syslog-ng Premium Edition 6.0.21 - Administration Guide

In order to use this destination, syslog-ng Premium Edition must run in server mode. Typically, only the central syslog-ng Premium Edition server uses this destination. For details on the server mode, see the section called “Server mode”.

This destination is only supported on the Linux platforms that use the linux glibc2.11 installer, including: Red Hat ES 7, Ubuntu 14.04 (Trusty Tahr).
Since syslog-ng PE uses the official Java Kafka producer, the kafka destination has significant memory usage.
The log messages of the underlying client libraries are available in the internal() source of syslog-ng PE.

Declaration:

@module mod-java
@include "scl.conf"

kafka(
    client_lib_dir(/opt/syslog-ng/lib/syslog-ng/java-modules/:<path-to-preinstalled-kafka-libraries>)
    kafka_bootstrap_servers("1.2.3.4:9092,192.168.0.2:9092")
    topic("${HOST}")

);

Example 7.13. Sending log data to Apache Kafka

The following example defines a kafka destination, using only the required parameters.

@module mod-java
@include "scl.conf"

destination d_kafka {
  kafka(
    client_lib_dir(/opt/syslog-ng/lib/syslog-ng/java-modules/KafkaDestination.jar:/usr/share/kafka/lib)
    kafka_bootstrap_servers("1.2.3.4:9092,192.168.0.2:9092")
    topic("${HOST}")
  );
};

To install the software required for the kafka destination, see Procedure 7.6, “Prerequisites”.
For details on how the kafka destination works, see the section called “How syslog-ng PE interacts with Apache Kafka”.
For the list of options, see the section called “Kafka destination options”.

Procedure 7.6. Prerequisites

To publish messages from syslog-ng PE to Apache Kafka, complete the following steps.

Steps:

If you want to use the Java-based modules of syslog-ng PE (for example, the Elasticsearch, HDFS, or Kafka destinations), download and install the Java Runtime Environment (JRE), 1.7 (or newer).

The Java-based modules of syslog-ng PE are tested and supported when using the Oracle implementation of Java. Other implementations are untested and unsupported, they may or may not work as expected.
Download the latest stable binary release of the Apache Kafka libraries (version 0.8.2 or newer) from http://kafka.apache.org/downloads.html.
Extract the Apache Kafka libraries into a single directory. If needed, collect the various .jar files into a single directory (for example, /opt/kafka/lib/) where syslog-ng PE can access them. You must specify this directory in the syslog-ng PE configuration file.
Check if the following files in the Kafka libraries have the same version number: slf4j-api-<version-number>.jar, slf4j-log4j12-<version-number>.jar. If the version number of these files is different, complete the following steps:
1. Delete one of the files (for example, slf4j-log4j12-<version-number>.jar).
2. Download a version that matches the version number of the other file (for example, 1.7.6) from the official SLF4J distribution.
3. Copy the downloaded file into the directory of your Kafka library files (for example, /opt/kafka/lib/).

How syslog-ng PE interacts with Apache Kafka

When stopping the syslog-ng PE application, syslog-ng PE will not stop until all Java threads are finished, including the threads started by the Kafka Producer. There is no way (except for the kill -9 command) to stop syslog-ng PE before the Kafka Producer stops. To change this behavior set the properties of the Kafka Producer in its properties file, and reference the file in the properties-file option.

The syslog-ng PE kafka destination tries to reconnect to the brokers in a tight loop. This can look as spinning, because of a lot of similar debug messages. To decrease the amount of such messages, set a bigger timeout using the following properties:

retry.backoff.ms=1000
reconnect.backoff.ms=1000

For details on using property files, see the section called “properties_file()”. For details on the properties that you can set in the property file, see the Apache Kafka documentation.

Kafka destination options

The kafka destination of syslog-ng PE can directly publish log messages to the Apache Kafka message bus, where subscribers can access them. The kafka destination has the following options.

Required options:

The following options are required: kafka-bootstrap-servers(), topic(). Note that to use kafka, you must add the following lines to the beginning of your syslog-ng PE configuration:

@module mod-java
@include "scl.conf"

client_lib_dir()

Type:	string
Default:	N/A

Description: Include the path to the directory where you copied the required libraries (see Procedure 7.6, “Prerequisites”), for example, client_lib_dir(/user/share/kafka/lib).

disk-buffer()

Description: This option enables putting outgoing messages into the disk buffer of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:

reliable()

Type: yes|no

Default: no

Description: If set to yes, syslog-ng PE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng PE crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no, the normal disk-buffer will be used. This provides a faster, but less reliable disk-buffer option.

Caution:

Hazard of data loss! If you change the value of reliable() option when there are messages in the disk-buffer, the messages stored in the disk-buffer will be lost.

dir()

Type: string

Default: N/A

Description: Defines the folder where the disk-buffer files are stored. This option has priority over --qdisk-dir=.

Caution:

When creating a new dir() option for a disk buffer, or modifying an existing one, make sure you delete the persist file, or at least remove the relevant persist-entry.

syslog-ng PE creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file or the relevant entry is not deleted after modifying the dir() option, then following a restart, syslog-ng PE will look for or create disk-buffer files in their old location. To ensure that syslog-ng PE uses the new dir() setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.

disk-buf-size()
Type:	number (bytes)
Default:
	Description: This is a required option. The maximum size of the disk-buffer in bytes. The minimum value is 1048576 bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old `log-disk-fifo-size()` option.

mem-buf-length()
Type:	number (messages)
Default:	10000
	Description: Use this option if the option `reliable()` is set to `no`. This option contains the number of messages stored in overflow queue. It replaces the old `log-fifo-size()` option. It inherits the value of the global `log-fifo-size()` option if provided. If it is not provided, the default value is `10000` messages. Note that this option will be ignored if the option `reliable()` is set to `yes`.

mem-buf-size()
Type:	number (bytes)
Default:	163840000
	Description: Use this option if the option `reliable()` is set to `yes`. This option contains the size of the messages in bytes that is used in the memory part of the disk buffer. It replaces the old `log-fifo-size()` option. It does not inherit the value of the global `log-fifo-size()` option, even if it is provided. Note that this option will be ignored if the option `reliable()` is set to `no`.

quot-size()
Type:	number (messages)
Default:	64
	Description: The number of messages stored in the output buffer of the destination.

