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syslog-ng Premium Edition 7.0.12 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng PE quick-start guide The syslog-ng PE configuration file Collecting log messages — sources and source drivers
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 network: Collecting messages using the RFC3164 protocol (network() driver) osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes 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 unix-stream, unix-dgram: Collecting messages from UNIX domain sockets windowsevent: Collecting Windows event logs
Sending and storing log messages — destinations and destination drivers
elasticsearch: Sending messages directly to Elasticsearch version 1.x elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher file: Storing messages in plain-text files hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka: Publishing messages to Apache Kafka logstore: Storing messages in encrypted files mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) pipe: Sending messages to named pipes program: Sending messages to external applications python: writing custom Python destinations smtp: Generating SMTP messages (e-mail) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql: Storing messages in an SQL database syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng: Forwarding messages and tags 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) unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal — usertty() destination Client-side failover
Routing messages: log paths, flags, and filters Global options of syslog-ng PE TLS-encrypted message transfer Advanced Log Transfer Protocol Reliability and minimizing the loss of log messages Manipulating messages parser: Parse and segment structured messages Processing message content with a pattern database Correlating log messages Enriching log messages with external data Monitoring statistics and metrics of syslog-ng Multithreading and scaling in syslog-ng PE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages About us

Configuring flow-control

For details on how flow-control works, see Managing incoming and outgoing messages with flow-control. The summary of the main points is as follows:

  • The syslog-ng application normally reads a maximum of log-fetch-limit() number of messages from a source.

  • From TCP and unix-stream sources, syslog-ng reads a maximum of log-fetch-limit() from every connection of the source. The number of connections to the source is set using the max-connections() parameter.

  • Every destination has an output buffer (log-fifo-size()).

  • Flow-control uses a control window to determine if there is free space in the output buffer for new messages. Every source has its own control window, the log-iw-size() parameter sets the size of the control window.

  • When a source accepts multiple connections, the size of the control window is divided by the value of the max-connections() parameter and this smaller control window is applied to each connection of the source.

  • The output buffer must be larger than the control window of every source that logs to the destination.

  • If the control window is full, syslog-ng stops reading messages from the source until some messages are successfully sent to the destination.

  • If the output buffer becomes full, and neither disk-buffering nor flow-control is used, messages may be lost.

Caution:

If you modify the max-connections() or the log-fetch-limit() parameter, do not forget to adjust the log-iw-size() and log-fifo-size() parameters accordingly.

Example: Sizing parameters for flow-control

Suppose that syslog-ng has a source that must accept up to 300 parallel connections. Such situation can arise when a network source receives connections from many clients, or if many applications log to the same socket.

Set the max-connections() parameter of the source to 300. However, the log-fetch-limit() (default value: 10) parameter applies to every connection of the source individually, while the log-iw-size() (default value: 1000) parameter applies to the source. In a worst-case scenario, the destination does not accept any messages, while all 300 connections send at least log-fetch-limit() number of messages to the source during every poll loop. Therefore, the control window must accommodate at least max-connections()*log-fetch-limit() messages to be able to read every incoming message of a poll loop. In the current example this means that log-iw-size() should be greater than 300*10=3000. If the control window is smaller than this value, the control window might fill up with messages from the first connections — causing syslog-ng to read only one message of the last connections in every poll loop.

The output buffer of the destination must accommodate at least log-iw-size() messages, but use a greater value: in the current example 3000*10=30000 messages. That way all incoming messages of ten poll loops fit in the output buffer. If the output buffer is full, syslog-ng does not read any messages from the source until some messages are successfully sent to the destination.

source s_localhost {
            network(ip(127.0.0.1) port(1999) max-connections(300)); };
destination d_tcp {
            network("10.1.2.3" port(1999) localport(999) log-fifo-size(30000)); };
log { source(s_localhost); destination(d_tcp); flags(flow-control); };

If other sources send messages to this destination, than the output buffer must be further increased. For example, if a network host with maximum 100 connections also logs into the destination, than increase the log-fifo-size() by 10000.

source s_localhost {
            network(ip(127.0.0.1) port(1999) max-connections(300)); };
source s_tcp {
            network(ip(192.168.1.5) port(1999) max-connections(100)); };
destination d_tcp {
            network("10.1.2.3" port(1999) localport(999) log-fifo-size(40000)); };
log { source(s_localhost); destination(d_tcp); flags(flow-control); };

Using disk-based and memory buffering

The syslog-ng Premium Edition application can store messages on the local hard disk if the destination (for example, the central log server) or the network connection to the destination becomes unavailable. The syslog-ng PE application automatically sends the stored messages to the destination when the connection is reestablished. The disk buffer is used as a queue: when the connection to the destination is reestablished, syslog-ng PE sends the messages to the destination in the order they were received.

NOTE:

Disk-based buffering can be used in conjunction with flow-control. For details on flow-control, see Managing incoming and outgoing messages with flow-control.

