syslog-ng Open Source Edition 3.22 - Administration Guide

python: writing custom Python destinations

The Python destination allows you to write your own destination in Python. You can import external Python modules to process the messages, and send them to other services or servers. Since many services have a Python library, the Python destination makes integrating syslog-ng OSE very easy and quick.

The following points apply to using Python blocks in syslog-ng OSE in general.

• Python parsers and template functions are available in syslog-ng OSE version 3.10 and later.

  Python destinations and sources are available in syslog-ng OSE version 3.18 and later.

• Supported Python versions: 2.7 and 3.4+ (if you are using pre-built binaries, check the dependencies of the package to find out which Python version it was compiled with)

• The Python block must be a top-level block in the syslog-ng OSE configuration file.

• If you store the Python code in a separate Python file and only include it in the syslog-ng OSE configuration file, make sure that the PYTHON_PATH environment variable includes the path to the Python file, and export the PYTHON_PATH environment variable. For example, if you start syslog-ng OSE manually from a terminal and you store your Python files in the /opt/syslog-ng/etc directory, use the following command: export PYTHONPATH=/opt/syslog-ng/etc

  In production, when syslog-ng OSE starts on boot, you must configure your startup script to include the Python path. The exact method depends on your operating system. For recent Red Hat Enterprise Linux, Fedora, and CentOS distributions that use systemd, the systemctl command sources the /etc/sysconfig/syslog-ng file before starting syslog-ng OSE. (On openSUSE and SLES, /etc/sysconfig/syslog file.) Append the following line to the end of this file: PYTHONPATH="<path-to-your-python-file>", for example, PYTHONPATH="/opt/syslog-ng/etc"

• The Python object is initiated every time when syslog-ng OSE is started or reloaded.

  Caution: If you reload syslog-ng OSE, existing Python objects are destroyed, therefore the context and state information of Python blocks is lost. Log rotation and updating the configuration of syslog-ng OSE typically involves a reload.

• The Python block can contain multiple Python functions.

• Using Python code in syslog-ng OSE can significantly decrease the performance of syslog-ng OSE, especially if the Python code is slow. In general, the features of syslog-ng OSE are implemented in C, and are faster than implementations of the same or similar features in Python.

• Validate and lint the Python code before using it. The syslog-ng OSE application does not do any of this.

• Python error messages are available in the internal() source of syslog-ng OSE.

• You can access the name-value pairs of syslog-ng OSE directly through a message object or a dict.

• To help debugging and troubleshooting your Python code, you can send log messages to the internal() source of syslog-ng OSE. For details, see Logging from your Python code.

destination <name_of_the_python_destination>{
    python(
        class("<name_of_the_python_class_executed_by_the_destination>")
    );
};

python {
class <name_of_the_python_class_executed_by_the_destination>(object):

    def open(self):
        """Open a connection to the target service

        Should return False if opening fails"""
        return True

    def close(self):
        """Close the connection to the target service"""
        pass

    def is_opened(self):
        """Check if the connection to the target is able to receive messages"""
        return True

    def init(self, options):
        """This method is called at initialization time

        Should return false if initialization fails"""
        return True

    def deinit(self):
        """This method is called at deinitialization time"""
        pass

    def send(self, msg):
        """Send a message to the target service

        It should return True to indicate success. False will suspend the
        destination for a period specified by the time-reopen() option."""
        return True

    def flush(self):
        """Flush the queued messages"""
        pass
};

destination d_python_to_file {
    python(
        class("TextDestination")
    );
};
log {
    source(src);
    destination(d_python_to_file);
};
python {
class TextDestination(object):
    def send(self, msg):
        self.outfile = open("/tmp/example.txt", "a")
        self.outfile.write("MESSAGE = %s\n" % msg["MESSAGE"])
        self.outfile.flush()
        self.outfile.close();
        return True
};

destination d_python_to_file {
    python(
        class("TextDestination")
    );
};
log {
    source(src);
    destination(d_python_to_file);
};
python {
class TextDestination(object):
    def open(self):
        try:
            self.outfile = open("/tmp/example.txt", "a")
            return True
        except:
            return False

    def send(self, msg):
        self.outfile.write("MESSAGE = %s\n" % msg["MESSAGE"])
        self.outfile.flush()
        return True

    def close(self):
        try:
            self.outfile.flush()
            self.outfile.close();
            return True
        except:
            return False
};

class MyDestination(object):
    def init(self, options):
        self.bulk = list()
        return True

    def send(self, msg):
         self.bulk.append(msg["MSG"].decode())
         return self.QUEUED

    def flush(self):
        print("flushing: " + ",".join(self.bulk))
        self.bulk = list()
        return self.SUCCESS

