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Best practices and examples

This chapter discusses some special examples and recommendations.

1 - General recommendations

This section provides general tips and recommendations on using syslog-ng. Some of the recommendations are detailed in the sections below:

  • Do not base the separation of log messages in different files on the facility parameter. As several applications and processes can use the same facility, the facility does not identify the application that sent the message. By default, the facility parameter is not even included in the log message itself. In general, sorting the log messages into several different files can make finding specific log messages difficult. If you must create separate log files, use the application name.

  • Standard log messages include the local time of the sending host, without any time zone information. It is recommended to replace this timestamp with an ISODATE timestamp, because the ISODATE format includes the year and timezone as well. To convert all timestamps to the ISODATE format, include the following line in the syslog-ng.conf configuration file:

        options {ts-format(iso) ; };

  • Resolving the IP addresses of the clients to domain names can decrease the performance. For details, see Using name resolution in syslog-ng.

2 - Handling large message load

This section provides tips on optimizing the performance of syslog-ng. Optimizing the performance is important for AxoSyslog hosts that handle large traffic.

  • Disable DNS resolution, or resolve hostnames locally. For details, see Using name resolution in syslog-ng.

  • Enable flow-control for the TCP sources. For details, see Managing incoming and outgoing messages with flow-control.

  • Do not use the usertty() destination driver. Under heavy load, the users are not be able to read the messages from the console, and it slows down syslog-ng.

  • Do not use regular expressions in our filters. Evaluating general regular expressions puts a high load on the CPU. Use simple filter functions and logical operators instead. For details, see Regular expressions.

  • Increase the value of the flush-lines() parameter. Increasing flush-lines() from 0 to 100 can increase the performance of AxoSyslog by 100%.

3 - Using name resolution in syslog-ng

The AxoSyslog application can resolve the hostnames of the clients and include them in the log messages. However, the performance of AxoSyslog is severely degraded if the domain name server is unaccessible or slow. Therefore, it is not recommended to resolve hostnames in syslog-ng. If you must use name resolution from syslog-ng, consider the following:

  • Use DNS caching. Verify that the DNS cache is large enough to store all important hostnames. (By default, the AxoSyslog DNS cache stores 1007 entries.)

        options { dns-cache-size(2000); };

  • If the IP addresses of the clients change only rarely, set the expiry of the DNS cache large.

        options { dns-cache-expire(87600); };

  • If possible, resolve the hostnames locally. For details, see Resolving hostnames locally.

3.1 - Resolving hostnames locally

Purpose:

Resolving hostnames locally enables you to display hostnames in the log files for frequently used hosts, without having to rely on a DNS server. The known IP address - hostname pairs are stored locally in a file. In the log messages, AxoSyslog will replace the IP addresses of known hosts with their hostnames. To configure local name resolution, complete the following steps:

Steps:

  1. Add the hostnames and the respective IP addresses to the file used for local name resolution. On Linux and UNIX systems, this is the /etc/hosts file. Consult the documentation of your operating system for details.

  2. Instruct AxoSyslog to resolve hostnames locally. Set the use-dns() option to persist_only.

  3. Set the dns-cache-hosts() option to point to the file storing the hostnames.

        options {
        use-dns(persist_only);
        dns-cache-hosts(/etc/hosts);
    };

4 - Collecting logs from chroot

Purpose:

To collect logs from a chroot using an AxoSyslog client running on the host, complete the following steps:

Collecting logs from chroot

Steps:

  1. Create a /dev directory within the chroot. The applications running in the chroot send their log messages here.

  2. Create a local source in the configuration file of the AxoSyslog application running outside the chroot. This source should point to the /dev/log file within the chroot (for example, to the /chroot/dev/log directory).

  3. Include the source in a log statement.

5 - Configuring log rotation

The AxoSyslog application does not rotate logs by itself. To use AxoSyslog for log rotation, consider the following approaches:

Use logrotate together with AxoSyslog:

  • It is ideal for workstations or when processing fewer logs.

  • It is included in most distributions by default.

  • Less scripting is required, only logrotate has to be configured correctly.