The following destination drivers can use disk-based buffering: elasticsearch2(), file(), hdfs(), kafka(), mongodb(), program(), riemann(), smtp(),sql(), unix-dgram(), and unix-stream(). The network(), syslog(), tcp(), and tcp6() destination drivers can also use disk-based buffering, except when using the udp transport method. (The other destinations or protocols do not provide the necessary feedback mechanisms required for disk-based buffering.)

Every such destination uses a separate disk buffer (similarly to the output buffers controlled by log-fifo-size()). The hard disk space is not pre-allocated, so ensure that there is always enough free space to store the disk buffers even when the disk buffers are full.

If syslog-ng PE is restarted (using the /etc/init.d/syslog-ng restart command, or another appropriate command on your platform), it automatically saves any unsent messages from the disk buffer and the output queue. After the restart, syslog-ng PE sends the saved messages to the destination. In other words, the disk buffer is persistent. The disk buffer is also resistant to syslog-ng PE crashes.

The syslog-ng PE application supports two types of disk buffering: reliable and normal. For details, see Enabling reliable disk-based buffering and Enabling normal disk-based buffering, respectively.

Message handling and normal disk-based buffering

When you use disk-based buffering, and the reliable() option is set to no, syslog-ng PE handles outgoing messages the following way:

Figure 31: Handling outgoing messages in syslog-ng PE

  • Output queue: Messages from the output queue are sent to the destination (for example, your central log server). The syslog-ng PE application puts the outgoing messages directly into the output queue, unless the output queue is full. By default, the output queue can hold 64 messages (you can adjust it using the quot-size() option).

  • Disk buffer: If the output queue is full, disk-buffering is enabled, and reliable() is set to no, syslog-ng PE puts the outgoing messages into the disk buffer of the destination. (The disk buffer is enabled if the disk-buffer() option is configured.)

  • Overflow queue: If the output queue is full and the disk buffer is disabled or full, syslog-ng PE puts the outgoing messages into the overflow queue of the destination. (The overflow queue is identical to the output buffer used by other destinations.) The log-fifo-size() parameter specifies the number of messages stored in the overflow queue. For details on sizing the log-fifo-size() parameter, see also Managing incoming and outgoing messages with flow-control.

NOTE:

Using disk buffer can significantly decrease performance.

Message handling and reliable disk-based buffering

When you use disk-based buffering, and the reliable() option is set to yes, syslog-ng PE handles outgoing messages the following way.

The mem-buf-size() option determines when flow-control is triggered. All messages arriving to the log path that includes the destination using the disk-buffer are written into the disk-buffer, until the size of the disk-buffer reaches (disk-buf-size() minus mem-buf-size()). Above that size, messages are written into both the disk-buffer and the memory-buffer, indicating that flow-control needs to slow down the message source. These messages are not taken out from the control window (governed by log-iw-size()), causing the control window to fill up. If the control window is full, the flow-control completely stops reading incoming messages from the source.

(As a result, mem-buf-size() must be at least as large as log-iw-size().)

Enabling reliable disk-based buffering

The following destination drivers can use disk-based buffering: elasticsearch2(), file(), hdfs(), kafka(), mongodb(), program(), riemann(), smtp(),sql(), unix-dgram(), and unix-stream(). The network(), syslog(), tcp(), and tcp6() destination drivers can also use disk-based buffering, except when using the udp transport method. (The other destinations or protocols do not provide the necessary feedback mechanisms required for disk-based buffering.)

To enable reliable disk-based buffering, use the disk-buffer(reliable(yes)) parameter in the destination. Use reliable disk-based buffering if you do not want to lose logs in case of reload/restart, unreachable destination or syslog-ng PE crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. The filename of the reliable disk buffer file is the following: <syslog-ng path>/var/syslog-ng-00000.rqf.

Example: Example for using reliable disk-based buffering
destination d_BSD {
    network(
            "127.0.0.1"
            port(3333)
            disk-buffer(
                mem-buf-size(10000)
                disk-buf-size(2000000)
                reliable(yes)
            )
        );
}; 

For details on the differences between normal and reliable disk-based buffering, see also About disk queue files.

Enabling normal disk-based buffering

The following destination drivers can use disk-based buffering: elasticsearch2(), file(), hdfs(), kafka(), mongodb(), program(), riemann(), smtp(),sql(), unix-dgram(), and unix-stream(). The network(), syslog(), tcp(), and tcp6() destination drivers can also use disk-based buffering, except when using the udp transport method. (The other destinations or protocols do not provide the necessary feedback mechanisms required for disk-based buffering.)

To enable normal disk-based buffering, use the disk-buffer(reliable(no)) parameter in the destination. Use normal disk-based buffering if you want a solution that is faster than the reliable disk-based buffering. In this case, disk buffering will be less reliable and it is possible to lose logs in case of syslog-ng PE crash. The filename of the normal disk buffer file is the following: <syslog-ng path>/var/syslog-ng-00000.qf.

Example: Example for using normal disk-based buffering

When using the disk-buffer plugin

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

For details on the differences between normal and reliable disk-based buffering, see also About disk queue files.

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