UDP

Send logs to a remote UDP server

The UDP output plugin lets you send records to a remote UDP server. The payload can be formatted in different ways as required.

Configuration parameters

This plugin supports the following parameters:

Key	Description	Default
format	Specify the data format to be printed. Supported formats: msgpack, json, json_lines, json_stream.	json_lines
host	Target host where the UDP server is listening.	127.0.0.1
json_date_format	Specify the format of the date. Supported formats: double, epoch, epoch_ms, iso8601, java_sql_timestamp.	double
json_date_key	Specify the name of the time key in the output record. To disable the time key, set the value to false.	date
port	UDP port of the target service.	5170
raw_message_key	Use a raw message key for the message. When set, the plugin sends the value of this key as the raw message instead of formatting it as JSON.	none
workers	The number of workers to perform flush operations for this output.	2

Get started

To send records to a UDP server, you can run the plugin from the command line or through the configuration file.

Command line

The UDP plugin can read the parameters from the command line through the -p argument (property) or by setting them directly through the service URI. The URI format is the following:

udp://host:port

Using the format specified, start Fluent Bit through:

fluent-bit -i cpu -t cpu -o udp://192.168.2.3:5170 -p format=json_lines -v

which is similar to:

fluent-bit -i cpu -t cpu -o udp -p host=192.168.2.3 -p port=5170 \
  -p format=json_lines -o stdout -m '*'

Configuration file

In your main configuration file append the following:

fluent-bit.yaml

pipeline:
  inputs:
    - name: cpu
      tag: cpu

  outputs:
    - name: udp
      match: '*'
      host: 192.168.2.3
      port: 5170
      format: json_lines

fluent-bit.conf

[INPUT]
  Name cpu
  Tag  cpu

[OUTPUT]
  Name  udp
  Match *
  Host  192.168.2.3
  Port  5170
  Format json_lines

JSON format examples

JSON lines format

This example sends CPU metrics in JSON lines format to a UDP server:

fluent-bit.yaml

pipeline:
  inputs:
    - name: cpu
      tag: cpu

  outputs:
    - name: udp
      match: '*'
      host: 127.0.0.1
      port: 5170
      format: json_lines
      json_date_key: timestamp
      json_date_format: iso8601

fluent-bit.conf

[INPUT]
  Name cpu
  Tag  cpu

[OUTPUT]
  Name            udp
  Match           *
  Host            127.0.0.1
  Port            5170
  Format          json_lines
  Json_Date_Key   timestamp
  Json_Date_Format iso8601

Run the following in a separate terminal, netcat will start listening for messages on UDP port 5170:

nc -u -l 5170

After Fluent Bit connects, you should see output in JSON format:

{"timestamp":"2024-01-15T10:30:45.123456Z","cpu_p":1.1875,"user_p":0.5625,"system_p":0.625}
{"timestamp":"2024-01-15T10:30:46.123456Z","cpu_p":2.25,"user_p":2.0,"system_p":0.25}

Raw message format

When raw_message_key is set, the plugin sends the value of the specified key as a raw message instead of formatting it as JSON. This is for when you want to send pre-formatted messages:

fluent-bit.yaml

pipeline:
  inputs:
    - name: tail
      path: /var/log/app.log
      tag: app

  outputs:
    - name: udp
      match: '*'
      host: 127.0.0.1
      port: 5170
      raw_message_key: message

fluent-bit.conf

[INPUT]
  Name tail
  Path /var/log/app.log
  Tag  app

[OUTPUT]
  Name           udp
  Match          *
  Host           127.0.0.1
  Port           5170
  Raw_Message_Key message

Message size limitations

UDP has a maximum datagram size of 65535 bytes. If a record exceeds this size, the plugin will send it but log a debug message. For large messages, consider using TCP or HTTP output plugins instead.

Testing

To test the UDP output plugin, you can use netcat to listen for incoming UDP messages:

nc -u -l 5170

Or use socat for more advanced testing:

socat UDP-RECV:5170 STDOUT