  • Requires frequent restart (AxoSyslog must be reloaded/restarted when the files are rotated). After rotating the log files, reload AxoSyslog using the syslog-ng-ctl reload command, or use another method to send a SIGHUP to AxoSyslog.

  • The statistics collected by AxoSyslog, and the correlation information gathered with Pattern Database, are lost with each restart.

Separate incoming logs based on time, host or other information:

  • It is ideal for central log servers, where regular restart of AxoSyslog is unfavorable.

  • Requires shell scripts or cron jobs to remove old logs.

  • It can be done by using macros in the destination name (in the filename, directory name, or the database table name). (For details on using macros, see Templates and macros.)

Example: File destination for log rotation

This sample file destination configuration stores incoming logs in files that are named based on the current year, month and day, and places these files in directories that are named based on the hostname:

   destination d_sorted {
        file(
            "/var/log/remote/${HOST}/${YEAR}_${MONTH}_${DAY}.log"
            create-dirs(yes)
        );
    };

Example: Logstore destination for log rotation

This sample logstore destination configuration stores incoming logs in logstores that are named based on the current year, month and day, and places these logstores in directories that are named based on the hostname:

   destination d_logstore {
        logstore(
            "/var/log/remote/${HOST}/${YEAR}_${MONTH}_${DAY}.lgs"
            compress(9)
            create-dirs(yes)
        );
    };

Example: Command for cron for log rotation

This sample command for cron removes files older than two weeks from the /var/log/remote directory:

   find /var/log/remote/ -daystart -mtime +14 -type f -exec rm {} \;

6 - Load balancing logs between multiple destinations

These sections describe a method of load balancing logs between multiple AxoSyslog destinations. The first subsection describes the round robin load balancing method based on the R_MSEC macro of AxoSyslog, while the second subsection describes a configuration generator that you can use as an alternative to using the example configuration described in the first subsection.

For more information about the R_MSEC macro and further macros of AxoSyslog, see Macros of AxoSyslog.

6.1 - Load balancing with a round robin load balancing method based on the R_MSEC macro of syslog-ng OSE

This section describes a round robin load balancing method based on the R_MSEC macro of AxoSyslog to load balance your logs between multiple AxoSyslog destinations.

For more information about the R_MSEC macro and further macros of AxoSyslog, see Macros of AxoSyslog.

Example: round robin load balancing between multiple destinations

The following example is a round-robin load balancing method, based on AxoSyslog’s R_MSEC macro.

   destination d_lb_network { 
      channel { 
        channel { 
          filter { 
          "0" == "$(% ${R_MSEC} 2)" 
          }; 
          destination { 
            network("myhost1" 
              disk-buffer(flow-control-window-size(10000) capacity-bytes(2000000))); 
          }; 
          flags(final); 
        }; 
     
        channel { 
        filter { 
        "1" == "$(% ${R_MSEC} 2)" 
        }; 
    
        destination { 
          network("myhost2" 
            disk-buffer(flow-control-window-size(10000) capacity-bytes(2000000))); 
        }; 
        flags(final); 
        }; 
      }; 
    };

The filter {" <return value >" == "$(% ${R_MSEC} 2)"}; code snippets (in bold) serve as the basis of the method. This filter separates incoming log messages’ timestamp values based on the R_MSEC macro, using a division with remainder method, and distributes the log messages equally between two destinations based on the return value (in this case, 0 or 1).

If you need a file instead of a network destination, replace the network destination with the file in the example (and use the same analogy for any other AxoSyslog destinations).

For an alternative method to use the round robin load balancing method based on the R_MSEC macro, see Configuration generator for the load balancing method based on MSEC hashing.

6.2 - Configuration generator for the load balancing method based on MSEC hashing

This section describes a configuration generator for the load balancing method based on MSEC hashing to load balance your logs between multiple AxoSyslog destinations.

As an alternative to using the example configuration described in Load balancing with a round robin load balancing method based on the R_MSEC macro of syslog-ng OSE, a configuration generator script is also available in AxoSyslog:

   destination d_lb {network-load-balancer(targets(myhost1 myhost2 myhost3))};

Where destinations share the same configuration except for the destination address, balancing is based on MSEC hashing.