syslog-ng Open Source Edition 3.16 - Administration Guide

Version 3.8 of syslog-ng OSE can directly post log messages to web services using the HTTP protocol, without having to use Java. The current implementation has the following limitations:

Only the PUT and the POST methods are supported.

HTTPS connection, as well as password- and certificate-based authentication is supported.

Example: Client certificate authentication with HTTPS

destination d_https { 
  http(
    [...]
    ca-file("/<path-to-certificate-directory>/ca-crt.pem")
    ca-dir("/<path-to-certificate-directory>/")
    cert-file("/<path-to-certificate-directory>/server-crt.pem")
    key-file("/<path-to-certificate-directory>/server-key.pem")
    [...]
  ); 
};

Declaration:

destination d_http {
    http(
        url("<web-service-IP-or-hostname>")
        method("<HTTP-method>")
        user-agent("<USER-AGENT-message-value>")
        user("<username>")
        password("<password>")
    );
};

Example: Sending log data to a web service

The following example defines an http destination.

destination d_http {
  http(
    url("http://127.0.0.1:8000")
    method("PUT")
    user-agent("syslog-ng User Agent")
    user("user")
    password("password")
    headers("HEADER1: header1", "HEADER2: header2")
    body("${ISODATE} ${MESSAGE}")
  );
};

log
    { source(s_file); destination(d_http); flags(flow-control); };

You can also use the http() destination to forward log messages to Splunk using syslog-ng OSE.

HTTP destination options

destination: Forward, send, and store log messages > http: Posting messages over HTTP without Java > HTTP destination options

The http destination of syslog-ng OSE can directly post log messages to web services using the HTTP protocol. The http destination has the following options.

body()

Type:	string or template
Default:

Description: The body of the HTTP request, for example, body("${ISODATE} ${MESSAGE}"). You can use strings, macros, and template functions in the body. If not set, it will contain the message received from the source by default.

ca-dir()

Accepted values:	Directory name
Default:	none

Description: Name of a directory, that contains a set of trusted CA certificates in PEM format. The CA certificate files have to be named after the 32-bit hash of the subject's name. This naming can be created using the c_rehash utility in openssl. For an example, see Configuring TLS on the syslog-ng clients. The syslog-ng OSE application uses the CA certificates in this directory to validate the certificate of the peer.

An alternative way to specify this option is to put into a tls() block and specify it there, together with any other TLS options. This allows you to separate these options and ensure better readability.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

Make sure that you specify TLS options either using their own dedicated option (ca-dir(), ca-file(), cert-file(), cipher-suite(), key-file(), peer-verify(), and ssl-version()), or using the tls() block and inserting the relevant options within tls(). Avoid mixing the two methods. In case you do specify TLS options in both ways, the one that comes later in the configuration file will take effect.

ca-file()

Accepted values:	Filename
Default:	none

Description: Name of a file that contains an X.509 CA certificate (or a certificate chain) in PEM format. The syslog-ng OSE application uses this certificate to validate the certificate of the HTTPS server. If the file contains a certificate chain, the file must begin with the certificate of the host, followed by the CA certificate that signed the certificate of the host, and any other signing CAs in order.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

cert-file()

Accepted values:	Filename
Default:	none

Description: Name of a file, that contains an X.509 certificate (or a certificate chain) in PEM format, suitable as a TLS certificate, matching the private key set in the key-file() option. The syslog-ng OSE application uses this certificate to authenticate the syslog-ng OSE client on the destination server. If the file contains a certificate chain, the file must begin with the certificate of the host, followed by the CA certificate that signed the certificate of the host, and any other signing CAs in order.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

cipher-suite()

Accepted values:	Name of a cipher, or a colon-separated list
Default:	Depends on the OpenSSL version that syslog-ng OSE uses

Description: Specifies the cipher, hash, and key-exchange algorithms used for the encryption, for example, ECDHE-ECDSA-AES256-SHA384. The list of available algorithms depends on the version of OpenSSL used to compile syslog-ng OSE. To specify multiple ciphers, separate the cipher names with a colon, and enclose the list between double-quotes, for example:

cipher-suite("ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384")

For a list of available algorithms, execute the openssl ciphers -v command. The first column of the output contains the name of the algorithms to use in the cipher-suite() option, the second column specifies which encryption protocol uses the algorithm (for example, TLSv1.2). That way, the cipher-suite() also determines the encryption protocol used in the connection: to disable SSLv3, use an algorithm that is available only in TLSv1.2, and that both the client and the server supports. You can also specify the encryption protocols using ssl-options().

You can also use the following command to automatically list only ciphers permitted in a specific encryption protocol, for example, TLSv1.2:

echo "cipher-suite(\"$(openssl ciphers -v | grep TLSv1.2 | awk '{print $1}' | xargs echo -n | sed 's/ /:/g' | sed -e 's/:$//')\")"

Note that starting with version 3.10, when syslog-ng OSE receives TLS-encrypted connections, the order of ciphers set on the syslog-ng OSE server takes precedence over the client settings.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

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:

Description: If set to yes, syslog-ng OSE cannot lose logs in case of reload/restart, unreachable destination or syslog-ng OSE 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.

