Grok is a tool to parse crappy unstructured log data into something structured
and queryable. Grok is heavily used in Logstash to provide log data as input for
ElasticSearch.

Grok ships with about 120 predefined patterns for syslog logs, apache and other
webserver logs, mysql logs, etc. It is easy to extend Grok with custom patterns.

The grok_exporter aims at porting Grok from the ELK stack to Prometheus
monitoring. The goal is to use Grok patterns for extracting Prometheus metrics
from arbitrary log files.