You're right, the ship n°121 is a Petya-class corvette, which was abandonned by Russia after the USSR collapse because she was unservicable. She was refitted by Azerbaidjan and returned to sea two or three years ago. the RBU isn't really important but Iran has at least one submersible in the Caspian Sea (the only Nahang-class sub).
Israel has signed with Azerbaijan, another big military contract
Israeli concern "Aviation industry" has signed a contract with Azerbaijan for the supply of a few tens of unmanned aerial vehicles.
"Negotiations between the parties lasted long enough and successful.
This is a significant contract in excess of such an agreement with Turkey, which was estimated by experts at $ 300 million ", - said the Israeli media.
Earlier, Azerbaijan has reached an agreement with Israel to purchase arms for a total of $ 1.6 billion