Armstrong's contract was selected by the Rays on Tuesday.
Armstrong was acquired in exchange for cash considerations from the Orioles at the deadline. He's been mediocre at best for most of his seven-year big-league career, posting a 4.65 ERA over 151 innings of work. Mike Brosseau was optioned to clear a space on the active roster, while Kevin Padlo was designated for assignment to make room on the 40-man.