MQTT

The MQTT input plugin retrieves messages and data from MQTT control packets over a TCP connection. The incoming data to receive must be a JSON map.

Configuration parameters

The plugin supports the following configuration parameters:

Key	Description	Default
Listen	Listener network interface.	0.0.0.0
Port	TCP port where listening for connections.	1883
Payload_Key	Specify the key where the payload key/value will be preserved.	none
Threaded	Indicates whether to run this input in its own thread.	false

Get started

To listen for MQTT messages, you can run the plugin from the command line or through the configuration file.

Command line

The MQTT input plugin lets Fluent Bit behave as a server. Dispatch some messages using a MQTT client. In the following example, the mosquitto tool is being used for the purpose:

Running the following command:

$ fluent-bit -i mqtt -t data -o stdout -m '*'

Returns a response like the following:

Fluent Bit v4.0.3
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___  _____
|  ___| |                | |   | ___ (_) |           /   ||  _  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| || |/' |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| ||  /| |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |\ |_/ /
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/


[2025/07/01 14:44:47] [ info] [fluent bit] version=4.0.3, commit=f5f5f3c17d, pid=1
[2025/07/01 14:44:47] [ info] [storage] ver=1.5.3, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/07/01 14:44:47] [ info] [simd    ] disabled
[2025/07/01 14:44:47] [ info] [cmetrics] version=1.0.3
[2025/07/01 14:44:47] [ info] [ctraces ] version=0.6.6
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] initializing
[2025/07/01 14:44:47] [ info] [input:mem:mem.0] storage_strategy='memory' (memory only)
[2025/07/01 14:44:47] [ info] [sp] stream processor started
[2025/07/01 14:44:47] [ info] [engine] Shutdown Grace Period=5, Shutdown Input Grace Period=2
[2025/07/01 14:44:47] [ info] [output:stdout:stdout.0] worker #0 started
[0] data: [1463775773, {"topic"=>"some/topic", "key1"=>123, "key2"=>456}]

The following command line will send a message to the MQTT input plugin:

$ mosquitto_pub  -m '{"key1": 123, "key2": 456}' -t some/topic

Configuration file

In your main configuration file append the following:

fluent-bit.yaml

pipeline:
    inputs:
        - name: mqtt
          tag: data
          listen: 0.0.0.0
          port: 1883
          
    outputs:
        - name: stdout
          match: '*'

fluent-bit.conf

[INPUT]
    Name   mqtt
    Tag    data
    Listen 0.0.0.0
    Port   1883

[OUTPUT]
    Name   stdout
    Match  *