Options reliable() and disk-buf-size() are required options.

Example 7.14. Examples for using disk-buffer()

In the following case reliable disk-buffer() is used.

destination d_demo {
    network(
            "127.0.0.1"
            port(3333)
            disk-buffer(
                mem-buf-size(10000)
                disk-buf-size(2000000)
                reliable(yes)
                dir("/tmp/disk-buffer")
            )
        );
};

In the following case normal disk-buffer() is used.

destination d_demo {
    network(
            "127.0.0.1"
            port(3333)
            disk-buffer(
                mem-buf-length(10000)
                disk-buf-size(2000000)
                reliable(no)
                dir("/tmp/disk-buffer")
            )
        );
};

kafka_bootstrap_servers()

Type:	list of hostnames
Default:

Description: Specifies the hostname or IP address of the Kafka server. When specifying an IP address, IPv4 (for example, 192.168.0.1) or IPv6 (for example, [::1]) can be used as well. Use a colon (:) after the address to specify the port number of the server. When specifying multiple addresses, use a comma to separate the addresses, for example, kafka-bootstrap-servers("127.0.0.1:2525,remote-server-hostname:6464")

frac-digits()

Type:	number (digits of fractions of a second)
Default:	Value of the global option (which defaults to 0)

Description: The syslog-ng application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received. Note that syslog-ng can add the fractions to non-ISO8601 timestamps as well.

on-error()

Accepted values:	drop-message\|drop-property\|fallback-to-string\|silently-drop-message\|silently-drop-property\|silently-fallback-to-string
Default:	Use the global setting (which defaults to `drop-message`)

Description: Controls what happens when type-casting fails and syslog-ng PE cannot convert some data to the specified type. By default, syslog-ng PE drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of syslog-ng PE.
drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.
fallback-to-string: Convert the property to string and log an error message to the internal() source.
silently-drop-message: Drop the entire message silently, without logging the error.
silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.
silently-fallback-to-string: Convert the property to string silently, without logging the error.

key()

Type:	template
Default:	N/A

Description: The key of the partition under which the message is published. You can use templates to change the topic dynamically based on the source or the content of the message, for example, key("${PROGRAM}").

log-fifo-size()

Type:	number (messages)
Default:	Use global setting.

Description: The number of messages that the output queue can store.

properties_file()

Type:	string (absolute path)
Default:	N/A

Description: The absolute path and filename of the Kafka properties file to load. For example, properties_file("/opt/syslog-ng/etc/kafka_dest.properties"). The syslog-ng PE application reads this file and passes the properties to the Kafka Producer. If a property is defined both in the syslog-ng PE configuration file (syslog-ng.conf) and in the properties file, then syslog-ng PE uses the definition from the syslog-ng PE configuration file.

The syslog-ng PE kafka destination supports all properties of the official Kafka producer. For details, see the Apache Kafka documentation.

The kafka-bootstrap-servers option is translated to the bootstrap.servers property.

For example, the following properties file defines the acknowledgement method and compression:

acks=all
compression.type=snappy

retries()

Type:	number (of attempts)
Default:	3

Description: The number of times syslog-ng PE attempts to send a message to this destination. If syslog-ng PE could not send a message, it will try again until the number of attempts reaches retries, then drops the message.

template()

Type:	template or template function
Default:	$ISODATE $HOST $MSGHDR$MSG\n

Description: The message as published to Apache Kafka. You can use templates and template functions (for example, format-json()) to format the message, for example, template("$(format-json --scope rfc5424 --exclude DATE --key ISODATE)").

For details on formatting messages in JSON format, see the section called “format-json”.

throttle()

Type:	number (messages per second)
Default:	0

Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using disk-buffer as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

topic()

Type:	template
Default:	N/A

Description: The Kafka topic under which the message is published. You can use templates to change the topic dynamically based on the source or the content of the message, for example, topic("${HOST}").

sync_send()

Type:	true \| false
Default:	false

Description: When sync_send is set to true, syslog-ng PE sends the message reliably: it sends a message to the Kafka server, then waits for a reply. In case of failure, syslog-ng PE repeats sending the message, as set in the retries() parameter. If sending the message fails for retries() times, syslog-ng PE drops the message.

This method ensures reliable message transfer, but is very slow.

When sync_send is set to false, syslog-ng PE sends messages asynchronously, and receives the response asynchronously. In case of a problem, syslog-ng PE cannot resend the messages.

This method is fast, but the transfer is not reliable. Several thousands of messages can be lost before syslog-ng PE recognizes the error.

time-zone()

Type:	name of the timezone, or the timezone offset
Default:	unspecified

Description: Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, HOUR. For the complete list of such macros, see the section called “Date-related macros”.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

ts-format()

Type:	rfc3164, bsd, rfc3339, iso
Default:	Use the global option (which defaults to rfc3164)

Description: Override the global timestamp format (set in the global ts-format() parameter) for the specific destination. For details, see the section called “A note on timezones and timestamps”.

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