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Put simply, grok is a way to match a line against a regular expression, map specific parts of the line into dedicated fields, and perform actions based on this mapping. Built-in, there are over 200 Logstash patterns for filtering items such as words, numbers, and dates in AWS, Bacula, Bro, Linux-Syslog and more. If you cannot find the pattern you need, you can write your own custom pattern. There are also options for multiple match patterns, which simplifies the writing of expressions to capture log data. Here is the basic syntax format for a Logstash grok filter: %{SYNTAX:SEMANTIC} The SYNTAX will designate the pattern in the text of each log. The SEMANTIC will be the identifying mark that you actually give that syntax in your parsed logs. In other words: %{PATTERN:FieldName} This will match the predefined pattern and map it to a specific identifying field. For example, a pattern like 127.0.0.1 will match the Grok IP pattern, usually an IPv4 pattern. Grok has separate IPv4 and IPv6 patterns, but they can be filtered together with the syntax IP. This standard pattern is as follows: IPV4 (?<![0-9])(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))(?![0-9]) Pretending there was no unifying IP syntax, you would simply grok both with the same semantic field name: %{IPv4:Client IP} %{IPv6:Client IP} Again, just use the IP syntax, unless for any reason you want to separate these respective addresses into separate fields. Since grok is essentially based upon a combination of regular expressions, you can also create your own custom regex-based grok filter with this pattern: (?<custom_field>custom pattern) For example: (?\d\d-\d\d-\d\d) This grok pattern will match the regex of 22-22-22 (or any other digit) to the field name.
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Jan 31, 2021 16:31
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| # ¿ May 16, 2024 02:21 |
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