

$ cd fluent-bit/build/
$ cmake -DFLB_STATIC_CONF=/path/to/my/confdir/

then build it:

$ make

At this point the fluent-bit binary generated is ready to run without necessity of further configuration:

$ bin/fluent-bit 
Fluent-Bit v0.15.0
Copyright (C) Treasure Data

[2018/10/19 15:32:31] [ info] [engine] started (pid=15186)
[0] cpu.local: [1539984752.000347547, {"cpu_p"=>0.750000, "user_p"=>0.500000, "system_p"=>0.250000, "cpu0.p_cpu"=>1.000000, "cpu0.p_user"=>1.000000, "cpu0.p_system"=>0.000000, "cpu1.p_cpu"=>0.000000, "cpu1.p_user"=>0.000000, "cpu1.p_system"=>0.000000, "cpu2.p_cpu"=>0.000000, "cpu2.p_user"=>0.000000, "cpu2.p_system"=>0.000000, "cpu3.p_cpu"=>1.000000, "cpu3.p_user"=>1.000000, "cpu3.p_system"=>0.000000}]

Fluent Bit is distributed as td-agent-bit package and is available for the latest stable Ubuntu system: Focal Fossa.

Server GPG key

The first step is to add our server GPG key to your keyring, on that way you can get our signed packages:

$ wget -qO - https://packages.fluentbit.io/fluentbit.key | sudo apt-key add -

Update your sources lists

On Ubuntu, you need to add our APT server entry to your sources lists, please add the following content at bottom of your /etc/apt/sources.list file:

Ubuntu 20.04 LTS (Focal Fossa)

deb https://packages.fluentbit.io/ubuntu/focal focal main

Ubuntu 18.04 LTS (Bionic Beaver)

deb https://packages.fluentbit.io/ubuntu/bionic bionic main

Ubuntu 16.04 LTS (Xenial Xerus)

deb https://packages.fluentbit.io/ubuntu/xenial xenial main

Update your repositories database

Now let your system update the apt database:

$ sudo apt-get update

Install TD-Agent Bit

Using the following apt-get command you are able now to install the latest td-agent-bit:

$ sudo apt-get install td-agent-bit

Now the following step is to instruct systemd to enable the service:

$ sudo service td-agent-bit start

If you do a status check, you should see a similar output like this:

sudo service td-agent-bit status
● td-agent-bit.service - TD Agent Bit
   Loaded: loaded (/lib/systemd/system/td-agent-bit.service; disabled; vendor preset: enabled)
   Active: active (running) since mié 2016-07-06 16:58:25 CST; 2h 45min ago
 Main PID: 6739 (td-agent-bit)
    Tasks: 1
   Memory: 656.0K
      CPU: 1.393s
   CGroup: /system.slice/td-agent-bit.service
           └─6739 /opt/td-agent-bit/bin/td-agent-bit -c /etc/td-agent-bit/td-agent-bit.conf
...

The default configuration of td-agent-bit is collecting metrics of CPU usage and sending the records to the standard output, you can see the outgoing data in your /var/log/syslog file.

Fluent Bit container images are available on Docker Hub ready for production usage. Current available images can be deployed in multiple architectures.

Tags and Versions

The following table describe the tags are available on Docker Hub fluent/fluent-bit repository:

It's strongly suggested that you always use the latest image of Fluent Bit.

Multi Architecture Images

Our x86_64 stable image is based in Distroless focusing on security containing just the Fluent Bit binary and minimal system libraries and basic configuration. Optionally, we provide debug images for x86_64 which contains Busybox that can be used to troubleshoot or testing purposes.

In addition, the main manifest provides images for arm64v8 and arm32v7 architectures. From a deployment perspective there is no need to specify an architecture, the container client tool that pulls the image gets the proper layer for the running architecture.

For every architecture we build the layers using the following base images:

Getting Started

Download the last stable image from 1.5 series:

$ docker pull fluent/fluent-bit:1.5

Once the image is in place, now run the following (useless) test which makes Fluent Bit measure CPU usage by the container:

$ docker run -ti fluent/fluent-bit:1.5 /fluent-bit/bin/fluent-bit -i cpu -o stdout -f 1

That command will let Fluent Bit measure CPU usage every second and flush the results to the standard output, e.g:

Fluent-Bit v1.5.x
Copyright (C) Treasure Data

[2019/10/01 12:29:02] [ info] [engine] started
[0] cpu.0: [1504290543.000487750, {"cpu_p"=>0.750000, "user_p"=>0.250000, "system_p"=>0.500000, "cpu0.p_cpu"=>0.000000, "cpu0.p_user"=>0.000000, "cpu0.p_system"=>0.000000, "cpu1.p_cpu"=>1.000000, "cpu1.p_user"=>0.000000, "cpu1.p_system"=>1.000000, "cpu2.p_cpu"=>1.000000, "cpu2.p_user"=>1.000000, "cpu2.p_system"=>0.000000, "cpu3.p_cpu"=>0.000000, "cpu3.p_user"=>0.000000, "cpu3.p_system"=>0.000000}]

F.A.Q

Why there is no Fluent Bit Docker image based on Alpine Linux ?

