Message representation in syslog-ng OSE
When the syslog-ng OSE application receives a message, it automatically parses the message. The syslog-ng OSE application can automatically parse log messages that conform to the RFC3164 (BSD or legacy-syslog) or the RFC5424 (IETF-syslog) message formats. If syslog-ng OSE cannot parse a message, it results in an error.
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TIP:
In case you need to relay messages that cannot be parsed without any modifications or changes, use the flags(no-parse) option in the source definition, and a template containing only the ${MESSAGE} macro in the destination definition. To parse non-syslog messages, for example, JSON, CSV, or other messages, you can use the built-in parsers of syslog-ng OSE. For details, see parser: Parse and segment structured messages. |
A parsed syslog message has the following parts.
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Timestamps
Two timestamps are associated with every message: one is the timestamp contained within the message (that is, when the sender sent the message), the other is the time when syslog-ng OSE has actually received the message.
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Severity
The severity of the message.
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Facility
The facility that sent the message.
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Tags
Custom text labels added to the message that are mainly used for filtering. None of the current message transport protocols adds tags to the log messages. Tags can be added to the log message only within syslog-ng OSE. The syslog-ng OSE application automatically adds the id of the source as a tag to the incoming messages. Other tags can be added to the message by the pattern database, or using the tags() option of the source.
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IP address of the sender
The IP address of the host that sent the message. Note that the IP address of the sender is a hard macro and cannot be modified within syslog-ng OSE but the associated hostname can be modified, for example, using rewrite rules.
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Hard macros
Hard macros contain data that is directly derived from the log message, for example, the ${MONTH} macro derives its value from the timestamp. The most important consideration with hard macros is that they are read-only, meaning they cannot be modified using rewrite rules or other means.
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Soft macros
Soft macros (sometimes also called name-value pairs) are either built-in macros automatically generated from the log message (for example, ${HOST}), or custom user-created macros generated by using the syslog-ng pattern database or a CSV-parser. The SDATA fields of RFC5424-formatted log messages become soft macros as well. In contrast with hard macros, soft macros are writable and can be modified within syslog-ng OSE, for example, using rewrite rules.
NOTE: It is also possible to set the value of built-in soft macros using parsers, for example, to set the ${HOST} macro from the message using a column of a CSV-parser.
The data extracted from the log messages using named pattern parsers in the pattern database are also soft macros.
TIP: For the list of hard and soft macros, see Hard vs. soft macros.
Message size and encoding
Internally, syslog-ng OSE represents every message as UTF-8. The maximal length of the log messages is limited by the log-msg-size() option: if a message is longer than this value, syslog-ng OSE truncates the message at the location it reaches the log-msg-size() value, and discards the rest of the message.
When encoding is set in a source (using the encoding() option) and the message is longer (in bytes) than log-msg-size() in UTF-8 representation, syslog-ng OSE splits the message at an undefined location (because the conversion between different encodings is not trivial).
Structuring macros, metadata, and other value-pairs
Available in syslog-ng OSE
The syslog-ng OSE application allows you to select and construct name-value pairs from any information already available about the log message, or extracted from the message itself. You can directly use this structured information, for example, in the following places:
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amqp() destination
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format-welf() template function
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mongodb() destination
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stomp() destination
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or in other destinations using the format-json() template function.
When using value-pairs, there are three ways to specify which information (that is, macros or other name-value pairs) to include in the selection.
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Select groups of macros using the scope() parameter, and optionally remove certain macros from the group using the exclude() parameter.
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List specific macros to include using the key() parameter.
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Define new name-value pairs to include using the pair() parameter.
These parameters are detailed in value-pairs().
Specifying data types in value-pairs
By default, syslog-ng OSE handles every data as strings. However, certain destinations and data formats (for example, SQL, MongoDB, JSON
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Caution:
Hazard of data loss! If syslog-ng OSE cannot convert the data into the specified type, an error occurs, and syslog-ng OSE drops the message by default. To change how syslog-ng OSE handles data-conversion errors, see on-error(). |
To use type-hinting, enclose the macro or template containing the data with the type: <datatype>("<macro>"), for example: int("$PID").
Currently the mongodb() destination and the format-json template function supports data types.
Example: Using type-hinting
The following example stores the MESSAGE, PID, DATE, and PROGRAM fields of a log message in a MongoDB database. The DATE and PID parts are stored as numbers instead of strings.
mongodb(
value-pairs(pair("date", datetime("$UNIXTIME"))
pair("pid", int64("$PID"))
pair("program", "$PROGRAM"))
pair("message", "$MESSAGE"))
)
);
The following example formats the same fields into JSON.
$(format-json date=datetime($UNIXTIME) pid=int64($PID) program=$PROGRAM message=$MESSAGE)
The syslog-ng OSE application currently supports the following data-types.
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boolean: Converts the data to a boolean value. Anything that begins with a t or 1 is converted to true, anything that begins with an f or 0 is converted to false.
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datetime: Use it only with UNIX timestamps, anything else will likely result in an error. This means that currently you can use only the $UNIXTIME macro for this purpose.
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double: A floating-point number.
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literal: The data as a literal string, without adding any quotes or escape characters.
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int or int32: 32-bit integer.
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int64: 64-bit integer.
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string: The data as a string.
value-pairs()
| Type: | parameter list of the value-pairs() option |
| Default: | empty string |
Description: The value-pairs() option allows you to select specific information about a message easily using predefined macro groups. The selected information is represented as name-value pairs and can be used formatted to JSON format, or directly used in a mongodb() destination.
Example: Using the value-pairs() option
The following example selects every available information about the log message, except for the date-related macros (R_* and S_*), selects the .SDATA.meta.sequenceId macro, and defines a new value-pair called MSGHDR that contains the program name and PID of the application that sent the log message.
value-pairs(
scope(nv_pairs core syslog all_macros selected_macros everything)
exclude("R_*")
exclude("S_*")
key(".SDATA.meta.sequenceId")
pair("MSGHDR" "$PROGRAM[$PID]: ")
)
The following example selects the same information as the previous example, but converts it into JSON format.
$(format-json --scope nv_pairs,core,syslog,all_macros,selected_macros,everything \
--exclude R_* --exclude S_* --key .SDATA.meta.sequenceId \
--pair MSGHDR="$PROGRAM[$PID]: ")|
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NOTE:
Every macro is included in the selection only once, but redundant information may appear if multiple macros include the same information (for example, including several date-related macros in the selection). |
The value-pairs() option has the following parameters. The parameters are evaluated in the following order:
| rekey() | |
| Type: | <pattern-to-select-names>, <list of transformations> |
| Default: | empty string |
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Description: This option allows you to manipulate and modify the name of the value-pairs. You can define transformations, which are are applied to the selected name-value pairs. The first parameter of the rekey() option is a glob pattern that selects the name-value pairs to modify. If you omit the pattern, the transformations are applied to every key of the scope. For details on globs, see glob. If you want to modify the names of several message fields, see also map-value-pairs: Rename value-pairs to normalize logs.
The following transformations are available:
Example: Using the rekey() optionThe following sample selects every value-pair that begins with .cee., deletes this prefix by cutting 4 characters from the names, and adds a new prefix (events.). value-pairs(
key(".cee.*"
rekey(
shift(4)
add-prefix("events.")
)
)
)
The rekey() option can be used with the format-json template-function as well, using the following syntax: $(format-json --rekey .cee.* --add-prefix events.) | |