Caution:

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

syslog-ng OSE creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir() option, then following a restart, syslog-ng OSE will look for or create disk-buffer files in their old location. To ensure that syslog-ng OSE 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.

qout-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: 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")
        )
    );
};

headers()

Type:	string list
Default:

Description: Custom HTTP headers to include in the request, for example, headers("HEADER1: header1", "HEADER2: header2"). If not set, only the default headers are included, but no custom headers.

The following headers are included by default:

X-Syslog-Host: <host>
X-Syslog-Program: <program>
X-Syslog-Facility: <facility>
X-Syslog-Level: <loglevel/priority>

hook-commands()

Description: This option makes it possible to execute external programs when the relevant driver is initialized or torn down. The hook-commands() can be used with all source and destination drivers with the exception of the usertty() and internal() drivers.

NOTE: The syslog-ng OSE application must be able to start and restart the external program, and have the necessary permissions to do so. For example, if your host is running AppArmor or SELinux, you might have to modify your AppArmor or SELinux configuration to enable syslog-ng OSE to execute external applications.

Using the hook-commands() when syslog-ng OSE starts or stops

To execute an external program when syslog-ng OSE starts or stops, use the following options:

startup()
Type:	string
Default:	N/A
Description: Defines the external program that is executed as syslog-ng OSE starts.

shutdown()
Type:	string
Default:	N/A
Description: Defines the external program that is executed as syslog-ng OSE stops.

Using the hook-commands() when syslog-ng OSE reloads

To execute an external program when the syslog-ng OSE configuration is initiated or torn down, for example, on startup/shutdown or during a syslog-ng OSE reload, use the following options:

setup()
Type:	string
Default:	N/A
Description: Defines an external program that is executed when the syslog-ng OSE configuration is initiated, for example, on startup or during a syslog-ng OSE reload.

teardown()
Type:	string
Default:	N/A
Description: Defines an external program that is executed when the syslog-ng OSE configuration is stopped or torn down, for example, on shutdown or during a syslog-ng OSE reload.

Example: Using the hook-commands() with a network source

In the following example, the hook-commands() is used with the network() driver and it opens an iptables port automatically as syslog-ng OSE is started/stopped.

The assumption in this example is that the LOGCHAIN chain is part of a larger ruleset that routes traffic to it. Whenever the syslog-ng OSE created rule is there, packets can flow, otherwise the port is closed.

source {
   network(transport(udp)
	hook-commands(
          startup("iptables -I LOGCHAIN 1 -p udp --dport 514 -j ACCEPT")
          shutdown("iptables -D LOGCHAIN 1")
        )
     );
};

log-fifo-size()

Type:	number
Default:	Use global setting.

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

key-file()

Accepted values:	Filename
Default:	none

Description: The name of a file that contains an unencrypted private key in PEM format, suitable as a TLS key. If properly configured, the syslog-ng OSE application uses this private key and the matching certificate (set in the cert-file() option) to authenticate the syslog-ng OSE client on the destination server.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

method()

Type:	POST \| PUT
Default:	POST

Description: Specifies the HTTP method to use when sending the message to the server.

password()

Type:	string
Default:

Description: The password that syslog-ng OSE uses to authenticate on the server where it sends the messages.

peer-verify()

Accepted values:	yes \| no
Default:	yes

Description: Verification method of the peer. The following table summarizes the possible options and their results depending on the certificate of the peer.

		The remote peer has:
		no certificate	invalid certificate	valid certificate
Local peer-verify() setting	no (optional-untrusted)	TLS-encryption	TLS-encryption	TLS-encryption
Local peer-verify() setting	yes (required-trusted)	rejected connection	rejected connection	TLS-encryption

For untrusted certificates only the existence of the certificate is checked, but it does not have to be valid — syslog-ng accepts the certificate even if it is expired, signed by an unknown CA, or its CN and the name of the machine mismatches.

Caution:

When validating a certificate, the entire certificate chain must be valid, including the CA certificate. If any certificate of the chain is invalid, syslog-ng OSE will reject the connection.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

persist-name()

Type:	string
Default:

Description:If you receive the following error message during syslog-ng OSE startup, set the persist-name() option of the duplicate drivers:

Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down.

This error happens if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the persist-name() of the drivers to a custom string, for example, persist-name("example-persist-name1").

retries()

Type:	number (of attempts)
Default:	3

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

To handle HTTP error responses, if the HTTP server returns 5xx codes, syslog-ng OSE will attempt to resend messages until the number of attempts reaches retries. If the HTTP server returns 4xx codes, syslog-ng OSE will drop the messages.

ssl-version()

Type:	string
Default:	None, uses the libcurl default

Description: Specifies the permitted SSL/TLS version. Possible values: sslv2, sslv3, tlsv1, tlsv1_0, tlsv1_1, tlsv1_2.

