...and then there are foreign fighters who by virtue of fighting on the Russian side in occupied East Ukraine are by definition agents of the Russian Federation with some degree of relationship to Russian intelligence services (at minimum GRU). No one just shows up in Rostov and gets incorporated into a military unit in Donbass. They have to know people, which makes their social networks interesting.
The graph below is based on publicly viewable relationships and interactions on Facebook. The seeds included four men who by their own admission have fought on the Russian side: Alexis Castillo of Colombia via Spain; Giuliano Elia of Italy; and Zak Novak & Russell Bentley representing the USA. Their friends are grouped based on shared relationships. Who among these friends inspired these gentlemen to join the fray, and who served to facilitate their doing so? These are questions for others to answer.