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syslog-ng Open Source Edition 3.26 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng OSE quick-start guide The syslog-ng OSE configuration file source: Read, receive, and collect log messages
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs network: Collecting messages using the RFC3164 protocol (network() driver) nodejs: Receiving JSON messages from nodejs applications mbox: Converting local email messages to log messages osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes pacct: Collecting process accounting logs on Linux program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps sun-streams: Collecting messages on Sun Solaris syslog: Collecting messages using the IETF syslog protocol (syslog() driver) system: Collecting the system-specific log messages of a platform systemd-journal: Collecting messages from the systemd-journal system log storage systemd-syslog: Collecting systemd messages using a socket tcp, tcp6, udp, udp6: Collecting messages from remote hosts using the BSD syslog protocol— OBSOLETE unix-stream, unix-dgram: Collecting messages from UNIX domain sockets stdin: Collecting messages from the standard input stream
destination: Forward, send, and store log messages
amqp: Publishing messages using AMQP collectd: sending metrics to collectd elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Bulk API file: Storing messages in plain-text files graphite: Sending metrics to Graphite Sending logs to Graylog hdfs: Storing messages on the Hadoop Distributed File System (HDFS) Posting messages over HTTP http: Posting messages over HTTP without Java kafka: Publishing messages to Apache Kafka (Java implementation) kafka: Publishing messages to Apache Kafka (C implementation, using the librdkafka client) loggly: Using Loggly logmatic: Using Logmatic.io mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) osquery: Sending log messages to osquery's syslog table pipe: Sending messages to named pipes program: Sending messages to external applications pseudofile() python: writing custom Python destinations redis: Storing name-value pairs in Redis riemann: Monitoring your data with Riemann slack: Sending alerts and notifications to a Slack channel smtp: Generating SMTP messages (email) from logs snmp: Sending SNMP traps Splunk: Sending log messages to Splunk sql: Storing messages in an SQL database stomp: Publishing messages using STOMP syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng(): Forward logs to another syslog-ng node tcp, tcp6, udp, udp6: Sending messages to a remote log server using the legacy BSD-syslog protocol (tcp(), udp() drivers) Telegram: Sending messages to Telegram unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal: usertty() destination Write your own custom destination in Java or Python Client-side failover
log: Filter and route log messages using log paths, flags, and filters Global options of syslog-ng OSE TLS-encrypted message transfer template and rewrite: Format, modify, and manipulate log messages parser: Parse and segment structured messages db-parser: Process message content with a pattern database (patterndb) Correlating log messages Enriching log messages with external data Statistics of syslog-ng Multithreading and scaling in syslog-ng OSE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Creative Commons Attribution Non-commercial No Derivatives (by-nc-nd) License Glossary

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.

batch-bytes()
Accepted values: number [bytes]
Default: none

Description: Sets the maximum size of payload in a batch. If the size of the messages reaches this value, syslog-ng OSE sends the batch to the destination even if the number of messages is less than the value of the batch-lines() option.

Note that if the batch-timeout() option is enabled and the queue becomes empty, syslog-ng OSE flushes the messages only if batch-timeout() expires, or the batch reaches the limit set in batch-bytes().

Available in syslog-ng OSE version 3.19 and later.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

batch-lines()
Type: number
Default: 1

Description: Specifies how many lines are flushed to a destination in one batch. The syslog-ng OSE application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency.

For example, if you set batch-lines() to 100, syslog-ng OSE waits for 100 messages.

If the batch-timeout() option is disabled, the syslog-ng OSE application flushes the messages if it has sent batch-lines() number of messages, or the queue became empty. If you stop or reload syslog-ng OSE or in case of network sources, the connection with the client is closed, syslog-ng OSE automatically sends the unsent messages to the destination.

Note that if the batch-timeout() option is enabled and the queue becomes empty, syslog-ng OSE flushes the messages only if batch-timeout() expires, or the batch reaches the limit set in batch-lines().

For optimal performance, make sure that the syslog-ng OSE source that feeds messages to this destination is configured properly: the value of the log-iw-size() option of the source must be higher than the batch-lines()*workers() of the destination. Otherwise, the size of the batches cannot reach the batch-lines() limit.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

batch-timeout()
Type: time in milliseconds
Default: -1 (disabled)

Description: Specifies the time syslog-ng OSE waits for lines to accumulate in the output buffer. The syslog-ng OSE application sends batches to the destinations evenly. The timer starts when the first message arrives to the buffer, so if only few messages arrive, syslog-ng OSE sends messages to the destination at most once every batch-timeout() milliseconds.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

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.

body-prefix()
Accepted values: string
Default: none

Description: The string syslog-ng OSE puts at the beginning of the body of the HTTP request, before the log message. Available in syslog-ng OSE version 3.18 and later.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

body-suffix()
Accepted values: string
Default: none

Description: The string syslog-ng OSE puts to the end of the body of the HTTP request, after the log message. Available in syslog-ng OSE version 3.18 and later.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

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 it into a tls() block, together with any other TLS options. This allows you to separate these options and ensure better readability.

