Like any major online service, Siri is constantly being updated behind the scenes to improve stability, scalability, and performance. This presentation is specific called out Apache Mesos as helping with all of that, as well as efficiency and latency, and the ability to more easily build out additional services. The Mesosphere blog:

Apple uses J.A.R.V.I.S. as its internal platform-as-a-service (similar in functionality to our open source Marathon framework) meaning it's an easier way for Siri's developers and engineers to deploy the services that the application needs to answer all those iOS users' voice queries. (If it answers them badly, blame the algorithms not the infrastructure.)

Yes, Apple engineers use geeky comic book codenames like Jarvis — the intelligent assistant in the Iron Man movies — for Siri. (They also use Stark, Iron Man's alter ego, for CarPlay. Wouldn't you?)

The take away here isn't Mesos or any particular component. The take away is that, just like with chipsets and software, Apple isn't slowing down when it comes to moving services technology forward, and that's good for everyone who uses it.

For more information on the ongoing evolution of Siri, check the link above.