Fluentd
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syslog

The in_syslog Input plugin enables Fluentd to retrieve records via the syslog protocol on UDP or TCP.
It is included in Fluentd's core.

Example Configuration

<source>
@type syslog
port 5140
bind 0.0.0.0
tag system
</source>
This tells Fluentd to create a socket listening on port 5140. You need to set up your syslog daemon to send messages to the socket. For example, if you're using rsyslogd, add the following lines to /etc/rsyslog.conf:
# Send log messages to Fluentd
*.* @127.0.0.1:5140

Example Usage

The retrieved data is organized as follows. Fluentd's tag is generated by the tag parameter (tag prefix), facility level, and priority. The record is parsed by the regexp here.
tag = "#{@tag}.#{facility}.#{priority}"
time = 1353436518,
record = {
"host": "host",
"ident": "ident",
"pid": "12345",
"message": "text"
}
If you want to keep facility and priority in the record, set related parameters.

Plugin Helpers

Parameters

@type (required)

The value must be syslog.

tag (required)

The prefix of the tag. The tag itself is generated by the tag prefix, facility level, and priority.

port

type
default
version
integer
5140
0.14.0
The port to listen to.

bind

type
default
version
string
0.0.0.0 (all addresses)
0.14.0
The bind address to listen to.

protocol_type

type
default
available values
version
enum
udp
udp/tcp
0.14.0
The transport protocol used to receive logs. udp and tcp are supported.
This parameter is deprecated since v1.5. Use <transport> instead.

<transport> Section

type
default
available values
version
enum
udp
udp/tcp/tls
1.5.0
The protocol of the syslog transport.
<source>
@type syslog
tag system
<transport tcp>
</transport>
# other parameters
</source>
See How to Enable TLS Encryption section for how to use and see Configuration Example for all supported parameters.

message_length_limit

type
default
version
size
2048
0.14.2
The maximum length of a syslog message in bytes. If you send a larger message, change this parameter.

frame_type

type
default
available values
version
enum
traditional
traditional/octet_count
1.3.0
Specifies the framing type in TCP protocol.
  • traditional
Messages are delimited by newline():
<6>Sep 10 00:00:00 localhost logger: hello!
  • octet_count
Message has the message size prefix to delimit:
43 <6>Sep 10 00:00:00 localhost logger: hello!
See also RFC 6587.

format

Deprecated parameter. Use <parse> instead.

<parse> Directive

The format of the log. This option is used to parse non-standard syslog formats using parser plugins.
<source>
@type syslog
tag system
<parse>
@type FORMAT_PARAMETER
</parse>
</source>
Your <parse> regexp should not consider the 'priority' prefix of the log. For example, if in_syslog receives the log below:
<1>Feb 20 00:00:00 192.168.0.1 fluentd[11111]: [error] hogehoge
Then, the format parser receives the following log:
Feb 20 00:00:00 192.168.0.1 fluentd[11111]: [error] hogehoge
If the <parse>/@type parameter is missing, the log data is assumed to have the canonical syslog format. It is same with the following configuration:
<parse>
@type syslog
with_priority true
</parse>

message_format

type
default
available values
version
enum
rfc3164
rfc3164/rfc5424/auto
0.14.14
This parameter is used inside <parse> directive. The default is rfc3164.
<source>
@type syslog
tag system
<parse>
message_format rfc5424
</parse>
</source>
Specifies the protocol format. Supported values are rfc3164, rfc5424 and auto. If your syslog uses rfc5424, use rfc5424 instead. Here is an example of message:
# rfc3164
<6>Feb 28 12:00:00 192.168.0.1 fluentd[11111]: [error] Hello!
# rfc5424
<16>1 2017-02-28T12:00:00.009Z 192.168.0.1 fluentd - - - Hello!
auto is useful when in_syslog receives both rfc3164 and rfc5424 message per source. in_syslog detects message format by using message prefix and parses it.

