Build geo searching ::

Build search index based on hash coordinate. Load danish addresses with coordinate into solr. MariaDB also support this but NOT with 4.7 millions records.

How many rows !

Build php import framework to import and update all danish address. 4.7 millions records.

... Build raspberry pi monitor ::

contain one raspbarry pi with 7" screen. Use nmap to lightly scan network segments every 60 sec with cron and throw it in db. Build webpage that look in db. simple and no rocket science when using linux, php and jQuery.

... Build raspberry pi rack ::

contain webserver, databaseserver, redisserver, queueserver and indexserver. Connectet wired with a small switch. Webserver act as router with wifi connection. Use it as dev server today. Connect to webserver with nfs from my windows. Perfect and mobile setup.