For the list of available optional parameters, see python() destination options.

python() destination options

The Python destination allows you to write your own destination in Python. The python() destination has the following options. The class() option is mandatory. For details on writing destinations in Python, see python: writing custom Python destinations.

python(
    class("MyPythonDestination")
);

python(
    class("MyPythonfilename.MyPythonDestination")
);

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:

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

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")
        )
    );
};

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")
        )
    );
};

frac-digits()

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.

python(class(usermodule.HyParser) loaders(hy))

log-fifo-size()

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

on-error()

Description: Controls what happens when type-casting fails and syslog-ng OSE cannot convert some data to the specified type. By default, syslog-ng OSE 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 OSE.

• 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.

python(
    class("MyPythonClass")
    options(
        "host" "127.0.0.1"
        "port" "1883"
        "otheroption" "value")
);

persist-name()

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").

throttle()

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.

scope("selected-macros" "nv-pairs")

destination d_python_to_file {
    python(
        class("pythonexample.TextDestination")
        value-pairs(key(MESSAGE))
    );
};

redis: Storing name-value pairs in Redis

The redis() driver sends messages as name-value pairs to a Redis key-value store.

For the list of available parameters, see redis() destination options.

Declaration:

redis(
    host("<redis-server-address>")
    port("<redis-server-port>")
    auth("<redis-server-password>") # Optional, for password-protected servers
    command("<redis-command>", "<first-command-parameter>", "<second-command-parameter>", "<third-command-parameter>")
);

destination d_redis {
    redis(
        host("localhost")
        port(6379)
        command("HINCRBY", "hosts", "$HOST", "1")
    );
};

@version: 3.22

source s_apache {
    file("/var/log/apache2/access.log");
};

parser p_apache {
    csv-parser(columns("APACHE.CLIENT_IP", "APACHE.IDENT_NAME", "APACHE.USER_NAME",
                    "APACHE.TIMESTAMP", "APACHE.REQUEST_URL", "APACHE.REQUEST_STATUS",
                    "APACHE.CONTENT_LENGTH", "APACHE.REFERER", "APACHE.USER_AGENT",
                    "APACHE.PROCESS_TIME", "APACHE.SERVER_NAME")
                flags(escape-double-char,strip-whitespace)
    delimiters(" ")
    quote-pairs('""[]')
    );
};

destination d_redis {
    redis( command("HINCRBY" "${MONTH_ABBREV} ${DAY} ${HOUR}:${MIN}"  "${APACHE.USER_AGENT}" "1"));
};

log {
    source(s_apache);
    parser(p_apache);
    destination(d_redis);
};

redis() destination options

The redis() driver sends messages as name-value pairs to a Redis key-value store.

The redis() destination has the following options:

auth()

Description: The password used for authentication on a password-protected Redis server. Available in syslog-ng OSE version 3.10 and later.

command()

Description: The Redis command to execute, for example, LPUSH, INCR, or HINCRBY. Using the HINCRBY command with an increment value of 1 allows you to create various statistics. For example, the command("HINCRBY" "${HOST}/programs" "${PROGRAM}" "1") command counts the number of log messages on each host for each program.

Note the following points when using the redis() destination:

• You can use macros and templates in the parameters of the Redis command.

• Currently you can use only one command in a redis() destination.

• The syslog-ng OSE application ignores the return value of the command. If the Redis server returns an error, syslog-ng OSE closes the connection.

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:

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

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")
        )
    );
};

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")
        )
    );
};

batch-lines()

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.

batch-timeout()

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.

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.

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:

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:

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

host()

Description: The hostname or IP address of the Redis server.

port()

Description: The port number of the Redis server.

retries()

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.

throttle()

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.