Working in financial front-office since several years from now, I'm used to build reactive systems.
In a nutshell, they are systems that are ready to respond to stimuli (whether market data updates, client requests for prices, spreads modifications, position changes, etc), in order to react as quick as possible (in milliseconds or less), in a world where you must constantly protect you against waves or throughput peaks of data coming into your systems.
To achieve that, we mostly build systems that are event-driven, stream-oriented, scalable (vertically, but also horizontally), performant (with conflation enabled, GC-less strategies, ...), and resilient (i.e. recovery-oriented & production ready).
Today, one of my mate showed me this new reactive manifesto which is all about that kind of systems we used to build. I found it very readable and informative. Check this out by yourself:
And welcome to our reactive world!