Alpine Linux uses Musl C library instead of Glibc. Musl is not fully compatible with Glibc which generated many issues in the following areas when used with Fluent Bit:

• Memory Allocator: to run Fluent Bit properly in high-load environments, we use Jemalloc as a default memory allocator which reduce fragmentation and provides better performance for our needs. Jemalloc cannot run smoothly with Musl and requires extra work.

• Alpine Linux Musl functions bootstrap have a compatibility issue when loading Golang shared libraries, this generate problems when trying to load Golang output plugins in Fluent Bit.

• Alpine Linux Musl Time format parser does not support Glibc extensions

• Maintainers preference in terms of base image due to security and maintenance reasons are Distroless and Debian.

Where 'latest' Tag points to ?

Our Docker containers images are deployed thousands of times per day, we take security and stability very seriously.

The latest tag most of the time points to the latest stable image. When we release a major update to Fluent Bit like for example from v1.3.x to v1.4.0, we don't move latest tag until 2 weeks after the release. That give us extra time to verify with our community that everything works as expected.

1# Windows

Fluent Bit is distributed as td-agent-bit package for Windows. Fluent Bit has two flavours of Windows installers: a ZIP archive (for quick testing) and an EXE installer (for system installation).

Installation Packages

The latest stable version is 1.5.7:

To check the integrity, use Get-FileHash commandlet on PowerShell.

PS> Get-FileHash td-agent-bit-1.5.7-win32.exe

Installing from ZIP archive

Download a ZIP archive from the download page. There are installers for 32-bit and 64-bit environments, so choose one suitable for your environment.

Then you need to expand the ZIP archive. You can do this by clicking "Extract All" on Explorer, or if you're using PowerShell, you can use Expand-Archive commandlet.

PS> Expand-Archive td-agent-bit-1.5.7-win64.zip

The ZIP package contains the following set of files.

td-agent-bit
├── bin
│   ├── fluent-bit.dll
│   └── fluent-bit.exe
├── conf
│   ├── fluent-bit.conf
│   ├── parsers.conf
│   └── plugins.conf
└── include
    │   ├── flb_api.h
    │   ├── ...
    │   └── flb_worker.h
    └── fluent-bit.h

Now, launch cmd.exe or PowerShell on your machine, and execute fluent-bit.exe as follows.

PS> .\bin\fluent-bit.exe -i dummy -o stdout

If you see the following output, it's working fine!

PS> .\bin\fluent-bit.exe  -i dummy -o stdout
Fluent Bit v1.5.x
* Copyright (C) 2019-2020 The Fluent Bit Authors
* Copyright (C) 2015-2018 Treasure Data
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2019/06/28 10:13:04] [ info] [storage] initializing...
[2019/06/28 10:13:04] [ info] [storage] in-memory
[2019/06/28 10:13:04] [ info] [storage] normal synchronization mode, checksum disabled, max_chunks_up=128
[2019/06/28 10:13:04] [ info] [engine] started (pid=10324)
[2019/06/28 10:13:04] [ info] [sp] stream processor started
[0] dummy.0: [1561684385.443823800, {"message"=>"dummy"}]
[1] dummy.0: [1561684386.428399000, {"message"=>"dummy"}]
[2] dummy.0: [1561684387.443641900, {"message"=>"dummy"}]
[3] dummy.0: [1561684388.441405800, {"message"=>"dummy"}]

To halt the process, press CTRL-C in the terminal.

Installing from EXE installer

Download an EXE installer from the download page. It has both 32-bit and 64-bit builds. Choose one which is suitable for you.

Then, double-click the EXE installer you've downloaded. Installation wizard will automatically start.

Click Next and proceed. By default, Fluent Bit is installed into C:\Program Files\td-agent-bit\, so you should be able to launch fluent-bit as follow after installation.

PS> C:\Program Files\td-agent-bit\bin\fluent-bit.exe -i dummy -o stdout

Windows Service Support

Windows services are equivalent to "daemons" in UNIX (i.e. long-running background processes). Since v1.5.0, Fluent Bit has the native support for Windows Service.

