Slack destination options

This section describes the options of the slack() destination in syslog-ng OSE.

The slack destination of syslog-ng OSE can directly post log messages and notifications to Slack channels. The slack destination has the following options.

author-name()

Type:	string or template
Default:	'host: ${HOST} \| program: ${PROGRAM}(${PID}) \| severity: ${PRIORITY}'

Description: The sender of the message as displayed in Slack. For details, see the author_name option in the Slack documentation.

author-link()

Type:	string or URL
Default:	None

Description: A hyperlink for the sender of the message as displayed in Slack. For details, see the author_link option in the Slack documentation.

author-icon()

Type:	URL
Default:	None

Description: A hyperlink for icon of the author to be displayed in Slack. For details, see the author_icon option in the Slack documentation.

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.

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.

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.

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.

ca-dir()

Type:	Directory name
Default:	none

Description: The 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 OSE clients. The syslog-ng OSE application uses the CA certificates in this directory to validate the certificate of the peer.

This option can be used together with the optional ca-file() option.

NOTE: During a TLS handshake, syslog-ng OSE automatically sets the certificate_authorities field of the certificate request based on the ca-file() and ca-dir() options.

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.

Make sure that you specify TLS options either using their own dedicated option (ca-file(), cert-file(), key-file(), and peer-verify()), 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()

Type:	File name
Default:	empty

Description: Optional. The name of a file that contains a set of trusted CA certificates in PEM format. The syslog-ng OSE application uses the CA certificates in this file to validate the certificate of the peer.

Example format in configuration:

ca-file("/etc/pki/tls/certs/ca-bundle.crt")

NOTE: The ca-file() option can be used together with the ca-dir() option, and it is relevant when peer-verify() is set to other than no or optional-untrusted.

NOTE: During a TLS handshake, syslog-ng OSE automatically sets the certificate_authorities field of the certificate request based on the ca-file() and ca-dir() options.

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")
                cert-file("cert")
                cipher-suite("cipher")
                key-file("key")
                peer-verify(yes|no)
                ssl-version(<the permitted SSL/TLS version>)
        )
    );
};

colors()

Type:	list of colors in hexadecimal format
Default:	'#512E5F,#B03A2E,#E74C3C,#F39C12,#F8C471,#7DCEA0,#5DADE2,#85929E'

Description: The colors to be assigned to the messages of different importance levels.

color-chooser()

Type:	integer or template
Default:	'${LEVEL_NUM}'

Description: An integer that assigns a color to the message from the list of colors set in the colors() option.

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 suboptions:

capacity-bytes()

Type:	number (bytes)
Default:	1 MiB

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.

In syslog-ng OSE version 4.2 and earlier, this option was called disk-buf-size().

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 OSE 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.

flow-control-window-bytes()

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.

In syslog-ng OSE version 4.2 and earlier, this option was called mem-buf-size().

flow-control-window-size()

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.

In syslog-ng OSE version 4.2 and earlier, this option was called mem-buf-length().

front-cache-size()

Type:	number(messages)
Default:	1000

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 capacity-bytes() are required options.

In syslog-ng OSE version 4.2 and earlier, this option was called qout-size().

prealloc()

Type:	yes/no
Default:	no

Description: By default, syslog-ng OSE doesn’t reserve the disk space for the disk-buffer file, since in a properly configured and sized environment the disk-buffer is practically empty, so a large preallocated disk-buffer file is just a waste of disk space. But a preallocated buffer can prevent other data from using the intended buffer space (and elicit a warning from the OS if disk space is low), preventing message loss if the buffer is actually needed. To avoid this problem, when using syslog-ng OSE 4.0 or later, you can preallocate the space for your disk-buffer files by setting prealloc(yes).

In addition to making sure that the required disk space is available when needed, preallocated disk-buffer files provide radically better (3-4x) performance as well: in case of an outage the amount of messages stored in the disk-buffer is continuously growing, and using large continuous files is faster, than constantly waiting on a file to change its size.

If you are running syslog-ng OSE on a dedicated host (always recommended for any high-volume settings), use prealloc(yes).

Available in syslog-ng OSE 4.0 and later.

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.

truncate-size-ratio()

Type:	number((between 0 and 1))
Default:	1 (do not truncate)

Description: Limits the truncation of the disk-buffer file. Truncating the disk-buffer file can slow down the disk IO operations, but it saves disk space. By default, syslog-ng OSE version 4.0 and later doesn’t truncate disk-buffer files by default (truncate-size-ratio(1)). Earlier versions freed the disk-space when at least 10% of the disk-buffer file could be freed (truncate-size-ratio(0.1)).

syslog-ng OSE only truncates the file if the possible disk gain is more than truncate-size-ratio() times capacity-bytes().

Smaller values free disk space quicker.
Larger ratios result in better performance.

If you want to avoid performance fluctuations:

use truncate-size-ratio(1) (never truncate), or
use prealloc(yes) to reserve the entire size of the disk-buffer on disk.

CAUTION: It is not recommended to change truncate-size-ratio(). Only change its value if you understand the performance implications of doing so.

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(
                flow-control-window-bytes(10000)
                capacity-bytes(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(
                flow-control-window-size(10000)
                capacity-bytes(2000000)
                reliable(no)
                dir("/tmp/disk-buffer")
            )
        );
    };

fallback()

Type:	string or template
Default:	'${MSG} - host: ${HOST} \| program: ${PROGRAM}(${PID}) \| severity: ${PRIORITY}'

Description: The plain-text summary of the Slack attachment. For details, see the fallback option in the Slack documentation.

Type:	URL
Default:	string or template

Description: The footer of the message. For details, see the footer option in the Slack documentation.

Type:	URL
Default:	None

Description: A hyperlink for an image. For details, see the footer_icon option in the Slack documentation.

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")
        )
      );
};

hook-url()

Type:	URL
Default:	None

Description: The Webhook URL for the Incoming Webhook of your Slack app. This URL must also include the authentication token that syslog-ng OSE uses to authenticate to Slack. For example: https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX

For details, see the Slack webhook documentation.

image-url()

Type:	URL
Default:	None

Description: A hyperlink for an image. For details, see the image_url option in the Slack API documentation.

log-fifo-size()

Type:	number
Default:	Use global setting.

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

persist-name()

Type:	string
Default:	N/A

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.

Automatic assignment of persist names failed, as conflicting persist names were found. Please override the automatically assigned identifier using an explicit persist-name() option or remove the duplicated configuration elements.

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”).

pretext()

Type:	string or template
Default:	None

Description: The text that appears above the attachment block. For details, see the pretext option in the Slack API documentation.

retries()

Type:	number (of attempts)
Default:	3

Description: If syslog-ng OSE cannot send a message, it will try again until the number of attempts reaches retries().

If the number of attempts reaches retries(), syslog-ng OSE will wait for time-reopen() time, then tries sending the message again.

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.

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 OSE 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.

thumb-url()

Type:	URL
Default:	None

Description: A hyperlink for a thumbnail image. For details, see the thumb_url option in the Slack API documentation.

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.

title()

Type: string or template

Default: None

Description: The message title in Slack. For details, see the title option in the Slack API documentation.

title-link()

Type:	URL
Default:	None

Description: A hyperlink for the message title in Slack. For details, see the title_link option in the Slack API documentation.

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.

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.