An introduction to machine-learned ranking in Apache Solr

This tutorial describes how to implement a modern learning to rank (LTR, also called machine-learned ranking) system in Apache Solr. It's intended for people who have zero Solr experience, but who are comfortable with machine learning and information retrieval concepts. I was one of those people only a couple of months ago, and I found it extremely challenging to get up and running with the Solr materials I found online. This is my attempt at writing the tutorial I wish I had when I was getting started. Firing up a vanilla Solr instance on Linux (Fedora, in my case) is actually pretty straightforward.