The websocket output plugin allows to flush your records into a WebSocket endpoint. For now the functionality is pretty basic and it issues a HTTP GET request to do the handshake, and then use TCP connections to send the data records in either JSON or MessagePack (or JSON) format.

Configuration Parameters





IP address or hostname of the target WebScoket Server


TCP port of the target WebScoket Server



Specify an optional HTTP URI for the target websocket server, e.g: /something



Specify the data format to be used in the HTTP request body, by default it uses msgpack. Other supported formats are json, json_stream and json_lines and gelf.



Specify the name of the date field in output



Specify the format of the date. Supported formats are double and iso8601 (eg: 2018-05-30T09:39:52.000681Z)



The interval that websocket output plugin would keep to decide if it is OK to reconnect to Websocket Server


Getting Started

In order to insert records into a HTTP server, you can run the plugin from the command line or through the configuration file:

Command Line

The websocket plugin, can read the parameters from the command line in two ways, through the -p argument (property) or setting them directly through the service URI. The URI format is the following:


Using the format specified, you could start Fluent Bit through:

$ fluent-bit -i cpu -t cpu -o websocket:// -m '*'

Configuration File

In your main configuration file, append the following Input & Output sections:

Name cpu
Tag cpu
Name websocket
Match *
Port 80
URI /something
Format json
Idle_interval 21

Suggested configuration for Idle Interval is 20. Websocket plugin is working with tcp keepalive mode, please refer to networking section for details.

By default, if there is no traffic for about 30 seconds, fluent-bit would abort the tcp connection. As a result, if websocket would like to send data to the same server again, it has to reconnect. This parameter is to help to determine if websocket need to reconnect or not.


Configuration File

Name tcp
Port 5170
Format json
Name websocket
Match *
Port 9000
Format json
Idle_interval 21

Once Fluent Bit is running, you can send some messages using the netcat:

$ echo '{"key 1": 123456789, "key 2": "abcdefg"}' | nc 5170; sleep 35; echo '{"key 1": 123456789, "key 2": "abcdefg"}' | nc 5170

In Fluent Bit we should see the following output:

bin/fluent-bit -c ../conf/out_ws.conf
Fluent Bit v1.5.0
* 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
[2020/07/07 03:39:31] [ info] [storage] version=1.0.4, initializing...
[2020/07/07 03:39:31] [ info] [storage] in-memory
[2020/07/07 03:39:31] [ info] [storage] normal synchronization mode, checksum disabled, max_chunks_up=128
[2020/07/07 03:39:31] [ info] [engine] started (pid=12734)
[2020/07/07 03:39:31] [ info] [input:tcp:tcp.0] listening on
[2020/07/07 03:39:31] [ info] [out_ws] we have following parameter /,, 9000, 22
[2020/07/07 03:39:31] [ info] [sp] stream processor started
[2020/07/07 03:39:36] [ info] [out_ws] handshake for ws
[2020/07/07 03:40:11] [ warn] [engine] failed to flush chunk '12734-1594107609.72852130.flb', retry in 6 seconds: task_id=0, input=tcp.0 > output=websocket.0
[2020/07/07 03:40:17] [ info] [out_ws] handshake for ws
[2020/07/07 03:40:17] [ info] [engine] flush chunk '12734-1594107609.72852130.flb' succeeded at retry 1: task_id=1, input=tcp.0 > output=websocket.0

Scenario Description

From the output of fluent-bit log, we see that once data has been ingested into fluent bit, plugin would perform handshake. After a while, no data or traffic is undergoing, tcp connection has been abort. And then another piece of data arrived, a try fro websocket plugin has been triggered, following with another handshake and data flush.