Routing your logs with syslog-ng
Note: This page describes routing logs with syslog-ng. If you are using Fluentd to route your log messages, see Routing your logs with Fluentd match directives.
syslog-ng is supported only in Logging operator 4.0 or newer.
The first step to process your logs is to select which logs go where.
The match
field of the SyslogNGFlow
and SyslogNGClusterFlow
resources define the routing rules of the logs.
Note: Fluentd can use only metadata to route the logs. When using syslog-ng filter expressions, you can filter both on metadata and log content as well.
The syntax of syslog-ng match statements is slightly different from the Fluentd match statements.
Available routing metadata keys:
Name | Type | Description | Empty |
---|---|---|---|
namespaces | []string | List of matching namespaces | All namespaces |
labels | map[string]string | Key - Value pairs of labels | All labels |
hosts | []string | List of matching hosts | All hosts |
container_names | []string | List of matching containers (not Pods) | All containers |
Match statement
Match expressions select messages by applying patterns on the content or metadata of the messages. You can use simple string matching, and also complex regular expressions. You can combine matches using the and
, or
, and not
boolean operators to create complex expressions to select or exclude messages as needed for your use case.
Currently, only a pattern matching function is supported (called match
in syslog-ng parlance, but renamed to regexp
in the CRD to avoid confusion).
The match
field can have one of the following options:
-
regexp
: A pattern that matches the value of a field or a templated value. For example: -
and
: Combines the nested match expressions with the logical AND operator. -
or
: Combines the nested match expressions with the logical OR operator. -
not
: Matches the logical NOT of the nested match expressions with the logical AND operator.
regexp
patterns
The regexp
field (called match
in syslog-ng parlance, but renamed to regexp
in the CRD to avoid confusion) defines the pattern that selects the matching messages. You can do two different kinds of matching:
- Find a pattern in the value of a field of the messages, for example, to select the messages of a specific application. To do that, set the
pattern
andvalue
fields (and optionally thetype
andflags
fields). - Find a pattern in a template expression created from multiple fields of the message. To do that, set the
pattern
andtemplate
fields (and optionally thetype
andflags
fields).
CAUTION:
You need to use thejson.
prefix in field names.
You can reference fields using the dot notation. For example, if the log contains {"kubernetes": {"namespace_name": "default"}}
, then you can reference the namespace_name
field using json.kubernetes.namespace_name
.
The following example filters for specific Pod labels:
regexp
parameters
The regexp
field can have the following parameters:
pattern
(string)
Defines the pattern to match against the messages. The type
field determines how the pattern is interpreted (for example, string or regular expression).
value
(string)
References a field of the message. The pattern
is applied to the value of this field. If the value
field is set, you cannot use the template
field.
CAUTION:
You need to use thejson.
prefix in field names.
You can reference fields using the dot notation. For example, if the log contains {"kubernetes": {"namespace_name": "default"}}
, then you can reference the namespace_name
field using json.kubernetes.namespace_name
.
For example:
template
(string)
Specifies a template expression that combines fields. The pattern
is matched against the value of these combined fields. If the template
field is set, you cannot use the value
field. For details on template expressions, see the syslog-ng documentation.
type
(string)
Specifies how the pattern
is interpreted. For details, see Types of regexp
.
flags
(list)
Specifies flags for the type
field.
regexp
types
By default, syslog-ng uses PCRE-style regular expressions. Since evaluating complex regular expressions can greatly increase CPU usage and are not always needed, you can following expression types:
- Perl Compatible Regular Expressions (PCRE)
- Literal string searches
- Glob patterns (without regular expression support)
pcre
Description: Use Perl Compatible Regular Expressions (PCRE). If the type()
parameter is not specified, syslog-ng uses PCRE regular expressions by default.
pcre
flags
PCRE regular expressions have the following flag options:
-
disable-jit
: Disable the just-in-time compilation function for PCRE regular expressions. -
dupnames
: Allow using duplicate names for named subpatterns. -
global
: Usable only in rewrite rules: match for every occurrence of the expression, not only the first one. -
ignore-case
: Disable case-sensitivity. -
newline
: When configured, it changes the newline definition used in PCRE regular expressions to accept either of the following:- a single carriage-return
- linefeed
- the sequence carriage-return and linefeed (\r, \n and \r\n, respectively)
This newline definition is used when the circumflex and dollar patterns (^ and $) are matched against an input. By default, PCRE interprets the linefeed character as indicating the end of a line. It does not affect the \r, \n or \R characters used in patterns.
-
store-matches
: Store the matches of the regular expression into the $0, … $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example (?<name>...
), are stored as well. Matches from the last filter expression can be referenced in regular expressions. -
unicode
: Use Unicode support for UTF-8 matches. UTF-8 character sequences are handled as single characters. -
utf8
: An alias for the unicode flag.
For example:
For details, see the documentation of the AxoSyslog syslog-ng distribution.
string
Description: Match the strings literally, without regular expression support. By default, only identical strings are matched. For partial matches, use the flags: prefix
or flags: substring
flags. For example, if the consider the following patterns.
- The first matches only the
log-generator
label. - The second matches labels beginning with
log-generator
, for example,log-generator-1
. - The third one matches labels that contain the
log-generator
string, for example,my-log-generator
.
string
flags
Literal string searches have the following flags()
options:
-
global
: Usable only in rewrite rules, match for every occurrence of the expression, not only the first one. -
ignore-case
: Disables case-sensitivity. -
prefix
: During the matching process, patterns (also called search expressions) are matched against the input string starting from the beginning of the input string, and the input string is matched only for the maximum character length of the pattern. The initial characters of the pattern and the input string must be identical in the exact same order, and the pattern’s length is definitive for the matching process (that is, if the pattern is longer than the input string, the match will fail).For example, for the input string
exam
:- the following patterns will match:
ex
(the pattern contains the initial characters of the input string in the exact same order)exam
(the pattern is an exact match for the input string)
- the following patterns will not match:
example
(the pattern is longer than the input string)hexameter
(the pattern’s initial characters do not match the input string’s characters in the exact same order, and the pattern is longer than the input string)
- the following patterns will match:
-
store-matches
: Stores the matches of the regular expression into the $0, … $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example, (?<name>...
), are stored as well. Matches from the last filter expression can be referenced in regular expressions.NOTE: To convert match variables into a syslog-ng list, use the
$*
macro, which can be further manipulated using List manipulation, or turned into a list in type-aware destinations. -
substring
: The given literal string will match when the pattern is found within the input. Unlikeflags: prefix
, the pattern does not have to be identical with the given literal string.
For details, see the documentation of the AxoSyslog syslog-ng distribution.
glob
Description: Match the strings against a pattern containing ‘*’ and ‘?’ wildcards, without regular expression and character range support. The advantage of glob patterns to regular expressions is that globs can be processed much faster.
*
: matches an arbitrary string, including an empty string?
: matches an arbitrary character
NOTE:
- The wildcards can match the
/
character.- You cannot use the
*
and?
characters literally in the pattern.
Glob patterns cannot have any flags.
Examples
Select all logs
To select all logs, or if you only want to exclude some logs but retain others you need an empty select statement.
Select logs by label
Select logs with app: nginx
labels from the namespace:
Exclude logs by label
Exclude logs with app: nginx
labels from the namespace.
Exclude and select logs by label
Exclude logs with env: dev
labels but select app: nginx
labels from the namespace.
Multiple labels - AND
Exclude logs that have both the app: nginx
and app.kubernetes.io/instance: nginx-demo
labels.
Multiple labels - OR
Exclude logs that have either the app: nginx
or the app.kubernetes.io/instance: nginx-demo
labels