ELK Stack

https://github.com/logstash-plugins/logstash-patterns-core/blob/master/patterns/grok-patterns

https://www.elastic.co/guide/en/logstash/current/plugins-filters-grok.html

https://www.digitalocean.com/community/tutorials/how-to-install-elasticsearch-logstash-and-kibana-elk-stack-on-ubuntu-14-04#set-up-filebeat-(add-client-servers)

https://www.digitalocean.com/community/tutorials/how-to-install-elasticsearch-logstash-and-kibana-elk-stack-on-ubuntu-14-04

https://www.digitalocean.com/community/tutorials/adding-logstash-filters-to-improve-centralized-logging

https://www.digitalocean.com/community/tutorials/how-to-map-user-location-with-geoip-and-elk-elasticsearch-logstash-and-kibana

https://github.com/kkos/oniguruma/blob/master/doc/RE