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.

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>)
		)
	);
};
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.

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

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.

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.

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

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.

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.

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

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.

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>)
		)
	);
};
delimiter()
Accepted values: string
Default: newline character

Description: By default, syslog-ng OSE separates the log messages of the batch with a newline character. You can specify a different delimiter by using the delimiter() option. Available in syslog-ng OSE version 3.18 and later.

For details on how this option influences HTTP batch mode, see http: Posting messages over HTTP without Java

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 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.

compaction()
Type: yes|no
Default: no

Description: If set to yes, syslog-ng OSE prunes the unused space in the LogMessage representation, making the disk queue size smaller at the cost of some CPU time. Setting the compaction() argument to yes is recommended when numerous name-value pairs are unset during processing, or when the same names are set multiple times.

NOTE: Simply unsetting these name-value pairs by using the unset() rewrite operation is not enough, as due to performance reasons that help when syslog-ng is CPU bound, the internal representation of a LogMessage will not release the memory associated with these name-value pairs. In some cases, however, the size of this overhead becomes significant (the raw message size can grow up to four times its original size), which unnecessarily increases the disk queue file size. For these cases, the compaction will drop "unset" values, making the LogMessage representation smaller at the cost of some CPU time required to perform compaction.

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. Note that if you change the value of this option and the disk-buffer already exists, the change will take effect when the disk-buffer becomes empty.

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.

The http() destination supports only unencrypted key files (that is, the private key cannot be password-protected).

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

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.

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
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.

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

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.

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").

response-action()
Type: list
Default: N/A (see below)

Description: Specifies what syslog-ng OSE does with the log message, based on the response code received from the HTTP server. If the server returns a status code beginning with 2 (for example, 200), syslog-ng OSE assumes the message was successfully sent. Otherwise, the action listed in the following table is applied. For status codes not listed in the following table, if the status code begins with 2 (for example, 299), syslog-ng OSE assumes the message was successfully sent. For other status codes, syslog-ng OSE disconnects. The following actions are possible:

  • disconnect: Keep trying to resend the message indefinitely.

  • drop: Drop the message without trying to resend it.

  • retry: Retry sending the message for a maximum of retries() times (3 by default).

  • success: Assume the message was successfully sent.

|------+-----------------------------------+------------|
| code | explanation                       | action     |
|------+-----------------------------------+------------|
|  100 | "Continue"                        | disconnect |
|  101 | "Switching Protocols"             | disconnect |
|  102 | "Processing"                      | retry      |
|  103 | "Early Hints"                     | retry      |
|  200 | "OK"                              | success    |
|  201 | "Created"                         | success    |
|  202 | "Accepted"                        | success    |
|  203 | "Non-Authoritative Information"   | success    |
|  204 | "No Content"                      | success    |
|  205 | "Reset Content"                   | success    |
|  206 | "Partial Content"                 | success    |
|  300 | "Multiple Choices"                | disconnect |
|  301 | "Moved Permanently"               | disconnect |
|  302 | "Found"                           | disconnect |
|  303 | "See Other"                       | disconnect |
|  304 | "Not Modified"                    | retry      |
|  307 | "Temporary Redirect"              | disconnect |
|  308 | "Permanent Redirect"              | disconnect |
|  400 | "Bad Request"                     | disconnect |
|  401 | "Unauthorized"                    | disconnect |
|  402 | "Payment Required"                | disconnect |
|  403 | "Forbidden"                       | disconnect |
|  404 | "Not Found"                       | disconnect |
|  405 | "Method Not Allowed"              | disconnect |
|  406 | "Not Acceptable"                  | disconnect |
|  407 | "Proxy Authentication Required"   | disconnect |
|  408 | "Request Timeout"                 | disconnect |
|  409 | "Conflict"                        | disconnect |
|  410 | "Gone"                            | drop       |
|  411 | "Length Required"                 | disconnect |
|  412 | "Precondition Failed"             | disconnect |
|  413 | "Payload Too Large"               | disconnect |
|  414 | "URI Too Long"                    | disconnect |
|  415 | "Unsupported Media Type"          | disconnect |
|  416 | "Range Not Satisfiable"           | drop       |
|  417 | "Expectation Failed"              | disconnect |
|  418 | "I'm a teapot"                    | disconnect |
|  421 | "Misdirected Request"             | disconnect |
|  422 | "Unprocessable Entity"            | drop       |
|  423 | "Locked"                          | disconnect |
|  424 | "Failed Dependency"               | drop       |
|  425 | "Too Early"                       | drop       |
|  426 | "Upgrade Required"                | disconnect |
|  428 | "Precondition Required"           | retry      |
|  429 | "Too Many Requests"               | disconnect |
|  431 | "Request Header Fields Too Large" | disconnect |
|  451 | "Unavailable For Legal Reasons"   | drop       |
|  500 | "Internal Server Error"           | disconnect |
|  501 | "Not Implemented"                 | disconnect |
|  502 | "Bad Gateway"                     | disconnect |
|  503 | "Service Unavailable"             | disconnect |
|  504 | "Gateway Timeout"                 | retry      |
|  505 | "HTTP Version Not Supported"      | disconnect |
|  506 | "Variant Also Negotiates"         | disconnect |
|  507 | "Insufficient Storage"            | disconnect |
|  508 | "Loop Detected"                   | drop       |
|  510 | "Not Extended"                    | disconnect |
|  511 | "Network Authentication Required" | disconnect |
|------+-----------------------------------+------------|

