WebSocket

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

Key	Description	default
Host	IP address or hostname of the target WebScoket Server	127.0.0.1
Port	TCP port of the target WebScoket Server	80
URI	Specify an optional HTTP URI for the target websocket server, e.g: /something	/
Format	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.	msgpack
json_date_key	Specify the name of the date field in output	date
json_date_format	Specify the format of the date. Supported formats are double, epoch, iso8601 (eg: 2018-05-30T09:39:52.000681Z) and java_sql_timestamp (eg: 2018-05-30 09:39:52.000681)	double

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:

http://host:port/something

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

$ fluent-bit -i cpu -t cpu -o websocket://192.168.2.3:80/something -m '*'

Configuration File

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

[INPUT]
    Name  cpu
    Tag   cpu

[OUTPUT]
    Name  websocket
    Match *
    Host  192.168.2.3
    Port  80
    URI   /something
    Format json

Websocket plugin is working with tcp keepalive mode, please refer to networking section for details. Since websocket is a stateful plugin, it will decide when to send out handshake to server side, for example when plugin just begins to work or after connection with server has been dropped. In general, the interval to init a new websocket handshake would be less than the keepalive interval. With that strategy, it could detect and resume websocket connections.

Testing

Configuration File

[INPUT]
    Name        tcp
    Listen      0.0.0.0
    Port        5170
    Format      json
[OUTPUT]
    Name           websocket
    Match          *
    Host           127.0.0.1
    Port           8080
    URI            /
    Format         json
    workers	   4
    net.keepalive               on
    net.keepalive_idle_timeout  30

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

$ echo '{"key 1": 123456789, "key 2": "abcdefg"}' | nc 127.0.0.1 5170; sleep 35; echo '{"key 1": 123456789, "key 2": "abcdefg"}' | nc 127.0.0.1 5170

In Fluent Bit we should see the following output:

bin/fluent-bit   -c ../conf/out_ws.conf
Fluent Bit v1.7.0
* 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

[2021/02/05 22:17:09] [ info] [engine] started (pid=6056)
[2021/02/05 22:17:09] [ info] [storage] version=1.1.0, initializing...
[2021/02/05 22:17:09] [ info] [storage] in-memory
[2021/02/05 22:17:09] [ info] [storage] normal synchronization mode, checksum disabled, max_chunks_up=128
[2021/02/05 22:17:09] [ info] [input:tcp:tcp.0] listening on 0.0.0.0:5170
[2021/02/05 22:17:09] [ info] [out_ws] we have following parameter /, 127.0.0.1, 8080, 25
[2021/02/05 22:17:09] [ info] [output:websocket:websocket.0] worker #1 started
[2021/02/05 22:17:09] [ info] [output:websocket:websocket.0] worker #0 started
[2021/02/05 22:17:09] [ info] [sp] stream processor started
[2021/02/05 22:17:09] [ info] [output:websocket:websocket.0] worker #3 started
[2021/02/05 22:17:09] [ info] [output:websocket:websocket.0] worker #2 started
[2021/02/05 22:17:33] [ info] [out_ws] handshake for ws
[2021/02/05 22:18:08] [ warn] [engine] failed to flush chunk '6056-1612534687.673438119.flb', retry in 7 seconds: task_id=0, input=tcp.0 > output=websocket.0 (out_id=0)
[2021/02/05 22:18:15] [ info] [out_ws] handshake for ws
^C[2021/02/05 22:18:23] [engine] caught signal (SIGINT)
[2021/02/05 22:18:23] [ warn] [engine] service will stop in 5 seconds
[2021/02/05 22:18:27] [ info] [engine] service stopped
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #0 stopping...
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #0 stopped
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #1 stopping...
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #1 stopped
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #2 stopping...
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #2 stopped
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #3 stopping...
[2021/02/05 22:18:27] [ info] [output:websocket:websocket.0] thread worker #3 stopped
[2021/02/05 22:18:27] [ info] [out_ws] flb_ws_conf_destroy

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 would been abort. And then another piece of data arrived, a retry for websocket plugin has been triggered, with another handshake and data flush.

There is another scenario, once websocket server flaps in a short time, which means it goes down and up in a short time, fluent-bit would resume tcp connection immediately. But in that case, websocket output plugin is a malfunction state, it needs to restart fluent-bit to get back to work.