Grok is a powerful plugin in Logstash that allows you to parse unstructured log data into structured data. Grok patterns are essentially regular expressions with predefined names for commonly used patterns, making it easier to write and maintain complex patterns.
Here are some examples of Grok patterns and their uses in Logstash:
Common Apache access log format:
%{COMBINEDAPACHELOG}
This pattern matches the common Apache access log format, including the IP address, timestamp, request method, URI, HTTP version, response status code, and more.
Syslog messages:
%{SYSLOGTIMESTAMP:timestamp} %{SYSLOGHOST:host} %{DATA:program}[%{POSINT:pid}]: %{GREEDYDATA:message}
This pattern matches syslog messages, including the timestamp, hostname, program name, process ID, and message.
Cisco ASA firewall logs:
%{CISCOTIMESTAMP:timestamp} %{IP:src_ip} %{CISCO_REASON:reason} %{GREEDYDATA:log_message}
This pattern matches Cisco ASA firewall logs, including the timestamp, source IP address, reason for the log, and log message.
Windows Event Log:
%{TIMESTAMP_ISO8601:timestamp} %{NUMBER:event_id:int} %{WORD:event_level} %{WORD:source} %{GREEDYDATA:message}
This pattern matches Windows Event Log messages, including the timestamp, event ID, event level, source, and message.
JSON logs:
%{TIMESTAMP_ISO8601:timestamp} %{DATA:logger} %{DATA:loglevel} \[%{DATA:thread}\] %{DATA:class} - %{GREEDYDATA:message}
This pattern matches JSON logs, including the timestamp, logger name, log level, thread name, class name, and message.
These are just a few examples of Grok patterns that can be used in Logstash to parse and structure log data. You can also create custom patterns for your specific needs. The Grok plugin is a powerful tool for making sense of unstructured log data, and can greatly simplify the process of log analysis and monitoring.
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