Always finance, trading systems. In the last 15 years mostly what they call "front office".

At the moment, for the place I work, we deploy on AWS mostly (because that is where our target trading venues often are). DB backends are largely not something we think about too much, because all of that is done out of band of course as a final state. Our main persistence is through our "bus" using aeron, and everything starts and recovers from there. This is not your typical enterprise java. No Spring.