Syslog

The Syslog output plugin lets you deliver messages to Syslog servers. It supports RFC3164 and RFC5424 formats through different transports such as UDP, TCP, or TLS.

Configuration parameters

Key	Description	Default
host	Domain or IP address of the remote Syslog server.	127.0.0.1
port	TCP or UDP port of the remote Syslog server.	514
mode	Desired transport type. Available options are tcp and udp.	udp
syslog_format	The Syslog protocol format to use. Available options are rfc3164 and rfc5424.	rfc5424
syslog_maxsize	The maximum size allowed per message. The value must be an integer representing the number of bytes allowed. If no value is provided, the default size is set depending of the protocol version specified by syslog_format. The value rfc3164 sets max size to 1024 bytes, and rfc5424 sets the size to 2048 bytes.	none
syslog_severity_key	Optional. The key name from the original record that contains the Syslog severity number.	none
syslog_severity_preset	Optional. The preset severity number. It will be overwritten if syslog_severity_key is set and a key of a record is matched.	6
syslog_facility_key	Optional. The key name from the original record that contains the Syslog facility number.	none
syslog_facility_preset	Optional. The preset facility number. It will be overwritten if syslog_facility_key is set and a key of a record is matched.	1
syslog_hostname_key	Optional. The key name from the original record that contains the hostname that generated the message.	none
syslog_hostname_preset	Optional. The preset hostname. It will be overwritten if syslog_hostname_key is set and a key of a record is matched.	none
syslog_appname_key	Optional. The key name from the original record that contains the application name that generated the message.	none
syslog_appname_preset	Optional. The preset application name. It will be overwritten if syslog_appname_key is set and a key of a record is matched.	none
syslog_procid_key	Optional. The key name from the original record that contains the Process ID that generated the message.	none
syslog_procid_preset	Optional. The preset process ID. It will be overwritten if syslog_procid_key is set and a key of a record is matched.	none
syslog_msgid_key	Optional. The key name from the original record that contains the Message ID associated to the message.	none
syslog_msgid_preset	Optional. The preset message ID. It will be overwritten if syslog_msgid_key is set and a key of a record is matched.	none
syslog_sd_key	Optional. The key name from the original record that contains a map of key/value pairs to use as Structured Data (SD) content. The key name is included in the resulting SD field as shown in the examples in this doc.	none
syslog_message_key	Required. The key name from the original record that contains the message to deliver.	none
allow_longer_sd_id	If true, Fluent Bit allows SD-ID values longer than 32 characters. SD-ID values that exceed 32 characters violate RFC5424 standards.	false
workers	The number of workers to perform flush operations for this output.	0

TLS / SSL

The Syslog output plugin supports TLS/SSL. For more details about the properties available and general configuration, see TLS/SSL.

Examples

Configuration file

Get started quickly with this configuration file:

fluent-bit.yaml

pipeline:

  outputs:
    - name: syslog
      match: "*"
      host: syslog.yourserver.com
      port: 514
      mode: udp
      syslog_format: rfc5424
      syslog_maxsize: 2048
      syslog_severity_key: severity
      syslog_facility_key: facility
      syslog_hostname_key: hostname
      syslog_appname_key: appname
      syslog_procid_key: procid
      syslog_msgid_key: msgid
      syslog_sd_key: sd
      syslog_message_key: message

fluent-bit.conf

Structured data

The following is an example of how to configure the syslog_sd_key to send Structured Data to the remote Syslog server.

Example log:

{
  "hostname": "myhost",
  "appname": "myapp",
  "procid": "1234",
  "msgid": "ID98",
  "uls@0": {
    "logtype": "access",
    "clustername": "mycluster",
    "namespace": "mynamespace"
  },
  "log": "Sample app log message."
}

Example configuration file:

fluent-bit.yaml

pipeline:

  outputs:
    - name: syslog
      match: "*"
      host: syslog.yourserver.com
      port: 514
      mode: udp
      syslog_format: rfc5424
      syslog_maxsize: 2048
      syslog_hostname_key: hostname
      syslog_appname_key: appname
      syslog_procid_key: procid
      syslog_msgid_key: msgid
      syslog_sd_key: uls@0
      syslog_message_key: log

fluent-bit.conf

Example output:

...
<14>1 2021-07-12T14:37:35.569848Z myhost myapp 1234 ID98 [uls@0 logtype="access" clustername="mycluster" namespace="mynamespace"] Sample app log message.
...

Add structured data authentication token

Some services use the structured data field to pass authentication tokens (for example, [<token>@41018]), which would need to be added to each log message dynamically. However, this requires setting the token as a key rather than as a value.

Here's an example of how that might be achieved, using AUTH_TOKEN as a variable:

fluent-bit.yaml

pipeline:

  filters:
    - name:  lua
      match: "*"
      call:  append_token
      code:  |
        function append_token(tag, timestamp, record)
            record["${AUTH_TOKEN}"] = {}
            return 2, timestamp, record
        end

  outputs:
    - name: syslog
      match: "*"
      host: syslog.yourserver.com
      port: 514
      mode: tcp
      syslog_format: rfc5424
      syslog_hostname_preset: myhost
      syslog_appname_preset: myapp
      syslog_message_key: log
      allow_longer_sd_id: true
      syslog_sd_key: ${AUTH_TOKEN}
      tls: on
      tls.crt_file: /path/to/my.crt

fluent-bit.conf