Agathias, Histories 1.19. Bonus was in fact quaestor (cf. kappa 2533) of Moesia, according to Agathias, but had been entrusted with a sizeable military force by the Byzantine general Narses (cf. nu 42) for securing the environs of Luca (modern-day Lucca, in Tuscany, Italy; cf. alpha 457) in 553 CE; cf. Frendo (27) and PLRE IIIa s.v. Bonus(1).
It is possible that there is some confusion on the part of the Suda lexicographer here. A later Bonus was indeed a general in 568-569/570, commanding Roman forces defending the city of Sirmium from Avar assaults; cf. PLRE IIIa s.v. Bonus(4), alpha 3252, epsilon 3875, and sigma 1653. In 561 he was tasked by Justin (the Roman general in Lazika and Thrace, not the future emperor; cf. PLRE IIIa s.v. Iustinus(4)) with guarding the Danube frontier against the Avars. On the Avars see alpha 18 generally.
[1] In other words, Moesia (to be distinguished from Mysia in Asia Minor: mu 1472, etc.), Barrington Atlas map 100 grids L3-M3. The two place-names are homophonous in Byzantine pronunciation; and see further under delta 23.