Managing complex configurations

• 1: Including configuration files
• 2: Reusing configuration blocks
• 3: Generating configuration blocks from a script

1 - Including configuration files

The AxoSyslog application supports including external files in its configuration file, so parts of its configuration can be managed separately. To include the contents of a file in the AxoSyslog configuration, use the following syntax:

   @include "<filename>"

This imports the entire file into the configuration of AxoSyslog, at the location of the include statement. The <filename> can be one of the following:

• A filename, optionally with full path. The filename (not the path) can include UNIX-style wildcard characters (*, ?). When using wildcard characters, AxoSyslog will include every matching file. For details on using wildcard characters, see Types and options of regular expressions.

• A directory. When including a directory, AxoSyslog will try to include every file from the directory, except files beginning with a ~ (tilde) or a . (dot) character. Including a directory is not recursive. The files are included in alphabetic order, first files beginning with uppercase characters, then files beginning with lowercase characters. For example, if the directory contains the a.conf, B. conf, c.conf, D.conf files, they will be included in the following order: B.conf, D. conf, a.conf, c.conf.

When including configuration files, consider the following points:

• The default path where AxoSyslog looks for the file depends on where AxoSyslog is installed. The syslog-ng --version command displays this path as Include-Path.

• Defining an object twice is not allowed, unless you use the @define allow-config-dups 1 definition in the configuration file. If an object is defined twice (for example, the original configuration file and the file imported into this configuration file both define the same option, source, or other object), then the object that is defined later in the configuration file will be effective. For example, if you set a global option at the beginning of the configuration file, and later include a file that defines the same option with a different value, then the option defined in the imported file will be used.

  • Files can be embedded into each other: the included files can contain include statements as well, up to a maximum depth of 15 levels.

  • You cannot include complete configuration files into each other, only configuration snippets can be included. This means that the included file cannot have a @version statement.

  • Include statements can only be used at top level of the configuration file. For example, the following is correct:

        @version: 4.10.0
        @include "example.conf"
    

    But the following is not:

        source s_example {
            @include "example.conf"
        };
    

2 - Reusing configuration blocks

To create a reusable configuration snippet and reuse parts of a configuration file, you have to define the block (for example, a source) once, and reference it later. Any AxoSyslog object can be a block. Use the following syntax to define a block:

   block type name() {<contents of the block>};

Type must be one of the following: destination, filter, log, options, parser, rewrite, root, source. The root blocks can be used in the “root” context of the configuration file, that is, outside any other statements.

Note that options can be used in blocks only in version 3.22 and later.

Blocks may be nested into each other, so for example, a block can be built from other blocks. Blocks are somewhat similar to C++ templates.

The type and name combination of each block must be unique, that is, two blocks can have the same name if their type is different.

To use a block in your configuration file, you have to do two things:

• Include the file defining the block in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version 3.7 and newer automatically includes the *.conf files from the <directory-where-syslog-ng-is-installed>/scl/*/ directories.

• Reference the name of the block in your configuration file. This will insert the block into your configuration. For example, to use a block called myblock, include the following line in your configuration:

      myblock()
  

  Blocks may have parameters, but even if they do not, the reference must include opening and closing parentheses like in the previous example.

The contents of the block will be inserted into the configuration when AxoSyslog is started or reloaded.

Example: Reusing configuration blocks

Suppose you are running an application on your hosts that logs into the /opt/var/myapplication.log file. Create a file (for example, myblocks.conf) that stores a source describing this file and how it should be read:

   block source myappsource() {
            file("/opt/var/myapplication.log" follow-freq(1) default-facility(syslog)); };

Include this file in your main syslog-ng.conf configuration file, reference the block, and use it in a logpath:

   @version: 4.10.0
    @include "<correct/path>/myblocks.conf"
    source s_myappsource { myappsource(); };
    ...
    log { source(s_myappsource); destination(...); };

To define a block that defines more than one object, use root as the type of the block, and reference the block from the main part of the AxoSyslog configuration file.

Example: Defining blocks with multiple elements

The following example defines a source, a destination, and a log path to connect them.

   block root mylogs() {
        source s_file {
            file("/var/log/mylogs.log" follow-freq(1));
        };
        destination d_local {
            file("/var/log/messages");
        };
        log {
            source(s_file); destination(d_local);
        };
    };

Mandatory parameters

You can express in block definitons that a parameter is mandatory by defining it with empty brackets (). In this case, the parameter must be overridden in the reference block. Failing to do so will result in an error message and initialization failure.

To make a parameter expand into nothing (for example, because it has no default value, like hook-commands() or tls()), insert a pair of double quote marks inside the empty brackets: ("")

Example: Mandatory parameters

The following example defines a TCP source that can receive the following parameters: the port where AxoSyslog listens (localport), and optionally source flags (flags).

   block source my_tcp_source(localport() flags("")) {
        network(port(`localport`) transport(tcp) flags(`flags`));
    };

Because localport is defined with empty brackets (), it is a mandatory parameter. However, the flags parameter is not mandatory, because it is defined with an empty double quote bracket pair (""). If you do not enter a specific value when referencing this parameter, the value will be an empty string. This means that in this case

   my_tcp_source(localport(8080))

will be expanded to:

   network(port(8080) transport(tcp) flags());

Passing arguments to configuration blocks

Configuration blocks can receive arguments as well. The parameters the block can receive must be specified when the block is defined, using the following syntax:

   block type block_name(argument1(<default-value-of-the-argument>) argument2(<default-value-of-the-argument>) argument3())

If an argument does not have a default value, use an empty double quote bracket pair ("") after the name of the argument. To refer the value of the argument in the block, use the name of the argument between backticks, for example:

`argument1`

Example: Passing arguments to blocks

The following sample defines a file source block, which can receive the name of the file as a parameter. If no parameter is set, it reads messages from the /var/log/messages file.

   block source s_logfile (filename("messages")) {
        file("/var/log/`filename`" );
    };
    
    source s_example {
        s_logfile(filename("logfile.log"));
    };

If you reference the block with more arguments then specified in its definition, you can use these additional arguments as a single argument-list within the block. That way, you can use a variable number of optional arguments in your block. This can be useful when passing arguments to a template, or optional arguments to an underlying driver.