Suppose you have the following installation layout:

C:\fluent-bit\
├── conf
│   ├── fluent-bit.conf
│   └── parsers.conf
└── bin
    ├── fluent-bit.dll
    └── fluent-bit.exe

To register Fluent Bit as a Windows service, you need to execute the following command on Command Prompt. Please be careful that a single space is required after binpath=.

% sc.exe create fluent-bit binpath= "\fluent-bit\bin\fluent-bit.exe -c \fluent-bit\conf\fluent-bit.conf"

Now Fluent Bit can be started and managed as a normal Windows service.

% sc.exe start fluent-bit
% sc.exe query fluent-bit
SERVICE_NAME: fluent-bit
    TYPE               : 10  WIN32_OWN_PROCESS
    STATE              : 4 Running
    ...

To halt the Fluent Bit service, just execute the "stop" command.

% sc.exe stop fluent-bit

Fluent Bit is a lightweight and extensible Log Processor that comes with full support for Kubernetes:

• Process Kubernetes containers logs from the file system or Systemd/Journald.

• Enrich logs with Kubernetes Metadata.

• Centralize your logs in third party storage services like Elasticsearch, InfluxDB, HTTP, etc.

Concepts

Before getting started it is important to understand how Fluent Bit will be deployed. Kubernetes manages a cluster of nodes, so our log agent tool will need to run on every node to collect logs from every POD, hence Fluent Bit is deployed as a DaemonSet (a POD that runs on every node of the cluster).

When Fluent Bit runs, it will read, parse and filter the logs of every POD and will enrich each entry with the following information (metadata):

• Pod Name

• Pod ID

• Container Name

• Container ID

• Labels

• Annotations

To obtain these information, a built-in filter plugin called kubernetes talks to the Kubernetes API Server to retrieve relevant information such as the pod_id, labels and annotations, other fields such as pod_name, container_id and container_name are retrieved locally from the log file names. All of this is handled automatically, no intervention is required from a configuration aspect.

Our Kubernetes Filter plugin is fully inspired on the Fluentd Kubernetes Metadata Filter written by Jimmi Dyson.

Installation

Fluent Bit must be deployed as a DaemonSet, so on that way it will be available on every node of your Kubernetes cluster. To get started run the following commands to create the namespace, service account and role setup:

$ kubectl create namespace logging
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-service-account.yaml
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-role.yaml
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-role-binding.yaml

The next step is to create a ConfigMap that will be used by our Fluent Bit DaemonSet:

$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-configmap.yaml

Note for Kubernetes < v1.16

For Kubernetes versions olden than v1.16, the DaemonSet resource is not available on apps/v1 , the resource is available on apiVersion: extensions/v1beta1 . Our current Daemonset Yaml files uses the new apiVersion.

If you are using and older Kubernetes, grab manually a copy of your Daemonset Yaml file and replace the value of apiVersion from:

apiVersion: apps/v1

to

apiVersion: extensions/v1beta1

You can read more about this deprecation on Kubernetes v1.14 Changelog here:

https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.14.md#deprecations

Fluent Bit to Elasticsearch

Fluent Bit DaemonSet ready to be used with Elasticsearch on a normal Kubernetes Cluster:

$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-ds.yaml

Fluent Bit to Elasticsearch on Minikube

If you are using Minikube for testing purposes, use the following alternative DaemonSet manifest:

$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-ds-minikube.yaml

Details

The default configuration of Fluent Bit makes sure of the following:

• Consume all containers logs from the running Node.

• The Tail input plugin will not append more than 5MB into the engine until they are flushed to the Elasticsearch backend. This limit aims to provide a workaround for backpressure scenarios.

• The Kubernetes filter will enrich the logs with Kubernetes metadata, specifically labels and annotations. The filter only goes to the API Server when it cannot find the cached info, otherwise it uses the cache.

• The default backend in the configuration is Elasticsearch set by the Elasticsearch Ouput Plugin. It uses the Logstash format to ingest the logs. If you need a different Index and Type, please refer to the plugin option and do your own adjustments.

• There is an option called Retry_Limit set to False, that means if Fluent Bit cannot flush the records to Elasticsearch it will re-try indefinitely until it succeed.

Fluent Bit source code provides Bitbake recipes to configure, build and package the software for a Yocto based image. Note that specific steps of usage of these recipes in your Yocto environment (Poky) is out of the scope of this documentation.

We distribute two main recipes, one for testing/dev purposes and other with the latest stable release.

It's strongly recommended to always use the stable release of Fluent Bit recipe and not the one from GIT master for production deployments.

Fluent Bit and other architectures

Fluent Bit >= v1.1.x fully supports x86_64, x86, arm32v7 and arm64v8.

In production environments we want to have full control of the data we are collecting, filtering is an important feature that allows us to alter the data before delivering it to some destination.

