logstash: add page (#1245)

pages/common/logstash.md

@@ -0,0 +1,15 @@
+# logstash
+
+> An ETL(extract, transform and load) tool, usually used to ingest data from various sources, like databases and flat log files into elasticsearch.
+
+- Check validity of a logstash configuration:
+
+`logstash --configtest --config {{logstash_config.conf}}`
+
+- Run logstash using configuration:
+
+`sudo logstash --config {{logstash_config.conf}}`
+
+- Run logstash with the most basic inline configuration string:
+
+`sudo logstash -e 'input {} filter {} output {}'`