The three dots (…) at the end of the argument list refer to any additional parameters. It tells AxoSyslog that this macro accepts __VARARGS__, therefore any name-value pair can be passed without validation. To reference this argument-list, insert __VARARGS__ to the place in the block where you want to insert the argument-list. Note that you can use this only once in a block.

The following definition extends the logfile block from the previous example, and passes the optional arguments (follow-freq(1) flags(no-parse)) to the file() source.

   block source s_logfile(filename("messages") ...) {
        file("/var/log/`filename`" `__VARARGS__`);
    };
    
    source s_example {
        s_logfile(
            filename("logfile.log")
            follow-freq(1)
            flags(no-parse)
        );
    };

Example: Using arguments in blocks

The following example is the code of the pacct() source driver, which is actually a block that can optionally receive two arguments.

   block source pacct(file("/var/log/account/pacct") follow-freq(1) ...) {
        file("`file`" follow-freq(`follow-freq`) format("pacct") tags(".pacct") `__VARARGS__`);
    };

Example: Defining global options in blocks

The following example defines a block called setup-dns() to set DNS-related settings at a single place.

   block options setup-dns(use-dns()) {
        keep-hostname(no);
        use-dns(`use-dns`);
        use-fqdn(`use-dns`);
    dns-cache(`use-dns`);
    };
    
    options {
        setup-dns(use-dns(yes));
    };

3 - Generating configuration blocks from a script

Purpose:

The AxoSyslog application can automatically execute scripts when it is started, and can include the output of such script in the configuration file. To create and use a script that generates a part of the AxoSyslog configuration file (actually, a configuration block), complete the following steps. The steps include examples for collecting Apache access log files (access.log) from subdirectories, but you can create any script that creates a valid AxoSyslog configuration snippet.

Steps:

1. Navigate to the directory where you have installed AxoSyslog (for example, /opt/syslog-ng/share/include/scl/), and create a new directory, for example, apache-access-logs. The name of the directory will be used in the AxoSyslog configuration file as well, so use a descriptive name.

2. Create a file called plugin.conf in this new directory.

3. Edit the plugin.conf file and add the following line:

       @module confgen context(source) name(<directory-name>) exec("`scl-root`/<directory-name>/<my-script>")
   

   Replace <directory-name> with the name of the directory (for example, apache-access-logs), and <my-script> with the filename of your script (for example, apache-access-logs.sh). You can reference the script in your AxoSyslog configuration file as a configuration block using the value name option.

   The context option determines the type of the configuration snippet that the script generates, and must be one of the following: destination, filter, log, parser, rewrite, root, source. The root blocks can be used in the “root” context of the configuration file, that is, outside any other statements. In the example, context(source) means that the output of the script will be used within a source statement.

   You can pass parameters to the script. In the script these parameters are available as environment variables, and have the confgen_ prefix. For example, passing the --myparameter parameter becomes available in the script as the confgen_myparameter environment variable.

4. Write a script that generates the output you need, and formats it to a configuration snippet that AxoSyslog can use. The filename of the script must match with the filename used in plugin.conf, for example, apache-access-logs.sh.

   The following example checks the /var/log/apache2/ directory and its subdirectories, and creates a source driver for every directory that contains an access.log file.

       #!/bin/bash
       for i in `find /var/log/apache2/ -type d`; do
           echo "file(\"$i/access.log\" flags(no-parse) program-override(\"apache2\"));";
       done;
   

   The script generates an output similar to this one, where service* is the actual name of a subdirectory:

       file("/var/log/apache2/service1/access.log" flags(no-parse) program-override("apache2"));
       file("/var/log/apache2/service2/access.log" flags(no-parse) program-override("apache2"));
   

5. Include the plugin.conf file in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version 3.7 and newer automatically includes the *.conf files from the <directory-where-syslog-ng-is-installed>/scl/*/ directories. For details on including configuration files, see Including configuration files.

6. Add the block you defined in the plugin.conf file to your AxoSyslog configuration file. You can reference the block using the value of the name option from the plugin.conf file, followed by parentheses, for example, apache-access-logs(). Make sure to use the block in the appropriate context of the configuration file, for example, within a source statement if the value of the context option in the plugin.conf file is source.

       @include "scl.conf"
       ...
       source s_apache {
           file("/var/log/apache2/access.log" flags(no-parse) program-override("apache2"));
           file("/var/log/apache2/error.log" flags(no-parse) program-override("apache2"));
           file("/var/log/apache2/ssl.log" flags(no-parse) program-override("apache2"));
           apache-access-logs();
       };
   
       log {
           source(s_apache); destination(d_central);
       };
       ...
   

7. Check if your modified AxoSyslog configuration file is syntactically correct using the syslog-ng --syntax-only command.

8. If your modified configuration is syntactically correct, load the new configuration file using the syslog-ng-ctl reload command.