syslog-ng Open Source Edition 3.18 - Administration Guide

Location

/patterndb/ruleset/actions/action/create-context

Description

OPTIONAL — Creates a new correlation context from the current message and its associated context. This can be used to "split" a context.

Available in syslog-ng OSE version 3.8 and later.

Attributes

• context-id: OPTIONAL — An identifier to group related log messages when using the pattern database to correlate events. The ID can be a descriptive string describing the events related to the log message (for example, ssh-sessions for log messages related to SSH traffic), but can also contain macros to generate IDs dynamically. When using macros in IDs, see also the context-scope attribute. Starting with syslog-ng OSE version 3.5, if a message is added to a context, syslog-ng OSE automatically adds the identifier of the context to the .classifier.context_id macro of the message. For details on correlating messages, see Correlating log messages using pattern databases.

  NOTE: The syslog-ng OSE application determines the context of the message after the pattern matching is completed. This means that macros and name-value pairs created by the matching pattern database rule can be used as context-id macros.

• context-timeout: OPTIONAL — The number of seconds the context is stored. Note that for high-traffic log servers, storing open contexts for long time can require significant amount of memory. For details on correlating messages, see Correlating log messages using pattern databases.

• context-scope: OPTIONAL — Specifies which messages belong to the same context. This attribute is used to determine the context of the message if the context-id does not specify any macros. Usually, context-scope acts a filter for the context, with context-id refining the filtering if needed. The following values are available:

  • process: Only messages that are generated by the same process of a client belong to the same context, that is, messages that have identical ${HOST}, ${PROGRAM} and ${PID} values. This is the default behavior of syslog-ng OSE if context-scope is not specified.

  • program: Messages that are generated by the same application of a client belong to the same context, that is, messages that have identical ${HOST} and ${PROGRAM} values.

  • host: Every message generated by a client belongs to the same context, only the ${HOST} value of the messages must be identical.

  • global: Every message belongs to the same context.

  NOTE: Using the context-scope attribute is significantly faster than using macros in the context-id attribute.

  For details on correlating messages, see Correlating log messages using pattern databases.

Children

• message: A container element storing the message that is added to the new context when the action is executed.

  • inherit-mode: This attribute controls which name-value pairs and tags are propagated to the newly generated message.

    • context: syslog-ng OSE collects every name-value pair from each message stored in the context, and includes them in the generated message. If a name-value pair appears in multiple messages of the context, the value in the latest message will be used. Note that tags are not merged, the generated message will inherit the tags assigned to the last message of the context.

    • last-message: Only the name-value pairs appearing in the last message are copied. If the context contains only a single message, then it is the message that triggered the action.

    • none: An empty message is created, without inheriting any tags or name-value pairs.

    For details on the message context, see Correlating log messages using pattern databases and Actions and message correlation. For details on triggering messages, see Triggering actions for identified messages

<rule provider='test' id='12' class='violation'>
  <patterns>
    <pattern>simple-message-with-action-to-create-context</pattern>
  </patterns>
  <actions>
    <action trigger='match'>
      <create-context context-id='1000' context-timeout='60' context-scope='program'>
        <message inherit-properties='context'>
          <values>
            <value name='MESSAGE'>context message</value>
          </values>
        </message>
      </create-context>
    </action>
  </actions>
</rule>

Location

/patterndb/ruleset/tags

Description

OPTIONAL — An element containing custom keywords (tags) about the messages matching the patterns. The tags can be used to label specific events (for example user logons). It is also possible to filter on these tags later (for details, see Tagging messages). Starting with syslog-ng Open Source Edition 3.2, the list of tags assigned to a message can be referenced with the ${TAGS} macro.

Attributes

N/A

Children

• tag: OPTIONAL — A keyword or tags applied to messages matching the rule.

<tags><tag>UserLogin</tag></tags>

How the grouping-by() parser works

    +--------------------+
    |Incoming log message|
    +--------------------+
              |
              |
              |
              |
              V
    +-------------------------------------------+    No
    |Does it match key(), scope(), and where()? +----------> Ignore message
    +-------------------------------------------+
              |
              |
              V
    Add message to context
              |
              |
              v                    No
    Is it a trigger() message or --------> Wait until timeout() or a new message
    has the timeout() expired?
             +
             |
             |
             v                              No
    Does the context match having()? +-------------> Close the context
            +                                         and do nothing
            |
            |
            v
    Inject the aggregate() log message and close the context
    

The grouping-by() parser has three options that determine if a message is added to a context: scope(), key(), and where().

• The scope() option acts as an early filter, selecting messages sent by the same process (${HOST}${PROGRAM}${PID} is identical), application (${HOST}${PROGRAM} is identical), or host.

• The key() identifies the context the message belongs to. (The value of the key must be the same for every message of the context.)

• To use a filter to further limit the messages that are added to the context, you can use the where() option.

The timeout() option determines how long a context is stored, that is, how long syslog-ng OSE waits for related messages to arrive. If the group has a specific log message that ends the context (for example, a logout message), you can specify it using the trigger() option.

When the context is closed, and the messages match the filter set in the having() option (or the having() option is not set), syslog-ng OSE generates and sends the message set in the aggregate() option.

Declaration:

parser parser_name {
    grouping-by(
        key()
        having()
        aggregate()
        timeout()
    );
};