I'm Afraid You've Got Dragons - Peter S Beagle

Dragons are common in the backwater kingdom of Bellemontagne, coming in sizes from mouse-like vermin all the way up to castle-smashing monsters. Gaius Aurelius Constantine Heliogabalus Thrax (who would much rather people call him Robert) has recently inherited his deceased dad's dead job as a dragon catcher/exterminator, a career he detests with all his heart in part because he likes dragons, feeling a kinship with them, but mainly because his dream has always been the impossible one of transcending his humble origin to someday become a prince's valet. Needless to say, fate has something rather different in mind...