Filtering is implemented through plugins, so each filter available could be used to match, exclude or enrich your logs with some specific metadata.

We support many filters, A common use case for filtering is Kubernetes deployments. Every Pod log needs to get the proper metadata associated

Very similar to the input plugins, Filters run in an instance context, which has its own independent configuration. Configuration keys are often called properties.

For more details about the Filters available and their usage, please refer to the Filters section.

Certain configuration directives in Fluent Bit refer to unit sizes such as when defining the size of a buffer or specific limits, we can find these in plugins like , or in generic properties like .

Starting from v0.11.10, all unit sizes have been standardized across the core and plugins, the following table describes the options that can be used and what they mean:

Fluent Bit is distributed as td-agent-bit package and is available for the Raspberry, specifically for distribution, the following versions are supported:

• Raspbian Buster (10)

• Raspbian Stretch (9)

• Raspbian Jessie (8)

Server GPG key

The first step is to add our server GPG key to your keyring, on that way you can get our signed packages:

Update your sources lists

On Debian and derivated systems such as Raspbian, you need to add our APT server entry to your sources lists, please add the following content at bottom of your /etc/apt/sources.list file:

Raspbian 10 (Buster)

Raspbian 9 (Stretch)

Raspbian 8 (Jessie)

Update your repositories database

Now let your system update the apt database:

Install TD-Agent Bit

Using the following apt-get command you are able now to install the latest td-agent-bit:

Now the following step is to instruct systemd to enable the service:

If you do a status check, you should see a similar output like this:

The default configuration of td-agent-bit is collecting metrics of CPU usage and sending the records to the standard output, you can see the outgoing data in your /var/log/syslog file.

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.

Example

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.

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.

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.

Configuration

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:

Nodes and specific plugin configuration

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).

Nodes and TLS (Transport Layer Security)

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 TLS options available are described in the section and can be added to the any Node section.

Configuration File Example

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.

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:

@INCLUDE Command

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:

inputs.conf

outputs.conf

Note that despites the order of inclusion, Fluent Bit will ALWAYS respect the following order:

• Service

• Inputs

• Filters

• Outputs

@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:

The end-goal of is to collect, parse, filter and ship logs to a central place. In this workflow there are many phases and one of the critical pieces is the ability to do buffering : a mechanism to place processed data into a temporal location until is ready to be shipped.

By default when Fluent Bit process data, it uses Memory as a primary and temporal place to store the record logs, but there are certain scenarios where would be ideal to have a persistent buffering mechanism based in the filesystem to provide aggregation and data safety capabilities.

Starting with Fluent Bit v1.0, we introduced a new storage layer that can either work in memory or in the file system. Input plugins can be configured to use one or the other upon demand at start time.

Configuration

The storage layer configuration takes place in two areas:

• Service Section

• Input Section

The known Service section configure a global environment for the storage layer, and then in the Input sections defines which mechanism to use.

Service Section Configuration

The Service section refers to the section defined in the main :

a Service section will look like this:

that configuration configure an optional buffering mechanism where it root for data is /var/log/flb-storage/, it will use normal synchronization mode, without checksum and up to a maximum of 5MB of memory when processing backlog data.

Input Section Configuration

Optionally, any Input plugin can configure their storage preference, the following table describe the options available:

The following example configure a service that offers filesystem buffering capabilities and two Input plugins being the first based in filesystem and the second with memory only.

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 miscellaneus values.

Format

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.

Usage Example

The file content to process in test.log is the following:

Running Fluent Bit with the configuration above the output will be:

Fluent Bit might optionally use a configuration file to define how the service will behave, and 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:

Sections

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.

Entries: Key/Value

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.

Indented Configuration Mode

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.

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 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

Service

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:

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 its 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).

Example

The following is an example of an INPUT section:

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 its 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.

Example

The following is an example of an FILTER section:

Output

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

Example

The following is an example of an OUTPUT section:

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:

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:

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:

In certain environments is common to see that logs or data being ingested is faster than the ability to flush it to some destinations. The common case is reading from big log files and dispatching the logs to a backend over the network which takes some time to respond, this generate backpressure leading to a high memory consumption in the service.

In order to avoid backpressure, Fluent Bit implements a mechanism in the engine that restrict the amount of data than an input plugin can ingest, this is done through the configuration parameter Mem_Buf_Limit.

Mem_Buf_Limit

This option is disabled by default and can be applied to all input plugins. Let's explain it behavior using the following scenario:

• Mem_Buf_Limit is set to 1MB (one megabyte)

• input plugin tries to append 700KB

• engine route the data to an output plugin

• output plugin backend (HTTP Server) is down

• engine scheduler will retry the flush after 10 seconds

• input plugin tries to append 500KB