with_priority

type
default
version
bool
true
0.14.0
This parameter is used inside <parse> directive.
<source>
@type syslog
tag system
<parse>
with_priority false
</parse>
</source>
If with_priority is true, then syslog messages are assumed to be prefixed with a priority tag like <3>. This option exists since some syslog daemons output logs without the priority tag preceding the message body.
If you wish to parse syslog messages of arbitrary formats, in_tcp or in_udp are recommended.

emit_unmatched_lines

type
default
version
bool
false
1.6.3
Emits unmatched lines when <parse> format is not matched for incoming logs.
Emitted record is {"unmatched_line" : "incoming line"} with ${tag parameter}.unmatched tag.

resolve_hostname

type
default
version
bool
nil
0.14.19
Tries to resolve hostname from IP addresses or not. Cannot set false when source_hostname_key is set.

send_keepalive_packet

type
default
version
bool
false
1.14.0
Enables the TCP keepalive for sockets. See socket article for more details.

source_hostname_key

type
default
version
string
nil (no assign)
0.14.0
The field name of the client's hostname. If set, the client's hostname will be set to its key.

source_address_key

type
default
version
string
nil (no assign)
0.14.0
The field name of the client's address. If set, the client's address will be set to its key.

severity_key

type
default
version
string
nil (no assign)
1.7.3
The field name of the severity. If set, the severity will be set to its key.
If you set severity_key severity and got <6> started syslog message, severity field is info.

priority_key

type
default
version
string
nil (no assign)
0.14.10
This parameter is deprecated due to a misleading name. This sets severity, not priority.
This parameter will be removed in fluentd v2. Use severity_key instead.

facility_key

type
default
version
string
nil (no assign)
0.14.10
The field name of the facility. If set, the facility will be set to its key.
If you set facility_key facility and got <6> started syslog message, facility field is kern.

@log_level

The @log_level option allows the user to set different levels of logging for each plugin. The supported log levels are: fatal, error, warn, info, debug, and trace.
Please see the logging article for further details.

TCP Protocol and Message Delimiter

This plugin assumes for delimiter character between syslog messages in one TCP connection by default. If you use syslog library in your application with <transport tcp>, add to your syslog message. See also rfc6587.
If your syslog uses octet counting mode, set frame_type octet_count in in_syslog configuration. See also frame_type parameter.

Tips

How to Enable TLS Encryption

Since v1.5.0, in_syslog support TLS transport. Here is the configuration example with rsyslog:
  • in_syslog
<source>
@type syslog
port 5140
bind 0.0.0.0
<transport tls>
ca_path /etc/pki/ca.pem
cert_path /etc/pki/cert.pem
private_key_path /etc/pki/key.pem
private_key_passphrase PASSPHRASE
</transport>
tag system
</source>
  • rsyslog
$DefaultNetstreamDriverCAFile /etc/pki/ca.pem
$DefaultNetstreamDriver gtls
$ActionSendStreamDriverMode 1
$ActionSendStreamDriverAuthMode anon
*.* @@127.0.0.1:5140

Multi-process Environment

If you use this plugin under the multi-process environment, the port will be shared.
<system>
workers 3
</system>
​
<source>
@type syslog
port 5140
</source>
With this configuration, 3 workers share 5140 port. No need of an additional port. The incoming data will be routed to the three (3) workers automatically.

FAQ

Our system sends RFC3164/RFC5424 message but parse failure happens

First, check your message format follows RFC3164/RFC5424 or not. Some systems say RFC3164/RFC5424 but it sends non-RFC3164/RFC5424 message, e.g. invalid priority, different timestamp, lack/add fields.
If only timestamp is different, configure time_format in <parse> may help.
If other parts are different, the syslog parser cannot parse your message. To resolve the problem, there are several approaches:
  • Use regex parser or write your parser
  • Use in_udp/in_tcp with other parsers

Learn More

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.
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Last modified 1yr ago