Standalone Solr Listen to Localhost only

I like firewalls as much a the next man. But sometimes they're just not necessary. Back in the day (back in the world of banking) I used to review sites that had a liberal sprinkling of firewalls. Literally. I remember one site that had as many firewalls as they did servers!

One of the key issues that changed this situation was explaining to people about ports. If something isnt listening on that port, then you dont need a firewall. Simples. Well, in practice you need to stop and detect unauthorised ingress and egress, tcp connection and protocol checking etc but for the vast majority of sites this can and should be performed at a choke point. Not on every piece of infrastructure for the sake of it. Least of all because it will chew up your staffs time monitoring, patching, key cycling etc.

Much better, where possible, to have a belt and braces approach and not listen on the network unless you really want to. Some software like solr comes with a pretty open default (you're meant to be a professional...) so to make solr listen on localhost only you have to add this into the jetty config in etc/jetty.xml