To customize the action to take for a particular response code, use the following format: response-action(<response-code> => <action>. To customize multiple response code-action pairs, separate them with a comma, for example:

 http(
    url("http://localhost:8080")
    response-action(418 => drop, 404 => retry)
);
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, tlsv1_3.

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

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.

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 or list of URLs
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

In case the server on the specified URL returns a redirect request, syslog-ng OSE automatically follows maximum 3 redirects. Only HTTP and HTTPS based redirections are supported.

Starting with version 3.19, you can specify multiple URLs, for example, url("site1", "site2"). In this case, syslog-ng OSE sends log messages to the specified URLs in a load-balance fashion. This means that syslog-ng OSE sends each message to only one URL. For example, you can use this to send the messages to a set of ingestion nodes or indexers of your SIEM solution if a single node cannot handle the load. Note that the order of the messages as they arrive on the servers can differ from the order syslog-ng OSE has received them, so use load-balancing only if your server can use the timestamp from the messages. If the server uses the timestamp when it receives the messages, the order of the messages will be incorrect.

Caution:

If you set multiple URLs in the url() option, set the persist-name() option as well to avoid data loss.

Starting with version syslog-ng OSE version 3.22, you can use any of the following formats to specify multiple URLs:

url("server1", "server2", "server3"); # comma-separated strings
url("server1" "server2" "server3"); # space-separated strings
url("server1 server2 server3"); # space-separated within a single string
url("server1,server2,server3"); # comma-separated within a single string
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.

use-system-cert-store()
Type: yes | no
Default: no

Description: Use the certificate store of the system for verifying HTTPS certificates. For details, see the curl documentation.

workers()
Type: integer
Default: 1

Description: Specifies the number of worker threads (at least 1) that syslog-ng OSE uses to send messages to the server. Increasing the number of worker threads can drastically improve the performance of the destination.

Caution:

Hazard of data loss. When you use more than one worker threads together with disk-based buffering, syslog-ng OSE creates a separate disk buffer for each worker thread. This means that decreasing the number of workers can result in losing data currently stored in the disk buffer files. Do not decrease the number of workers when the disk buffer files are in use.

If you are using load-balancing (that is, you have configured multiple servers in the url() option), increase the number of worker threads at least to the number of servers. For example, if you have set three URLs (url("site1", "site2", "site3")), set the workers() option to 3 or more.


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The Azure auth header plugin

This section describes the syslog-ng Open Source Edition (syslog-ng OSE) application's Azure auth header plugin.

For more information about modules in syslog-ng OSE, see Modules in syslog-ng Open Source Edition (syslog-ng OSE).

The Azure auth header plugin is a signal-slot mechanism-based syslog-ng OSE module that generates authorization headers for applications that connect to Microsoft Azure.

Defining the Azure auth header plugin

You can define the Azure auth header plugin by the following:

azure-auth-header(
  method("POST")
  path("/api/logs")
  content-type("application/json")
  workspace-id("<workspace-id>")
  secret("<auth-secret>")
)
Options

NOTE: All these options are mandatory. They are used as input for the method that calculates the authorization header.


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The Python HTTP header plugin

This section describes the syslog-ng Open Source Edition (syslog-ng OSE) application's Python HTTP header plugin.

