Syslog

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

As of Fluent Bit v1.5.3 the configuration is very strict. You must be aware of the structure of your original record so you can configure the plugin to use specific keys to compose your outgoing Syslog message.

Future versions of Fluent Bit are expanding this plugin feature set to support better handling of keys and message composing.

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, tls 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. rfc3164 sets max size to 1024 bytes. rfc5424 sets the size to 2048 bytes.
syslog_severity_key	The key name from the original record that contains the Syslog severity number. This configuration is optional.
syslog_severity_preset	The preset severity number. It will be overwritten if syslog_severity_key is set and a key of a record is matched. This configuration is optional.	6
syslog_facility_key	The key name from the original record that contains the Syslog facility number. This configuration is optional.
syslog_facility_preset	The preset facility number. It will be overwritten if syslog_facility_key is set and a key of a record is matched. This configuration is optional.	1
syslog_hostname_key	The key name from the original record that contains the hostname that generated the message. This configuration is optional.
syslog_hostname_preset	The preset hostname. It will be overwritten if syslog_hostname_key is set and a key of a record is matched. This configuration is optional.
syslog_appname_key	The key name from the original record that contains the application name that generated the message. This configuration is optional.
syslog_appname_preset	The preset application name. It will be overwritten if syslog_appname_key is set and a key of a record is matched. This configuration is optional.
syslog_procid_key	The key name from the original record that contains the Process ID that generated the message. This configuration is optional.
syslog_procid_preset	The preset process ID. It will be overwritten if syslog_procid_key is set and a key of a record is matched. This configuration is optional.
syslog_msgid_key	The key name from the original record that contains the Message ID associated to the message. This configuration is optional.
syslog_msgid_preset	The preset message ID. It will be overwritten if syslog_msgid_key is set and a key of a record is matched. This configuration is optional.
syslog_sd_key	The key name from the original record that contains the Structured Data (SD) content. This configuration is optional.
syslog_message_key	The key name from the original record that contains the message to deliver. Note that this property is mandatory, otherwise the message will be empty.
allow_longer_sd_id	If true, Fluent-bit allows SD-ID that is longer than 32 characters. Such long SD-ID violates RFC 5424.	false

Examples

Configuration File

Get started quickly with this configuration file:

[OUTPUT]
    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

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:

[OUTPUT]
    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

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.