Enriching log messages with external data
To properly interpret the events that the log messages describe, you must be able to handle log messages as part of a system of events, instead of individual information chunks. The syslog-ng PE application allows you to import data from external sources to include in the log messages, thus extending, enriching, and complementing the data found in the log message.
The syslog-ng PE application currently provides the following possibilities to enrich log messages.
In syslog-ng PE version 7.0 and later, you can use an external database file to add additional metadata to your log messages. For example, you can create a database (or export it from an existing tool) that contains a list of hostnames or IP addresses, and the department of your organization that the host belongs to, the role of the host (mailserver, webserver, and so on), or similar contextual information.
The database file is a simple text file in comma-separated value (CSV) format, where each line contains the following information:
-
A selector or ID that appears in the log messages, or the name of a filter that matches the messages, for example, the hostname.
-
The name of the name-value pair that syslog-ng PE adds to matching log messages.
-
The value of the name-value pairs.
For example, the following csv-file contains three lines identified with the IP address, and adds the host-role field to the log message.
192.168.1.1,host-role,webserver
192.168.2.1,host-role,firewall
192.168.3.1,host-role,mailserver
The database file
The database file must comply with the RFC4180 CSV format, with the following exceptions and limitations:
To add multiple name-value pairs to a message, include a separate line in the database for each name-value pair, for example:
192.168.1.1,host-role,webserver
192.168.1.1,contact-person,"John Doe"
192.168.1.1,contact-email,johndoe@example.com
Technically, add-contextual-data() is a parser in syslog-ng PE so you have to define it as a parser object.
Declaration
parser p_add_context_data {
add-contextual-data(
selector("$HOST"),
database("context-info-db.csv"),
);
};
You can also add data to messages that do not have a matching selector entry in the database using the default-selector() option.
If you modify the database file, you have to reload syslog-ng PE for the changes to take effect. If reloading syslog-ng PE or the database file fails for some reason, syslog-ng PE will keep using the last working database file.
Example: Adding metadata from a CSV file
The following example defines uses a CSV database to add the role of the host based on its IP address, and prefixes the added name-value pairs with .metadata. The destination includes a template that simply appends the added name-value pairs to the end of the log message.
@include "scl.conf"
source s_network {
network(port(5555));
};
destination d_local {
file("/tmp/test-msgs.log"
template("$MSG Additional metadata:[${.metadata.host-role}]")};
parser p_add_context_data {
add-contextual-data(
selector("$SOURCEIP"),
database("context-info-db.csv"),
default-selector("unknown"),
prefix(".metadata.")
);
};
log {
source(s_network);
parser(p_add_context_data);
destination(d_local);
};192.168.1.1,host-role,webserver
192.168.2.1,host-role,firewall
192.168.3.1,host-role,mailserver
unknown,host-role,unknown
To better control to which log messages you add contextual data, you can use filters as selectors. In this case, the first column of the CSV database file must contain the name of a filter. For each message, syslog-ng PE evaluates the filters in the order they appear in the database file. If a filter matches the message, syslog-ng PE adds the name-value pair related to the filter.
For example, the database file can contain the entries. (For details on the accepted CSV-format, see database().)
f_auth,domain,all
f_localhost,source,localhost
f_kern,domain,kernel
Note that syslog-ng PE does not evaluate other filters after the first match. For example, if you use the previous database file, and a message matches both the f_auth and f_localhost filters, syslog-ng PE adds only the name-value pair of f_auth to the message.
To add multiple name-value pairs to a message, include a separate line in the database for each name-value pair, for example:
f_localhost,host-role,firewall
f_localhost,contact-person,"John Doe"
f_localhost,contact-email,johndoe@example.com
You can also add data to messages that do not have a matching selector entry in the database using the default-selector() option.
You must store the filters you reference in a database in a separate file. This file is similar to a syslog-ng PE configuration file, but must contain only a version string and filters (and optionally comments). You can use the syslog-ng --syntax-only <filename> command to ensure that the file is valid. For example, the content of such a file can be:
@version: 7.0
filter f_localhost { host("mymachine.example.com") };
filter f_auth { facility(4) };
filter f_kern { facility(0) };
Declaration
parser p_add_context_data_filter {
add-contextual-data(
selector(filters("filters.conf")),
database("context-info-db.csv"),
prefix(".metadata.")
);
};
If you modify the database file, or the file that contains the filters, you have to reload syslog-ng PE for the changes to take effect. If reloading syslog-ng PE or the files fails for some reason, syslog-ng PE will keep using the last working version of the file.
The add-contextual-data() has the following options.
Required options
The following options are required: selector(), database().
database()
| Type: |
<path-to-file>.csv |
| Default: |
|
Description: Specifies the path to the CSV file, for example, /opt/syslog-ng/my-csv-database.csv. The extension of the file must be .csv, and can include Windows-style (CRLF) or UNIX-style (LF) linebreaks. You can use absolute path, or relative to the syslog-ng PE binary.
default-selector()
| Synopsis: |
default-selector() |
Description: Specifies the ID of the entry (line) that is corresponds to log messages that do not have a selector that matches an entry in the database. For example, if you add name-value pairs from the database based on the hostname from the log message (selector("${HOST}")), then you can include a line for unknown hosts in the database, and set default-selector() to the ID of the line for unknown hosts. In the CSV file:
unknown-hostname,host-role,unknown
In the syslog-ng PE configuration file:
add-contextual-data(
selector("$HOST")
database("context-info-db.csv")
default-selector("unknown-hostname")
);
prefix()
Description: Insert a prefix before the name part of the added name-value pairs (including the pairs added by the default-selector()) to help further processing.
selector()
Description: Specifies the string or macro that syslog-ng PE evaluates for each message, and if its value matches the ID of an entry in the database, syslog-ng PE adds the name-value pair of every matching database entry to the log message. Currently, you can use strings and a single macro (for example, ${HOST}) in the selector() option, templates are not supported. To use filters as selectors, see Using filters as selector.