For more information about modules in syslog-ng OSE, see Modules in syslog-ng Open Source Edition (syslog-ng OSE).

The syslog-ng OSE application supports adding custom headers to HTTP requests using the Python programming language.

Prerequisites

NOTE: Before you use the python-http-header plugin, make sure that your syslog-ng OSE appliance was compiled with Python support. If you installed syslog-ng OSE from a package, make sure that the subpackage containing Python support is also installed.

Configuration
destination d_http {
  http(
    python_http_header(
      class("<class-name>")
      options("options-key1", "option-value1")
      options("options-key2", "option-value2")
      mark-errors-as-critical(no))
    url("http://127.0.0.1:8888")
  );
};

Options used in the configuration

  • class: Mandatory option. It refers to the user's Python class that implements the python-http-header interface. It can be mymodule.MyClass if the class MyClass is put into a mymodule.py module, or simply MyClass if the user's code is provided inline in the configuration, using the python { ... }; keyword.

    NOTE: If you put the class implementation into its own module, it should be put into a standard location, or made available with the PYTHONPATH environment variable.

  • options("key" "value"): Optional option. Multiple options can be specified at the same time. The syslog-ng OSE application will build a Python dictionary, which will be available in the __init__ method.
  • mark-errors-as-critical(yes|no): Optional option. Its default value is yes. In case there is a Python error, this parameter decides if the HTTP destination will still try to send the request with the failed headers, or disconnect instead.
Defining the python-http-header() interface

You can define the Python interface with the following:

class TestCounter():
  def __init__(self, options):
    self.key = options["value"]

  def get_headers(self, body, headers):
    return ["header1: value1", "header2: value2"]

  def on_http_response_received(self, http_code):
    print("HTTP response code received: {}".format(http_code))

By default, when the signal_http_header_request is emitted by the HTTP module, the connected slot automatically executes the Python code.

NOTE: If the plugin fails, the HTTP module does not send the HTTP request without the header items by default. If you want the HTTP module to try sending the request without the header items, disable the mark-errors-as-critical function.

Methods used in the configuration

  • __init__(self, options): Optional method. The options specified in the syslog-ng OSE configuration can be stored in the instance using this method.
  • get_headers(self, body, headers): Mandatory method. Returns a list of strings of form ["header: value", ...]. The returned headers will be set for the outgoing HTTP request. The body contains the body of the HTTP request. The headers contain the current headers that the HTTP destination has already added to the request.
  • on_http_response_received(self, http_code): Optional method. If specified, syslog-ng OSE inserts the http_code of the previous response. This can be used to handle error (for example, for recreating auth headers, or dropping cache).
Example configuration for using the Python HTTP header plugin

The following example can be copy-pasted and used as a template for using the Python HTTP header plugin in your configuration.

python {
from syslogng import Logger
					
logger = Logger()
					
class TestCounter():
    def __init__(self, options):
        self.header = options["header"]
        self.counter = int(options["counter"])
        logger.debug(f"TestCounter class instantiated; options={options}")
					
    def get_headers(self, body, headers):
        logger.debug(f"get_headers() called, received body={body}, headers={headers}")
					
        response = ["{}: {}".format(self.header, self.counter)]
        self.counter += 1
        return response
					
    def on_http_response_received(self, http_code):
        self.counter += http_code
        logger.debug("HTTP response code received: {}".format(http_code))
					
    def __del__(self):
        logger.debug("Deleting TestCounter class instance")
};
					
source s_network {
  network(port(5555));
};
					
destination d_http {
    http(
        python_http_header(
            class("TestCounter")
            options("header", "X-Test-Python-Counter")
            options("counter", 11)
            # this means that syslog-ng will keep trying to send the http request even when this module fails
            mark-errors-as-critical(no)
        )
        url("http://127.0.0.1:8888")
    );
};
					
log {
    source(s_network);
    destination(d_http);
    flags(flow-control);
};

Caution:

Although it is possible to configure multiple HTTP workers for syslog-ng OSE, the syslog-ng OSE application can only embed a single Python interpreter at the same time. As a result, if you configure more than one HTTP workers on your syslog-ng OSE application, the Python code will run in concurrent mode. To protect the state of the object, you may need to use locks.

For more information about using locks, see Introduction to the Python HTTP header.


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kafka: Publishing messages to Apache Kafka (Java implementation)

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:
@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.

@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}")
  );
};

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.

NOTE:

If you delete all Java destinations from your configuration and reload syslog-ng, the JVM is not used anymore, but it is still running. If you want to stop JVM, stop syslog-ng and then start syslog-ng again.


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