Declaration:

destination  d_http {
	http(
		url("http://127.0.0.1:8080")
		tls(
			ca-dir("dir")
			ca-file("ca")
			cert-file("cert")
			cipher-suite("cipher") 
			key-file("key")
			peer-verify(yes|no)
			ssl-version(<the permitted SSL/TLS version>)
		)
	);
};

template()

Type:	string
Default:	A format conforming to the default logfile format.

Description: Specifies a template defining the logformat to be used in the destination. Macros are described in Macros of syslog-ng OSE. Please note that for network destinations it might not be appropriate to change the template as it changes the on-wire format of the syslog protocol which might not be tolerated by stock syslog receivers (like syslogd or syslog-ng itself). For network destinations make sure the receiver can cope with the custom format defined.

throttle()

Type:	number
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.

timeout()

Type:	number [seconds]
Default:	0

Description: The value (in seconds) to wait for an operation to complete, and attempt to reconnect the server if exceeded. By default, the timeout value is 0, meaning that there is no timeout. Available in version 3.11 and later.

url()

Type:	URL
Default:	http://localhost/

Description: Specifies the hostname or IP address and optionally the port number of the web service that can receive log data via HTTP. Use a colon (:) after the address to specify the port number of the server. For example: http://127.0.0.1:8000

user-agent()

Type:	string
Default:	syslog-ng [version]/libcurl[version]

Description: The value of the USER-AGENT header in the messages sent to the server.

user()

Type:	string
Default:

Description: The username that syslog-ng OSE uses to authenticate on the server where it sends the messages.

kafka: Publishing messages to Apache Kafka

destination: Forward, send, and store log messages > kafka: Publishing messages to Apache Kafka

Starting with version 3.7, syslog-ng OSE can directly publish log messages to the Apache Kafka message bus, where subscribers can access them.

This destination is only supported on the Linux platform.
Since syslog-ng OSE 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 OSE.

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: 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 Prerequisites.
For details on how the kafka destination works, see How syslog-ng OSE interacts with Apache Kafka.
For the list of options, see Kafka destination options.

The kafka() driver is actually a reusable configuration snippet configured to receive log messages using the Java language-binding of syslog-ng OSE. For details on using or writing such configuration snippets, see Reusing configuration blocks. You can find the source of the kafka configuration snippet on GitHub. For details on extending syslog-ng OSE in Java, see the Getting started with syslog-ng development guide.

Prerequisites

destination: Forward, send, and store log messages > kafka: Publishing messages to Apache Kafka > Prerequisites

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

Steps:

If you want to use the Java-based modules of syslog-ng OSE (for example, the Elasticsearch, HDFS, or Kafka destinations), you must compile syslog-ng OSE with Java support.
- Download and install the Java Runtime Environment (JRE), 1.7 (or newer). You can use OpenJDK or Oracle JDK, other implementations are not tested.
- Install gradle version 2.2.1 or newer.
- Set LD_LIBRARY_PATH to include the libjvm.so file, for example:LD_LIBRARY_PATH=/usr/lib/jvm/java-7-openjdk-amd64/jre/lib/amd64/server:$LD_LIBRARY_PATH
  
  Note that many platforms have a simplified links for Java libraries. Use the simplified path if available. If you use a startup script to start syslog-ng OSE set LD_LIBRARY_PATH in the script as well.
- If you are behind an HTTP proxy, create a gradle.properties under the modules/java-modules/ directory. Set the proxy parameters in the file. For details, see The Gradle User Guide.
Download the latest stable binary release of the Apache Kafka libraries (version 0.9 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 OSE can access them. You must specify this directory in the syslog-ng OSE 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/).

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syslog-ng Open Source Edition 3.16 - Administration Guide

http: Posting messages over HTTP without Java

Example: Client certificate authentication with HTTPS

Declaration:

Example: Sending log data to a web service

HTTP destination options

body()

ca-dir()

Declaration:

ca-file()

Declaration:

cert-file()

Declaration:

cipher-suite()

Declaration:

disk-buffer()

Example: Examples for using disk-buffer()

headers()

hook-commands()

Using the hook-commands() when syslog-ng OSE starts or stops

Using the hook-commands() when syslog-ng OSE reloads

Example: Using the hook-commands() with a network source

log-fifo-size()

key-file()

Declaration:

method()

password()

peer-verify()

Declaration:

persist-name()

retries()

ssl-version()

Declaration:

template()

throttle()

timeout()

url()

user-agent()

user()

kafka: Publishing messages to Apache Kafka

Declaration:

Example: Sending log data to Apache Kafka

Prerequisites

Steps: