Iran is a vassal of Russia. Iran, like Russia, “views Turkey’s regional ambitions and the possible spread of some form of pan-Turkic ideology with suspicion.So they are drawn together in one aspect.Russia still has plans to finish the nuclear project at Bushehr.
I would argue that Iran is not the vassel of Russia. Iran is the customer of Russia. They do have common interests but not that of a fuedal serf to his lord.
Russia is dying and pretty much unable to muster the military where with all to be a threat.